Passing the State Science Proficiency Tests : Essential Content for Elementary and Middle School Teachers 9780761862642, 9780761862635

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PASSING THE STATE SCIENCE PROFICIENCY TESTS

_________________________ Essential Content for Elementary and Middle School Teachers

_________________________ Edited by Craig A. Wilson

University Press of America,® Inc. Lanham · Boulder · New York · Toronto · Plymouth, UK

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Passing the State Science Proficiency Tests: Essential Content for Elementary and Middle School Teachers

edited by

Craig A. Wilson

East Stroudsburg University

Table of Contents (brief) Acknowledgements Introduction

xi xiii

Part I. Scientific Methodology, Techniques, and History 1. Methodology and Philosophy 2. Mathematics, Measurement, and Data Manipulation 3. Laboratory Procedures and Safety—Part I 4. Laboratory Procedures and Safety—Part II

2 10 24 31

Part II. Basic Principles 5. Matter and Energy 6. Heat and Thermodynamics 7. Atomic and Nuclear Structure

36 45 51

Part III. Physical Sciences (Physics) 8. Mechanics 9. Electricity and Magnetism 10. Wave Phenomenon

69 87 96

Part IV. Physical Sciences (Chemistry) 11. Periodicity 12. The Mole and Chemical Bonding 13. States of Matter 14. Chemical Reactions 15. Solutions and Solubility

121 130 142 148 161

Part V. Life Sciences 16. The Cell 17. DNA Structure 18. Diversity of Life 19. Plants 20. Animals—Part I 21. Animals—Part II 22. Ecology

169 179 191 203 214 223 241

Part VI. Earth Sciences 23. Physical Geology 24. Historical Geology 25. Oceanography 26. Meteorology 27. Astronomy

252 263 268 278 295

Table of Contents (brief)

iv

Part VII. Science, Technology, and Society 28. The Uses and Applications of Science and Technology in Daily Life 29. The Social, Political, Ethical and Economic Issues Arising from the Use of Certain Technologies About the Authors

314 323 331

Table of Contents (expanded) Acknowledgements Introduction How to Use this Book Part I. Scientific Methodology, Techniques, and History 1. Methodology and Philosophy Scientific Methods Scientific Facts, Models, Theories, and Laws Science Process Skills Historical Roots of Science

xi xiii

2

2. Mathematics, Measurement, and Data Manipulation Scientific Measurement and Notation Systems Scientific Data Collection, Manipulation, Interpretation, and Presentation Interpreting and Drawing Conclusions from Data Identifying Sources of Error in Data

10

3. Laboratory Procedures and Safety—Part I Safe Preparation, Storage, Use, and Disposal of Laboratory and Field Materials Appropriate Laboratory and Field Equipment Safety and Emergency Procedures

24

4. Laboratory Procedures and Safety—Part II Electrical First-Aid Fire Safety Sharp Instrument Safety

31

Part II. Basic Principles 5. Matter and Energy The Structure and Properties of Matter Factors That Influence the Occurrence of the Elements Physical and Chemical Changes of Matter Conservation of Mass and Energy Energy Transformations 6. Heat and Thermodynamics Temperature and Thermal Energy Effects of Thermal Energy on Matter

36

45

vi

Table of Contents (expanded)

Measurement and Transfer of Thermal Energy First and Second Laws of Thermodynamics 7. Atomic and Nuclear Structure Atomic Models and Their Experimental Bases Electron Arrangement and the Chemical Properties of Atoms Atomic and Nuclear Structure and Forces Electron Arrangement and the Physical Properties of Atoms Nuclear Reactions and Their Products Radioisotopes and Radioactivity Radioactive Dating Fusion Part III. Physical Sciences (Physics) 8. Mechanics Forms of Motion Newton’s Laws of Motion Friction Work, Energy, and Power Simple Machines and Torque Conservation of Energy and Momentum Gravitation Archimedes’ Principle Bernoulli’s Principle General Theory of Relativity 9. Electricity and Magnetism Repulsion and Attraction of Electric Charges Series and Parallel Circuits Conductors and Insulators Ohm’s Law Direct Current and Alternating Current Flow Sources of EMF Magnetic Fields and Magnetic Forces Transformers and Motors 10. Wave Phenomenon Transverse and Longitudinal Waves Wavelength, Amplitude, Frequency, Speed Reflection, Diffusion, Refraction, Absorption, Transmission Diffraction and Interference Doppler Effect Characteristics of Sound Waves Electromagnetic Spectrum

51

69

87

96

Table of Contents (expanded)

vii

Color and the Visible Spectrum Geometric Optics—Mirrors Geometric Optics—Lenses Part IV. Physical Sciences (Chemistry) 11. Periodicity Physical Periodicity Chemical Periodicity

121

12. The Mole and Chemical Bonding Mole Concept and Chemical Composition Chemical Formulas Types of Bonds Electron Dot and Structural Formulas Systematic Nomenclature of Inorganic Compounds Nomenclature of Simple Organic Compounds

130

13. States of Matter Properties of Solids, Liquids, and Gases Phase Changes Crystals The Ideal Gas Law and the Kinetic Molecular Theory

142

14. Chemical Reactions Balancing Chemical Equations Types of Chemical Equations Endothermic and Exothermic Chemical Reactions Effects of Temperature, Pressure, Concentration, and Catalysts on Chemical Reactions Practical Applications of Electrochemistry

148

Part V. Life Sciences 15. Solutions and Solubility Types of Solutions Solvents and Factors Affecting the Dissolving Process Effects of Temperature and Pressure on the Solubility of a Solute Physical and Chemical Properties of Acids and Bases pH and the Effects of Buffers 16. The Cell Prokaryotic and Eukaryotic Cells Structure and Function of Plasma Membranes and Organelles Chemical Reactions in Respiration and Photosynthesis The Cell Cycle: Interphase, Mitosis, Meiosis, and Cytokinesis

161

169

Table of Contents (expanded)

viii

17. DNA Structure DNA Replication Transcription Translation Causes and Results of Mutations Interaction Between Inheritance and Environment Mendelian Inheritance Non-Mendelian Inheritance Recombinant DNA

179

18. Diversity of Life Characteristics of Life and Biological Levels of Organization The Hierarchical Classification Scheme Characteristics of Viruses, Archaeabacteria, Eubacteria, Protists, Fungi, Plants, and Animals

191

19. Plants Nonvascular and Vascular Plants Structure and Function of Leaves, Stems, and Roots Control Mechanisms Photosynthesis and Respiration Water and Nutrient Uptake and Transport Systems Sexual and Asexual Reproduction

203

20. Animals—Part I Digestion Circulation Respiration Excretion Immunity

214

21. Animals—Part II Response to Stimuli Homeostasis Endocrine System Nervous Control Invertebrate Animals Vertebrate Animals The Musculoskeletal System The Muscular System

223

22. Ecology Population Dynamics Social Behaviors

241

Table of Contents (expanded)

ix

Intraspecific Competition Interspecific Relationships Succession Stability of Ecosystems and the Effects of Disturbances Energy Flow Biogeochemical Cycles Biomes Part VI. Earth Sciences 23. Physical Geology Mineral and Rock Formation Identification and Classification of Different Types of Minerals, Rocks and Soils Earth’s Layers Folding, Faulting, Earthquakes, and Volcanoes Plate Tectonic Theory Hydrologic Cycle Weathering, Erosion, and Deposition

252

24. Historical Geology Uniformitarianism Stratigraphy Relative and Absolute Time Fossil Record and Formation

263

25. Oceanography Geographic Location of the Oceans and Seas Formation and Movement of Ocean Waves Tides Surface and Deep-Water Currents Topography and Landforms of the Ocean Floor and Shorelines Physical and Chemical Properties of Seawater and Nutrient Cycles of the Ocean

268

26. Meteorology Atmospheric Layers Chemical Composition of the Atmosphere Seasonal, Latitudinal and Daily Variation of Solar Radiation Global Wind Belts Small-Scale Atmospheric Circulation Ways to Indicate the Moisture Content of the Air Cloud and Precipitation Types Major Types of Air Masses Low- and High-Pressure Systems

278

Table of Contents (expanded)

x

Frontal Systems Interpretation of Weather Maps Weather Forecasting Regional and Local Natural Factors that Affect Climate How Humans Affect and are Affected by Climate 27. Astronomy Units of Distance Origin and Life Cycle of Stars. Characteristics of the Sun The Solar System Earth’s Motion and Units of Time Earth’s Seasons Earth-Moon-Sun System Phases of the Moon Eclipses Satellites and Geosynchronous Orbits. Contributions of Manned and Unmanned Space Missions Scientific Contributions of Remote Sensing Part VII. Science, Technology, and Society 28. The Uses and Applications of Science and Technology in Daily Life Production and Transmission of Energy Production, Storage, Use, Management, and Disposal of Consumer Products Management of Natural Resources Nutrition and Public Health Issues Agricultural Practices 29. The Social, Political, Ethical and Economic Issues Arising from the Use of Certain Technologies Cloning, Prolonging Life, and Prenatal Testing The Impact of Science and Technology on the Environment and Human Affairs About the Authors

295

314

323

331

ACKNOWLEDGEMENTS Development of this book has involved a team effort and I want to express my strong appreciation to the many individuals who have made this possible. A sincere “thank you” goes to each of the following people: To the editors at the University Press of America, Julie Kirsch, Piper Owens, Laura Espinoza, Elaine Schleiffer, Lindsay Macdonald, Laura Grzybowski, and Stella Donovan for your patient guidance, timely suggestions, and positive encouragement throughout the process. To the authors of this book who spent many hours conducting research, organizing the content, submitting their manuscripts, and revising their work. This has truly been a collaborative effort that has brought science educators who shared a common goal together from all across the country. To my graduate assistants, Blaire Spooner and Nicole Wild, for your excellent help in communicating with the authors, proofreading the text, and offering valuable suggestions and to the graduate assistants at many other institutions who played an important role in helping the authors in the preparation of their chapters. To the leadership of The Association for Science Teacher Education who made it possible to communicate and collaborate with members of the association who were interested in becoming involved with this project. To my typesetter and illustrator, Andy Cross, for your professional expertise and careful attention to detail as you prepared this book for publication. You greatly enhanced the work on this project. To my loving wife and wonderful daughter, who were very patient with me as I spent many hours in the study working on this project. Thank you both for your understanding. Also, to my niece, Jessica Mosher, for all of your encouragement and interest in this endeavor.

INTRODUCTION Craig A. Wilson

It is imperative that elementary and middle school science teachers possess a strong grasp of the science content they are planning to teach. One reason this is so important is that research has shown there is a positive correlation between teachers’ science content background and their ability to teach science effectively. After conducting a review of over 200 studies, Darling Hammond & McLaughlin (1999) concluded that students whose teachers possess greater content background and knowledge of teaching are more successful in several fields, including math and science. Additionally, Wheeler (2006), the former Executive Director of the National Science Teachers Association, points out that teacher preparation programs need to do a better job of providing teachers with science content knowledge, because there is a positive correlation between teachers’ content knowledge and student achievement. Another reason it is important for elementary and middle school teachers to have a strong science content background is the “highly qualified” mandate of the No Child Left Behind (NCLB) Act. NCLB requires that all teachers in the United States be “highly qualified.” As a result, state departments of education have placed a greater emphasis on content background (as seen in Table I-1). Currently, 36 out of 50 states require elementary teachers to pass either a content test and/or a specialty area test that includes science content questions. Furthermore, 38 out of 50 states require that middle school science teachers pass a content test, and out of those 38 states, 26 require the PRAXIS II: Middle School Science Test.

xiv

Introduction

Table I-1 State Testing Requirements

Elementary Teaching Requirements PRAXIS II: Elementary Education Content Knowledge (0014) PRAXIS II: Elementary Education: Content Area Exercises (0012) PRAXIS II: Fundamental Subjects: Content Knowledge (0511) State Tests States with no content tests Middle School Teaching Requirements PRAXIS II: Middle School Science (0439) PRAXIS II: Middle School Content (0146) State Tests State with no content tests

Number of States 23 5 1 7 14 Number of States 26 3 9 12

This book is designed to help elementary and middle school preservice and inservice teachers review important science concepts in order to enhance their science content backgrounds. While there are many science textbooks that teachers could use to enhance their science content backgrounds, this book is unique in at least two ways. First, it combines all of this background information into one volume. Therefore, this book will save the reader many hours that would have otherwise been devoted to looking through multiple sources of information. Second, the authors of this book have attempted to avoid over-elaboration by including only essential content, due to the fact that research has indicated overelaboration can cause interference and thus have a detrimental effect on learning. While there is certainly much more that could have been written about each topic, the authors made every effort to control the amount of information that was presented, to keep with the main purpose of the book of providing a resource for reviewing important science content.

How to Use tHis Book Since 26 states currently utilize the PRAXIS Middle School Science Test, the topics addressed in this book are based on that test. There are 29 chapters in the book, divided into the following sections: Scientific Methodology, Techniques, and History; Basic Principles; Physical Sciences (Physics); Physical Sciences (Chemistry); Life Sciences; Earth Sciences; Science, Technology, and Society. If you live in a state that has its own test, this book would still be useful as a review, because the other state proficiency tests involve many of the same topics as those addressed on the PRAXIS Middle School Science Test.

Introduction

xv

The PRAXIS Middle School Science Test consists of 90 multiple choice questions and three constructed response questions. If you go to ets.org, you will find two important resources that you could use in conjunction with this book (click on The PRAXIS Series Test, click on Prepare for a Test, choose Middle School Science). The first document is entitled Test at a Glance and the second is an e-Book entitled Middle School Science Study Guide. Both of these resources provide an overview of the PRAXIS Middle School Science Test, along with some sample test questions and a detailed answer key. Following are suggested steps that you could use to prepare to take either the PRAXIS Middle School Science Test or your state’s science proficiency test for elementary or middle school science. 1. 2. 3.

4. 5. 6. 7. 8. 9.

Look over “Test at a Glance” for the PRAXIS Middle School Science Test (available free at ets.org). Purchase the Study Guide for the PRAXIS Middle School Science Test (available for $22.95 at ets.org). Look over Chapter 5 from the Study Guide, one topic at a time (i.e., “Methodology and Philosophy”). This chapter provides a complete outline of topics and subtopics, along with a few thought questions that have been interspersed along the way. Read the corresponding chapter for each topic from Passing the State Science Proficiency Tests: Essential Content for Elementary and Middle School Teachers. Answer the practice test questions at the end of each chapter of Passing the Science Proficiency Tests: Essential Content for Elementary and Middle School Teachers and check your answers with the answer key. Repeat steps 3-5 with each of the other 28 study topics. Answer the practice test questions from Chapter 6 of the Study Guide, and check your answers with the answer key. Look up and review topics in Passing the State Science Proficiency Tests: Essential Content for Elementary and Middle School Teachers that are still somewhat unclear. Take and pass your state’s science proficiency test! Works Cited

Darling-Hammond, L. & McLaughlin, M. W. “Investing in Teaching as a Learning Profession: Policy Problems and Prospects.” In L. Darling Hammond & G. Sykes (Eds.), Teaching as the Learning Profession: Handbook of Policy and Practice. San Francisco: Jossey Bass, 1999. Print. Wheeler, Gerald. “Strategies for Science Education Reform.” Education Leadership 64.4 (2006): 30-34. Print.

PART I SCIENTIFIC METHODOLOGY, TECHNIQUES, AND HISTORY

Chapter 1

METHODOLOGY AND PHILOSOPHY Craig A. Wilson

scientific MetHods Scientific methods are processes that are used to ask and answer questions about the physical world. They involve a series of steps, including the following: (a) pose a question, (b) develop a hypothesis, (c) carry out an experiment, and (d) draw a conclusion. The first step in the process is to pose a question. While posing a question, it is a good idea to conduct a background search because scientific research should build on what other scientists have discovered. In addition, it is instructive to consider strategies that have been used in the past to answer similar questions. The question that you pose should deal with a phenomenon that is measurable. For example, you might ask, “What factors affect the dissolving rate of a sugar cube?” Once you have posed a question, you should develop your hypotheses. A hypothesis is an educated guess, based on previous observations. Hypotheses are very specific due, to the fact that they relate to a single event. For the question posed above, one hypothesis might be, “Crushing a sugar cube will increase its dissolving rate,” and another might be, “Stirring the water will increase the dissolving rate of a sugar cube.” After you have developed your hypotheses, you will be ready to carry out an experiment, in order to test your hypotheses. Experimenting involves the three basic science processes of controlling variables, observing, and inferring. For example, in order to determine the effects of crushing on the dissolving rate of a sugar cube, you would control variables by putting three sugar cubes into three different beakers of water. Each beaker would contain the same amount of water

Methodology and Philosophy

3

at the same temperature. You would drop the first sugar cube into the beaker, crush the second sugar and then drop it into the water, and stir the third sugar cube, after it is dropped into the water. Next, you might use your sense of sight to observe that the crushed sugar cube dissolves fastest. You might further observe the specific amount of time that it takes for each of the sugar cubes to dissolve. Observing should be followed by inferring. In the sample experiment you might use what you observed about the sugar cube to explain that the crushed sugar cube dissolves faster because there is more surface area exposed to the water than the other sugar cube. The last step is to draw conclusions. This involves addressing each of your questions, based on the observations and inferences you made during the experiment. It is useful to relate your conclusions to the original hypotheses and to explain why you believe they either support or refute the expected results of the experiment. Finally, describe how your experiment could be refined in order to enhance the results.

scientific facts, Models, tHeories, and laws The terms facts, models, theories, and law are interrelated, but they all have very distinctive meanings. Scientific facts are things that can be directly observed with at least one or more of the five senses. For example, in an experiment with sugar cubes we could observe that several conditions affect the dissolving role of the sugar cubes. Models are used to represent what we know about a particular object or event. They are especially useful for depicting very small things that are too small to see clearly, or very large things that are difficult to access. Models are also valuable for illustrating complex topics. Models may not be completely accurate, however; for example, when scientists use drawings of magnetic domains to represent the poles of a magnet, the drawings are useful for explaining the reason for the magnetic poles, but they do not provide a complete picture of how the atoms would look if we could actually observe them. Scientific theories are complex explanations for a set of related phenomena, based on observations and inferences from many scientists. After multiple verifications a scientific theory is accepted by the broader scientific community. Scientific theories are dynamic, in that they are often modified as new information is obtained. Scientific laws are factual statements that are considered to be universally true. Laws govern a single type of action and are accepted by the entire scientific community because they have never been shown to be untrue. Laws are static rather than dynamic, because if a law did not match a particular phenomenon it would no longer apply.

4

Methodology and Philosophy

science Process skills Scientific inquiry involves answering scientific questions by using the scientific processes. Three of the most common science processes are controlling variables, observing, and inferring. As noted above, these processes are used when conducting an experiment. Controlling variables involves two important components. First, researchers should allow one factor to vary, and this is called the experimental variable. Second, they should keep the rest of the factors the same and they are called the constants. For example, when conducting a study on the effects of light on seed germination, three pots could be set up. Each pot would get a different amount of light (experimental variable), while each pot would get the same seeds, amount of soil, and water (constants). Observing involves using one or more of the five senses to gather data about objects and events. Whenever possible, it is important to make observations of the change. For example, “What happens to the iron filings when I bring a magnet close to them?” It is also important to use quantitative observation such as “Iron fillings within one inch of the magnet were attracted to the ends of the magnet.” An inference is a possible explanation of a scientific phenomenon based on observations. Therefore, it is important to distinguish between observations and inferences because inferences are much more subjective than observations. Many arguments could be avoided if we would use phrases such as “I think that…” rather than “I know that…” when discussing our inferences. It is also important to know when additional observations are needed. Scientists make several, careful observations, in order to avoid the pitfalls of logical thinking. For example, if you place a lighted candle in a shallow pan of water and then cover the candle with a small beaker, the candle will go out and water rise approximately one-fifth the height of the beaker. It might be inferred that this is because the candle used up the oxygen in the beaker and the water rose to take its place. However, further observations will indicate that the water rises in the beaker due to expansion and contraction, rather than because of the use of oxygen by the candle flame.

Historical roots of science The final report of Project 2061 from the American Association for the Advancement of Science (AAAS, 1990) provides information on ten significant scientific discoveries that occurred in Europe over the last 500 years. Six of those discoveries will be described briefly below, based on information found in the final report from AAAS.

Methodology and Philosophy

5

disPlacing tHe eartH froM tHe center of tHe Universe

For centuries it was believed that the earth was the center of the universe and that the stars orbited the earth in a perfect circle. An Egyptian astronomer named Ptolemy developed a mathematical model to explain and support the notion of an earth-centered universe, and that model was further refined by Arab and European astronomers (as shown in Figure 1.1)

Saturn

Sun

Earth Venus Moon

Mercury

Mars

Jupiter

Figure 1.1 Earth-Centered Universe (drawing by Andrew Cross)

It was not until the late 1400s that a Polish astronomer named Copernicus proposed a different model, one in which the earth and the other planets revolved around the sun. A German astronomer named Kepler further refined the Copernican model by postulating that the planets orbited the sun in ellipses rather than circles, and at varying speeds. Then an Italian scientist named Galileo, who lived at the same time as Kepler and Shakespeare, built a newly invented telescope. By using the telescope he was able to more closely observe the solar system and stars and this allowed him to make many discoveries that supported the Copernican model of planetary motion.

Uniting tHe Heavens and eartH

Near the end of the seventeenth century, an English scientist named Isaac Newton brought the work of Copernicus, Kepler, and Galileo together when he proposed a mathematical view of the world. Newton’s scientific ideas quickly spread to all of the sciences. In a monumental book, entitled Mathematical Principles of Natural Philosophy, Newton was able to explain the motion of planets, moons and comets, the motion of falling objects, and even the causes of ocean tides, based on a consistent set of mathematical principles.

6

Methodology and Philosophy

The effects of Newton’s work rippled through all of the sciences and even spread into philosophy. Some believed that one of the implications of Newtonian physics was that, since nature was governed by a predetermined sequence of events, there was no need to assume the existence of gods. In contrast, Newton believed that his philosophies demonstrated that there is a God who is in complete control of the universe.

relating sPace and tiMe and Matter and energy

It was not until the beginning of the twentieth century that some of Newton’s ideas were seriously questioned. A German born scientist named Albert Einstein published a paper on the special theory of relativity, which closely linked space and time, contrary to Newton who viewed them as different dimensions. The special theory of relativity also asserts that matter and energy are equivalent, since energy has mass and matter is a form of energy.

Moving tHe continents

Until early in the twentieth century it was commonly believed that the continents’ positions were fixed. At that time, a German scientist named Alfred Wegener presented evidence that indicated all of the continents were at one time linked as one gigantic continent that he called Pangea (as shown in Figure 1.2). Wegener observed that the underwater edges of continents fit together well, and that plants, animals, and fossils along the adjacent edges of the continents were very similar.

Eurasia

North America

Africa South America India Antarctica

Australia

Figure 1.2 Continent Position (drawing by Andrew Cross)

Methodology and Philosophy

7

As Wegener’s ideas were explored and additional evidence was gathered, the theory of plate tectonics developed. By the 1960s it was commonly accepted that the earth’s crust consisted of tectonic plates that are slowly moving over a bed of molten rock located under the plates. Today the theory of tectonics is used to explain such geological phenomena as earthquakes, volcanoes, and mountain formation.

sPlitting tHe atoM

At the beginning of the nineteenth century a polish scientist named Maria Curry observed that uranium was able to darken an unexposed photographic plate through its wrapping. Working with her husband, Pierre Curry, Maria was able to isolate traces of two radioactive elements—polonium and radium. Building on the work of the Curries a New Zealand born British scientist named Ernest Rutherford discovered that, as radioactive uranium decays, it emits particles that become light helium atoms. This discovery revealed the fact that the atoms are not the simplest unit of matter; rather, atoms consist of protons, neutrons, and electrons. Just before World War II, an Austrian physicist, Lisa Meitner, and her nephew, Otto Frisch, introduced the term “fission” to describe the process in which uranium is divided into new elements when it is irradiated by neutrons (as shown in Figure 1.3). During World War II an Italian born physicist, Enrico Fermi, led an American scientific team, as they developed the atomic bomb, which involves an uncontrolled fission reaction with uranium.

92

Kr

235

U

236

U

141

Ba

Figure 1.3 Splitting the Atom (drawing by Andrew Cross)

discovering gerMs

In the nineteenth century, a French chemist named Louis Pasteur discovered that microorganisms were responsible for spoilage in milk, fermentation in wine, and disease in animals. Pasteur also observed that when the body is infected by germs, it builds up immunities to fight future infections. This led to the discovery that vaccines could be developed to help the body build immunities to certain diseases.

8

Methodology and Philosophy

review QUestions—cHaPter 1 1. Which of the following basic science processes are involved with carrying out an experiment? a. Predicting, observing, inferring. b. Hypothesizing, observing, inferring. c. Predicting, observing, controlling variables. d. Controlling variables, observing, inferring. 2. Which of the following is true of scientific theories? a. They are dynamic rather than static. b. They are based exclusively on observations. c. They cannot be modified, once accepted by the scientific community. d. They are universally true. 3. An inference is most closely associated with which of the following? a. A scientific law. b. An explanation. c. A factual statement. d. A prediction. 4. Ptolemy is credited with which of the following? a. Establishing a model for an earth-centered universe. b. Inventing the first telescope. c. Developing a model for a solar-centered planetary arrangement. d. Observing other galaxies in the universe. 5. Which scientist was responsible for explaining the motion of planets, based on mathematical principles? a. Galileo. b. Pasteur. c. Rutherford. d. Newton. 6. The work of Wegener could be used to explain which of the following? a. Earthquakes. b. Tides. c. Comets. d. Solar flare-ups.

Methodology and Philosophy

9

7. Atomic bombs involve which of the following type of reactions? a. Oxidation. b. Chemical. c. Fusion. d. Fission. (Answer Key: 1.d, 2.a, 3.b, 4.a, 5.d, 6.a, 7.d) Works Cited Rutherford, F James and Andrew Ahlgren. Science for All Americans. New York: Oxford University Press, 1990.

Chapter 2

MATHEMATICS, MEASUREMENT, AND DATA MANIPULATION Nate Carnes

The reliance on empirical data is one of the hallmarks of science. In fact, it is one of the essential components of the nature of science that is used to observe and make claims about natural phenomena (Lederman & Lederman, 2004; McComas, 2004). As a result, an observer needs some understanding and ability in applying mathematical skills with particular regard for measurement and data manipulation issues. This chapter addresses processes and issues related to the use of mathematics, measurement, and data manipulation skills that middle level science teachers must know and be able to apply.

scientific MeasUreMent and notation systeMs Scientists all over the world typically use a metric system that is called the International System of Units, abbreviated as SI. Use of this standardized system allows them to compare their work with others and to communicate their results in a “common language.” Specifically, they use SI units to measure length (in meters), mass (in grams), and volume (in liters). The length of a table might be one meter long, an object might have a mass of 10 grams, and a thirsty soccer player might drink one liter of water over the course of a match. Additionally, there are units for measuring temperature and time. The SI makes data collection and manipulations far easier to use than the English system that consists of feet, pounds, and gallons. The SI is comparable to the money system in the United States in that it is based on ten and multiples of ten. To make data measurements less cumbersome, dif-

Mathematics, Measurement, and Data Manipulation

11

ferent graduations of a unit can be used. For example, a student might use meters (m) to determine how far a water-powered car travels across the school yard. However, it would be more appropriate to use millimeters (mm) to measure the length of some small insects found in the school yard. Some common prefixes that are used with metric units appear in Table 2.1. The prefix provides a clue for the size of the unit. For example, a millimeter (mm) means one- thousandth (1/1000) and is one thousandth of a meter. Stated differently, it takes one thousand (1000) millimeters to make a meter. Therefore, 1000 millimeters is equal to 1 meter. In another example, one kilogram (kg) is equal to one thousand grams (g). Table 2.1 provides different representations of 3,120 meters (3,120m). Table 2.1 Some common prefixes used in the metric system.

Prefix Abbreviation How to Say the unit Gima G Gimameters Mema M

Memameters

Kilo Deka Deci Centi Milli Micro

kilometers dekameters decimeters centimeters millimeters micrometers

k da d c m µ

Example

Conversion Factor

.000003120Gm 1 X 109 or 1,000,000,000 .003120 Mm 1 X 106 or 1,000,000 3.12 km 1 X 103 or 1000 312 dam 1 X 10 or 10 31,200 dm 1 X 10-1 or .1 312,000 cm 1 X 10-2 or .01 3,210,000 mm 1 X 10-3 or .001 3,210,000,000 1 X 10-6 or .000001 µm

To change from one size of a unit to another, an individual needs to simply multiply or divide by multiples of ten. Consider the sample problem below: Convert 97 cm to meters. Step 1: Determine the relationship between cm and meters (100 cm= 1 meter). This means that there are 100 centimeters in each meter. This is the conversion factor. Step 2: In this case, the smaller unit must be converted to the larger unit. Divide by 100 to get the answer. Solution: 97 cm divided by 100= 0.97 meters.

12

Mathematics, Measurement, and Data Manipulation

There are circumstances in which scientific measurements can become cumbersome because of very large or very small values. Imagine a collection of data that includes a number like 153,000,000 kilometers (km). In another circumstance, the data might consist of very small measurements like 0.000000084g. Not only does the writing of these values become tedious, but numbers that contain a lot of zeroes can lead to calculation or recording errors. To make matters simpler, scientific notation is used. Using the first example in this paragraph, 153,000,000 can be written as 1.53 X 100,000,000. Better yet, this same number can be written as 1.53 X 108. In this example, 1.53 is called the coefficient. The smaller number that is elevated to the right of the number 10 is the exponent or “the power of ten” that indicates the number of times the decimal point should be moved. It is the shorthand way of writing a very large number. In this particular case, the decimal point should be moved eight places to the right. By the way, the number is read as: “one point five three times ten to the eighth power.” In cases in which a coefficient has an exponent of one, the value is only multiplied by ten (i.e. 2.0 X101). Generally, there is no distinct advantage to using scientific notation for a number of this size. For very small numbers (i.e. 0.000000084g presented in the previous paragraph), negative exponents are used. So, 0.000000084g can be written as 8.4 x 10-8. The presence of a negative exponent indicates that the decimal point should be moved eight places to the left in this case. This number now reads as: “eight point 4 times ten to the negative eighth power. The exponent can be expressed as a fraction with “1” as the numerator. For instances in which the exponent is zero (i.e. 100), there are no zeroes or a value of ten that follow the stated value (i.e. 9.5 X 100). Therefore the answer is always “1,” regardless of the value that is multiplied by this exponent. Scientific notation can make mathematical operations and the reading of data tables simpler.

scientific data collection, ManiPUlation, interPretation, and Presentation In the business of science, it is important for investigators to distinguish between observations and inferences. Observations result from the use of one or more of the five senses to collect information and may include qualitative and/or quantitative measurements. Generally, the sense of taste is avoided in scientific investigations even in cases in which the investigator is using commonly known substances or materials. On the other hand, inferences consist of interpretations and require mental activity that extends beyond observations. A traveler may observe that grasses in the northeastern part of the United States may grow taller than most grasses in the southeastern part. The traveler may construct this observation by measuring various samples of northeastern and southeastern samples of grasses and uses his/her sense of sight in making these measurements. An explanation for why grasses from these regions grow to differ-

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ent heights would be considered an inference. The distinction between observations and inferences can help gain an understanding that science is more subjective than generally thought. During the collection of scientific data, the consideration of what constitutes the number of significant digits in a set of data or calculations is important. The degree to which an investigator can record information determines the number of significant digits in a measurement. For example, 15 has two significant digits, 15.7 has three significant digits, and so on. The number of significant digits is based on the degree to which an experimenter is able to acquire the data. So, a middle school student may determine the mass of a rock to the nearest tenth of a gram because a triple beam balance allows him/her to do so. Stated in another way, the student may find that a rock has a mass of 15.8g only if the measuring device has the capacity to measure to the tenth of a gram (a decigram). This may be the case if the student uses an electronic balance; most balances that are used in middle school classrooms allow the experimenter to calculate mass to the nearest gram. Similarly, another middle school student may find that a cart in a force and motion investigation travels 235 centimeters or 2.35 meters. In either case, the measurement contains three significant digits. With regard to circumstances in which a measurement contains at least one zero, the following considerations must be made: a. Zeroes placed before non-zero digits are not significant; 0.078 meters only has two significant digits. b. Zeroes placed between non-zero digits are always significant; 5009 kg has four significant digits. c. Zeroes placed after non-zero digits but behind a decimal point are significant; 4.80 mL has three significant digits. d. There are at least two significant digits in 1700 meters, although there may be three or four, depending on whether or not the distance was measured to the nearest meter. Zeroes at the end of a number are only significant when they appear behind a decimal point as in the third case. The assumption is that the experimenter was able to obtain a measurement to that particular degree of specificity. In the third case above, the experimenter seemed to be able to obtain the amount of liquid to the hundredth of a milliliter (mL). Otherwise, it is impossible to tell if the zeros are significant or just serve as a placeholder. For example, in a measurement of 3,700 meters, it is not clear if the zeroes are significant or just placeholders. The number of significant digits in an answer to a calculation will depend on the number of significant digits in the given data of an experiment or investigation. For example, a middle school student measures a block of wood and determines that the height, width, and length each has a measurement of 2.5 centimeters (cm). In order to find the volume of the cube, she must multiply each dimension. Using a calculator, she finds that the volume equals 15.625 cm. Because her measurements were only precise to the nearest tenth of a centimeter, her answer should be rounded to the nearest tenth of a centimeter.

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Therefore, the volume of the cube should be 15.6 cm. Her calculated answer should be no more precise than the measurements that she was able to make. In another case, an experimenter may gather data in which there are different levels of precision. For example, he may find that an insect has a mass of 2.8 grams, using a triple beam balance. In another case, he determines that the mass of a second insect of the same species has a mass of 2.48 grams, using an electronic balance. What would be the total mass of the insects? When adding the insects’ mass together, it is important to remember that the number of significant digits in the answer is determined by the measurement that is least precise (2.8 grams in this case). Therefore the acceptable total mass is approximately 5.3 grams. With regard to developing a plan to collect, manipulate, and interpret scientific data, some middle school science textbooks advocate a specific scientific method. However, there are a variety of approaches that an investigator might use. For example, an investigator might begin with a hypothesis that is based on a series of observations and explains the relationship between two or more variables. Another investigator might identify a problem to investigate with an intent to construct a hypothesis after the collection of data. While there is not a standard sequence for planning and implementing an experimental design, it is important for an investigator to develop and carry out a “fair test.” This expectation is accomplished by paying strict attention to controlling factors (also known as variables). To test a stated hypothesis, an investigator might plan an experiment by giving attention to factors that might influence the outcomes of the investigation. The goal is to design and conduct the experiment in a way that provides insight into how one factor impacts another. These factors may be called variables, also. There are generally three categories of variables. The manipulated variable, also known as the independent variable, is controlled by the experimenter to determine its impact on the results of the investigation. In an experiment in which a middle school student seeks to determine if the number of bulbs in a series circuit impacts their brightness, the number of bulbs would be considered as the independent variable. The brightness of the bulbs would be the responding or dependent variable. So, dependent variables are influenced by the independent variable. There is also a group of variables that could impact the results of an experiment but they are controlled in a way in which they have no bearing on the findings. Let’s say that a student wants to find out if the size of a wheel has any effect on how fast that cart rolls down a ramp. She must plan to use wheels of different circumferences (independent variable) to determine how fast the cart travels (dependent variable) for each trial or attempt. At the same time, other factors that might influence her findings (i.e. mass of the cart, aerodynamics of the cart, mass of the wheels, surface on which the cart travels, or angle of the ramp) should be kept the same throughout the investigation. Appropriate interpretations of scientific data are based on patterns or trends. Do the data show an increase or decrease? For example, a student observer might notice that a particular plant grew 0.2 cm to 0.3 cm each week over a two month

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period in response to a particular brand of fertilizer. The consistency in growth likely supports a claim that the fertilizer makes a positive impact on the plant. When the pattern of data is inconsistent with the tested hypothesis or inference, the investigator should modify his or her claim based on the information that s/he obtained. Alternatively, s/he may repeat the investigation to gain better confidence in what the experiment shows. In cases in which there is no pattern in the data, it is difficult to offer an explanation or claim. Communication of research and findings is an important part of the scientific enterprise. Graphs serve this purpose and are used to organize and display data. An investigator may use any one of at least three different types of graphs. Specifically, a line graph is well suited for displaying contiguous data, information that is collected over a period of time and in an unbroken sequence. For example, an investigator may wish to show how much a plant grew over a period of nine weeks (as shown Figure 2.1). A line graph lends itself well to a display that shows how an independent variable, also known as a manipulated variable, impacts a dependent variable (or responding variable).

Effect of a Fertilizer on Plant A 8

Increase in Plant Height (cm)

7 6 5 4 3 2 1 0 1

2

3

4

5

Number of Weeks Plant A w/ no fertilizer Plant A w/ fertilizer

Figure 2.1 The line graph above displays the impact that a certain fertilizer had on a particular plant (drawing by Nate Carnes)

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Line graphs consist of an X axis that runs in a horizontal direction and a Y axis that runs in a vertical direction. An individual must decide how to number each axis in a way that the numbers are the same distance apart from each other and have consistent intervals between them, forming a scale in each case. Usually, the scale for the independent variable of an experiment is placed on the X axis while the scale for the dependent variable should be placed on the Y axis. If a student conducted an experiment to determine the effect that the length of string had on the number of times that a pendulum swung in a minute, a scale for the varying lengths should be placed on the X axis. The scale for plotting the number of swings should be placed on the Y axis. Each axis should be long enough to accommodate all of the data points. The intervals on a scale should be consistent within itself, although the scales on either axis do not have to be identical to each other. The scales that appear on rulers serve as great examples of consistency and the manner in which the intervals are uniform. To ensure clear communication of the results, there should be labels on each axis that help the reader understand what the values mean. The title of the graph is analogous to a book title; it should give the reader a general sense of the data that is represented (as shown in Figure 2.1). Data points are plotted on a line graph, using the scales on the X and Y axes as coordinates. For example, based on the graph in Figure 2.1, you will notice that the plant with fertilizer grew four centimeters during the third week of the investigation. Typically, the points are connected to highlight how one datum (singular form of data) point relates to another. At the high school level and in professional science communities, a line of best fit is drawn to show the trend of the data. It also helps the experimenter and others who read the graph to determine the relationship between the independent and dependent variables. When drawing a line of best fit, all of the data points do not need to touch the line. The goal is to draw a straight line in a way that all of the plotted data are as close to it as is possible. A bar graph is useful for displaying discrete data, information that is collected in categories that do not suggest a continuum. For example, an individual may want to provide a visual summary of different eye colors that his/her classmates have in a study of genetics (as shown in Figure 2.2). The categories (eye colors in the case of this example) are typically listed across the X axis and the frequency along the Y axis. Alternatively, the categories can be listed along the Y axis with the frequency along the Y axis. Pie charts constitute a third category. This type of graph is used to present data as part of a whole, displaying percentages. For example, it might show the percentage of plants, animals, and fungi that some middle school students found within a certain ecosystem (as shown in Figure 2.3). Distinct from the previous types of graphs, pie charts do not require the construction of an X or a Y axis. In all cases, the graphs are symbolic representations of the data they represent.

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Eye Color of Students in Class A

Eye Color

Other

Green Females Brown

Males

Blue 0

5

10

15

20

25

30

35

Percentage of Class

Figure 2.2 The bar graph above summarizes the number of male and female students in a middle school classroom with respect to their eye color (drawing by Nate Carnes)

Investigation of an Ecosystem Other

Fungi

Animals

Plants

Figure 2.3 The pie chart above summarizes biotic material found within a particular ecosystem (drawing by Nate Carnes)

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interPreting and drawing conclUsions froM data As indicated at the beginning of this chapter, one of the major goals of science is to carefully construct and interpret conclusions from data, including those presented in tables, graphs, maps, and charts. To accomplish this goal, it is important to determine whether or not there is a pattern that exists in the data. In cases in which there is no consistency in the data, it is sometimes difficult to establish a claim, particularly when the investigator seeks to determine whether or not one variable has an effect on another. Sometimes, the final judgment may be that there is no relationship between two variables. In cases in which there is a consistent pattern in the findings, the investigator should draw a conclusion that is clearly connected to those data. Let us consider the data represented in the line graph in Figure 2.1, summarizing the effect that a certain fertilizer has on the growth of a particular plant. The data displayed on the line graph show that Plant A that was placed in soil with fertilizer outgrew Plant A that had no fertilizer over a period of five weeks. Because the dependent variable increased in value as the independent variable increased, the investigator can conclude that there is a positive relationship between the two variables. Whenever the dependent variable decreases in value as the independent variable increases or vice versa, the investigator can conclude that there is an inverse relationship between the two variables. In elementary school, students often receive instruction to connect the data points on the graph with a line. This practice helps them to see the relationship between data points. In high school and in the science community, investigators often draw a line of best fit. A line of best fit is a straight line that is drawn through a set of data to best represent a positive or an inverse relationship between the independent and dependent variables. It helps in making this determination because it slants upward or downward when reading the graph from left to right. Cases in which the line of best fit slants up indicate a positive relationship between the two variables. On the other hand, the line of best fit slants downward in instances in which there is an inverse relationship. In either case, the investigator cannot make conclusions about the impact of other factors, unless there are data that support such claims.

identifying soUrces of error in data Middle school students may say that a certain value for a particular measurement is "right" or "correct." Given the tentative and subjective aspects of the nature of science, it is more appropriate to determine if a particular measurement is precise and accurate. Precision is related to the exactness of the measurement. For example, a measurement of 10.1 cm is more precise than 10 cm. In addition, when an investigator measures an object or obtains data in a precise manner, s/he is likely to get the same measurement throughout repeated trials (the same finding every

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time). Consider an example in which a student drops bean bags in an oversized coffee can from a second story balcony. The degree to which the bean bags land in the same spot indicates the precision with which they were dropped regardless of whether or not they land in the coffee can. On the other hand, accuracy is the degree to which the data matches true values. Data collection methods that lack accuracy often become sources of error. Returning to the bean bag example in the previous paragraph, each time the bean bag lands inside of the coffee can, the "drop" can be considered an accurate one. To avoid errors in accuracy, it is important for the investigator to exercise caution when making measurements. For example, s/he should consider whether or not the end of the ruler is worn when determining the length of different objects. If the beginning of the scale is right at the end of the rule, more accurate measurements can be obtained by starting at some point on the ruler (i.e., the 1 cm mark). At the same time, the investigator will need to account for this alternative starting point. For example, the investigator may measure a piece of string, placing one end of it at the 1 cm mark. The total length must be subtracted by 1 cm to get the actual measurement. In finding the mass of a particular object, it is important to zero the balance first. This precaution requires the investigator to confirm that the pointer points at zero or swings at equal distances on either side of the zero before finding the mass of any particular object.

Figure 2.4 Simplified illustration of a meniscus in a glass graduated cylinder (drawing by Nate Carnes)

Liquids in glass containers tend to curve at the edges and dip in the middle, forming what is called a meniscus (as shown in Figure 2.4). Inaccurate readings of liquids within graduated containers (i.e. measuring cups, graduated cylinders) can result from parallax. It is the apparent measurement or difference in measure-

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ment that results from looking at the amount of the liquid from different viewing positions. When determining the volume of liquid, the investigator must be eye level with the scale on the measuring device (i.e. beaker or graduated cylinder) to determine where the bottom of the meniscus rests on the scale. In some plastic containers, the meniscus may be absent.

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review QUestions—cHaPter 2 1. A certain rock sample has a mass of 5.65 g. Three measurements of the same sample produced the following data: 5.60 g, 5.71 g, and 5.75 g. Which of the following statements is most correct concerning these measurements? a. The data are accurate and precise to the nearest one hundredth. b. The data are accurate but not precise. c. The data are inaccurate and not precise. d. The data are inaccurate but precise to the nearest hundredth. 2. The disc of our Milky Way Galaxy is thought to be approximately 100,000 light years in diameter. One light year is approximately 9,500,000,000,000,000 meters. Which of the following responses best represents the diameter of our galaxy in meters? a. 19.5 x 1018 meters. b. 9.5 x 1020 meters. c. 9.5 x 1015 meters. d. 1.95 x 1020 meters. 3. What fraction of a gram does a milligram represent? a. 1/1000th of a gram. b. 1/10th of a gram. c. 1/100th of a gram. d. 1/10,000th of a gram. 4. The distance from Pluto to the Sun is estimated to be 5.9 x 1012 meters. This distance may be written as a. 5.9 x 1012 meters. b. 5.9000000000000 meters. c. 5,900,000,000,000 meters. d. 59,000,000,000 meters. 5. An investigator seeks to measure the length of a root tip taken from a plant, using a meter stick that has millimeters as its smallest unit. The actual length of the root tip falls more than halfway between 2.5 cm and 2.6 cm. What should the investigator record as the length of the root tip? a. 2.5 cm. b. 2.55 cm. c. 2.6 cm. d. 2.60 cm.

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6. An investigator seeks to obtain the most accurate mass of a mystery powder placed on a paper filter. Which of the following procedures should s/he undertake? a. Measure the sample at least three times. b. Place the triple beam balance on a level surface. c. Subtract the mass of the filter paper from the total mass. d. Wait until the triple beam balance is completely still. 7. How many significant digits are in 860.001grams? a. Three. b. Six. c. Seven. d. Unknown. 8. A beaker that holds 8700 mL of water would be equal to a container that holds a. 8.7 liters. b. 87.0 liters. c. 0.87 kiloliters. d. 8.70 dekaliters. 9. A student determined that there were 37 mL of water in a glass graduated cylinder, even though the actual volume was equal to 36 mL. The inaccurate reading may have been due to a. failing to read the bottom of the meniscus. b. failing to read the top of the meniscus. c. over reliance on only one reading of the scale. d. poor interpretation of the scale of measurement. 10. Which data set is most suitable for constructing a bar graph? a. Number of people with a certain eye color vs. their chronological ages . b. Number of cubs within a wolf pack with a certain eye color. c. Percentage of animals within an eco system who are herbivores. d. Percentage of bodyweight a bear eats before hibernating before winter. 11. Which of the following scenarios best represents a positive relationship between the independent and dependent variables? a. Amount of sunlight during the growing season vs. height of a certain plant. b. Height of a certain plant vs. amount of sunlight during the growing season. c. Speed of a cylinder rolling down a ramp vs. temperature outside the room. d. Temperature outside the room vs. speed of a cylinder rolling down a ramp.

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12. In a certain experiment, an investigator seeks to determine whether or not the size of the pendulum bulb affects its period. After several trials, the number of swings remains the same. What can the investigator conclude? a. The length of string has no effect on the period of a pendulum. b. The size of the bulb has no effect on the period of a pendulum. c. More than one factor affects the period of a pendulum. d. The results are inconclusive and more data are needed. 13. In a contest, a few middle school students found that a male tree frog hopped 548 cm in one leap. A female tree frog of the same species jumped .557 m. Which tree frog leaped the greatest distance? a. Both distances are comparable. b. The data are inconclusive. c. The female tree frog. d. The male tree frog. (Answer Key: 1.c, 2.b, 3.a, 4.c, 5.c, 6.c, 7.b, 8.a, 9.a, 10.b, 11.a, 12.b, 13.d) Works Cited Lederman, N.G.& Lederman, J.S. (2004). “Revising instruction to teach the nature of science:modifying activities to enhance student understanding of science.” The Science Teacher 36(4):36-39. McComas, William F. (2004). “Keys to teaching the nature of science: focusing on NOS in the science classroom.” The Science Teacher. 24(4): 24-27.

Chapter 3

LABORATORY PROCEDURES AND SAFETY—PART I Patricia Bricker

The National Research Council (1996, 2006) and the National Science Teachers Association (2000, 2007) emphasize the crucial role of hands-on laboratory and field investigations in science education. By their nature these investigations create potential for injury. It is the responsibility of science educators and their school systems to ensure that appropriate equipment is available, that materials are safely used, and that appropriate safety and emergency procedures are in place. The recommendations that follow are compiled from a range of sources, including the National Science Teachers Association (2000, 2007, 2008) and the Council of State Science Supervisors (2012).

safe PreParation, storage, Use, and disPosal of laBoratory and field Materials In science education we use a variety of laboratory and field materials that need to be safely prepared, stored, used, and discarded. Common materials to consider include live animals, animals for dissection, plants, and chemicals.

live aniMals

The use of live animals in K-12 science education can help students learn about the natural world. The ethical, responsible care of animals is important in order to protect both the animals and the students. Teachers should use quality sources to learn about proper acquisition and care of specific species, being sure to follow laws and regulations and to take into account student allergies and fears.

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Before acquiring animals, teachers should develop a plan for both short and long term care and/or disposal of animals. Animals should be acquired from reputable suppliers and wild animals should not be used in classrooms because they might spread disease or cause injury. Similarly, animals should not be released into non-indigenous environments. Before acquiring animals, teachers should establish and clearly explain and demonstrate guidelines to promote humane care. Cages should be adequate sizes and kept clean and student contact with animals should be organized and supervised. Classroom activities should involve students in observations and responsible care and limit experimental procedures if they are likely to harm the animals. Hands should be washed before and after handling animals, bites and scratches should be promptly reported to the school nurse and principal, and veterinarians should investigate any unexpected illnesses or deaths.

aniMals for dissections

Animal dissections can help students develop observation skills, discover animal anatomy and physiology, and appreciate animal life. Dissection activities require appropriate planning and supervision to be successful. Teachers should be sensitive to diverse views about dissection and provide alternative activities for students that do not feel comfortable participating. Specimens should either be purchased from a reputable scientific supply company or an FDA-inspected facility such as a supermarket or butcher shop. Salvaged specimens should not be used. The room should have appropriate ventilation and lighting and all people in the room should have gloves, goggles, and aprons. Teachers should instruct students in the proper use of dissection tools such as scissors, scalpels, and tweezers. Specimens should be handled respectfully and disposed of properly. A typical disposal procedure for preserved specimens is to thoroughly wash away preservatives, drain, and double bag for normal garbage disposal. However, teachers should check with local water treatment facilities to ensure compliance with rules and regulations regarding disposal of formaldehyde solutions.

Plants

Learn in advance about any plants you plan to use in your classroom, as some can be highly toxic (CSSS 2012). Ask in advance about student allergies associated with plants and do not use any poisonous or allergy-causing plants. Teachers and students should handle plants with care and wash their hands thoroughly after handling them. Teachers should make a clear distinction between edible and nonedible plants. While plants should not be eaten in the lab, edible plants can be eaten outside of the laboratory setting with clear guidance from the teacher. Wild plants should not be picked unless there is a specific reason to do so.

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cHeMicals

A Material Safety Data Sheet (MSDS) should be on file and easy to access for all chemicals (CSSS 2012). The MSDS provides information about proper storage and recommended protective equipment such as goggles, aprons, and gloves. When possible, keep chemicals in the original manufacturer’s containers in order to assure proper labeling information. Otherwise, all chemicals should be labeled in a clear, easy to read fashion with the following information: (a) chemical name, (b) chemical concentration, (c) date received or put in container, and (d) hazard information and handling precautions. Chemicals should be stored in a designated area that is separate from the classroom space. The area should be marked with appropriate warning symbols and have both proper ventilation and fire extinguishers. Storage shelves should be securely attached to the wall and each shelf should have a lip to stop bottles from sliding off shelves. It is important to divide chemicals into organic and inorganic and then follow National Institute for Occupational Safety and Health/Occupational Safety and Health Administration (NIOSH/OSHA) guidelines regarding the separation of incompatible chemicals. Proper disposal of chemicals is essential and information on the MSDS sheets should be followed. Generally speaking, the Environmental Protection Agency and the American Chemical Society suggest the following methods: (a) send to sanitary landfills, (b) use hazardous waste landfills, (c) put in sewer system, (d) incinerate, (e) recycle or reuse, and (f) employ chemical, physical, or biological treatments such as neutralization, oxidation, precipitation, and solidification. The appropriate choice will depend upon the chemical to be disposed and local resources and regulations. When in doubt, consult an expert such as a hazardous waste management agency, an EPA office, the fire department, or the state department of education.

aPProPriate laBoratory and field eQUiPMent Appropriate laboratory and field equipment is needed for science investigations. Tools are used for data collection and analysis and include items such as microscopes, graduated cylinders, beakers, rulers, spring scales, balances, thermometers, stopwatches, computers, and calculators. Glassware should be clean, free of chips and cracks, and heat-resistant. Science labs should also be equipped with appropriate safety equipment such as the following (CSSS 2012): (a) eye wash station, (b) fire blanket, (c) tri-class fire extinguishers, (d) first aid kit, (e) safety goggles, (f) protective aprons, (g) gloves (rubber or latex) for dissection, (h) tongs, mittens, and/or aprons for hot or cold materials, (i) sanitizing or sterilizing materials such as alcohol swabs and 10% bleach solutions, (j) smoke, carbon monoxide, and heat detectors, (k) two unobstructed exits to labs, when possible, (l) ground fault circuit interrupters for all electrical outlets, and (m) master shutoff valves or switches.

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In addition to chemicals, the school storage area should have Material Safety Data Sheets and a bucket of kitty litter or 90% sand/10% vermiculite and diatomaceous earth to assist with cleanup of chemical spills. Teachers should keep an up-to-date inventory of all science equipment and classrooms should have prominently posted emergency procedures and telephone numbers. Labs should be inspected regularly and there should be an annual verified safety check.

safety and eMergency ProcedUres Safety in science education needs to be a high priority for all. As stated in the National Science Teachers Association (2000) position statement about safety, school administrators and teachers should share the responsibility of creating and maintaining safety standards. Safety should be a major consideration in planning and risk factors need to be evaluated next to the educational value of activities. Administrators and teachers need to know current safety research and regulations, have appropriate safety equipment on hand, and know how to use this equipment. A consistent local procedure for accidents, injury, or other emergencies needs to be established. General steps might include checking and assessing the scene and taking immediate action to remove the hazard, checking any injured people and deciding on a plan of action, notifying school authorities, calling 911 as needed, caring for the injured parties, and contacting parents or guardians as needed. When the emergency situation is over, events need to be documented. Students need to know about laboratory safety procedures and equipment. The goals should be awareness and safe execution of science activities. Typical safety procedures include the following: (a) follow directions carefully, (b) no eating or drinking in labs, (c) keep tables clear except for necessary materials, (d) pull back long hair and loose clothing, (e) keep chemicals away from exposed skin, (f) turn off hot plates and burners when they are not in use, and (g) avoid horseplay. Students need to know what safety equipment is available, when to use it, where to find it, and how to use it. Recommended strategies for teaching students about safety include written and oral instruction, posted visuals, practice of the emergency plan, consistent teacher modeling, and clear explanations of potential hazards. Students should be held accountable for related information through safety contracts and/or testing. Science activities need to be supervised and safety procedures should be consistently enforced. In the event of an accident, everyone should stay as calm as possible and follow the specific school’s safety plan in a prompt manner. Broken glass is one of the most common accidents. When glass breaks, students should tell the teacher and the teacher should clean up the glass because of potential cuts. In the event of cuts or scrapes, students should once again tell the teacher and let the teacher help the hurt person. Everyone needs to avoid contact with another person’s blood and students should be moved away from an area

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with blood until it is properly cleaned. The school nurse should be informed about cuts and scrapes due to potential infection. All chemical spills should be treated as dangerous. Students should inform the teacher and teachers should consult and follow directions on Material Safety Data Sheets. Sometimes cleanup involves simply wiping up the spill and at other times it can be a dangerous situation that requires additional precautions. When the spill is on a person, procedures might include flushing impacted skin, drenching and/or removing affected clothing, eye washing, and getting medical attention as soon as possible. Additional classroom cleanup methods might include neutralizing spilled acids or bases, spreading diatomaceous earth, sweeping, and proper disposal of remnants. To prevent fires, keep burners off when they are not in use and minimize the amount of paper at lab stations. When fires occur, you should first focus on the safety of people. Pull the fire alarm if people are in danger. If a person is on fire, douse the flames with water in a drench shower when possible. Otherwise, drop and roll the person and smother the flames in a fire blanket. Do not use a fire blanket on a standing person as this will aggravate the situation, not solve it. When materials are on fire, an ABC fire extinguisher may be used. It is important to use gloves for cleanup of body fluids, pathogenic bacteria, or DNA. Pour a disinfectant such as a 10% Clorox bleach solution on the spill and wipe the spill with paper towels. Dispose of the towels in biohazard bags and sterilize contaminated glassware in an autoclave.

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review QUestions—cHaPter 3 1. Before acquiring animals, teachers should do which of the following? a. Assign a research paper about the animal in order to ensure students are properly informed. b. Establish, explain, and demonstrate guidelines to promote humane care. c. Observe the animal in its natural habitat. d. Contact a wildlife specialist. 2. What document should be on file and easy to access for all chemicals? a. National Chemical Data Sheet. b. Proper Storage Guidelines. c. American Science Safety Sheet. d. Material Safety Data Sheet. 3. In what manner should chemicals be stored? a. In cabinets in the classroom. b. At student lab stations. c. In storage areas separate from classroom space. d. In original containers only. 4. Which of the following safety equipment should be included in all science labs? a. Eye wash. b. Smoke, carbon monoxide, and heat detectors. c. First aid kit. d. All of the above. 5. All science equipment rooms and classrooms should have which of the following? a. An assistant to ensure student safety. b. Posted emergency procedures and phone numbers. c. Heimlich maneuver directions. d. All of the above. 6. When an emergency situation is over, the teacher should do which of the following? a. Document the events. b. Immediately dismiss class. c. Revise the lesson plan. d. Inform the school board.

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7. When glass breaks, students should do which of the following? a. Create a buddy system and cleanup the glass. b. Call the janitor to properly dispose of the glass. c. Inform the teacher so he or she can cleanup. d. Properly mark the area to avoid injury. (Answer Key: 1.b, 2.d, 3.c, 4.d, 5.b, 6.a, 7.c) Works Cited Council of State Science Supervisors (CSSS), Science Safety: Making the Connection, accessed October 15, 2012, http://www.csss-science.org/safety.shtml. National Research Council (NRC). America’s Lab Report: Investigations in High School Science. Washington, DC: National Academy Press, 2006. National Research Council (NRC). National Science Education Standards. Washington, DC: National Academy Press, 1996. National Science Teachers Association. “NSTA Position Statement: Liability of Science Educators for Laboratory Safety.” Last modified September 2007. http://www. nsta.org/about/positions/liability.aspx. National Science Teachers Association. “NSTA Position Statement: Responsible Use of Live Animals and Dissection in the Science Classroom.” Last modified March 2008. http://www.nsta.org/about/positions/animals.aspx. National Science Teachers Association. “NSTA Position Statement: Safety and School Science Instruction.” Last modified July 2000. http://www.nsta.org/about/ positions/safety.aspx.

Chapter 4

LABORATORY PROCEDURES AND SAFETY—PART II Matt Seimears

Many teachers face the problem of not knowing what is safe and what policies they should follow when teaching science. Chapter 4 provides several sets of safety guidelines that you may use to structure your science classroom and help ensure the physical safety of your students.

electrical

Figure 4.1 Power Cord (drawing by Annisa Lord)

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The use of electrical equipment is a very important, commonly overlooked aspect of teaching science. The following items will help you understand how to protect your students from electrical shocks. 1. Always keep your lab centers dry and avoid spills around electrical outlets. 2. Make sure all electrical plug-ins include a ground plug (round) and that the plug is clean and has no mildew or discoloration. 3. Always examine cords for exposed or missing wire before plugging in an electrical device. 4. Make sure all plug-ins have a safety reset button (GFI plug) when working around liquids. 5. Make sure students understand that electricity can be very dangerous. 6. Explain to students that they should never use the cord to unplug an object. 7. Tell students about your expectations for using electrical equipment and describe how they will be assessed. 8. Post examples of electrical safety on the classroom walls.

first-aid

Figure 4.2 Science Room With First-Aid Kit (drawing by Annisa Lord)

In case of an emergency, you may need to take action until advanced medical help arrives and it will be helpful to have a first-aid kit available. A well-stocked firstaid kit should include the following supplies: 1. General first-aid instructions 2. Box of Q-Tips 3. Non-latex gloves 4. Eye pads 5. Non sterile pads 6. Band-aids 7. Assortment of adhesive bandages 8. Eye irrigation bottle (unopened)

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9. Gauze rolls 10. Scissors 11. Blot clot packages 12. Antiseptic and antiseptic wipes 13. Thermal blanket 14. Tape 15. Zip lock bags 16. Sponges 17. Butterfly bandages Do’s in First Aid: 1. Do be calm and collected as you assess the situation. 2. Do request assistance if needed. 3. Do provide the injured student with assistance. 4. Do check to make sure the victim is oriented X 3 (victim is aware of person, place, and time). 5. Do write a report. Don’ts in First Aid: 1. Don’t panic. 2. Don’t appear as if you do not know what to do. 3. Don’t try to handle a large scale incident all by yourself. 4. Don’t diagnose. 5. Don’t perform CPR unless you are certified to do so. 6. Don’t try to transport, unless absolutely necessary. 7. Don’t allow the student to leave without consulting a parent.

fire safety

Figure 4.3 Fire Safety Manual (drawing by Annisa Lord)

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Fires can occur in the science classroom in a variety of ways, including improper disposal of chemicals and mishandling of burners. The following items will help you lower the risk of fires in you classroom: 1. Become familiar with the fire safety standards and protocol in your school district. 2. Develop a Fire Safety Manual for your classroom, based on your school district's policies. 3. Review the fire safety rules regularly with your students.

sHarP instrUMent safety

Figure 4.4 Sharp Instrument Safety Check List (drawing by Annisa Lord)

When having students work with sharp instruments, a step by step procedure must be followed. The following items will help you prepare to use sharp instruments in your science room. 1. Keep your lab centers as neat as possible. 2. Make sure all sharp instruments are clean and sharp. 3. Make sure you give thorough instructions for how to use each sharp instrument, using a Sharp Instrument Safety Check List. 4. Help students understand that sharp instruments are not toys and it is a privilege to use them. 5. Provide examples of sharp instrument safety. 6. Develop a plan for how you will deal with the misuse of sharp instruments.

PART II BASIC PRINCIPLES

Chapter 5

MATTER AND ENERGY Adam Johnston

Before delving into the details of matter and energy, it’s important to orient ourselves to what we’re talking about in the first place. Let’s frame it this way: “matter” is stuff and “energy” is what the stuff does or can do. You can pick up matter, arrange it, organize it, and combine it. What kind of matter you have determines whether you have the carbon that makes up a cat or the silicon that makes up a transistor. How much and what kind of energy that matter has determines what the cat or transistor is doing or can do.

tHe strUctUre and ProPerties of Matter Matter, as stuff, comes in lots of different forms. It’s more than just the difference between a cat and a transistor, however. Any matter can have an array of phases or states, including solid, liquid, and gas. For example, water can be found as solid ice, liquid water, or the steam boiling away from a pot of water on the stove. In any of these states, the ingredients of the matter are the same. The water’s chemical makeup is always a combination of hydrogen and oxygen atoms, and these are always combined in exactly the same manner. This combination of hydrogen and oxygen creates a fundamental unit of water that we call a molecule. This particular molecule is what constitutes and defines the compound we call water, regardless of what state it is in. What distinguishes one state of matter from another is the spacing and arrangement in between the individual molecules. Solids, while still mostly empty space, have the least separation between molecules, and the arrangement can have some order or organization to it. Liquids have more space in between molecules,

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and this space is incompressible. Gases have even more space in between molecules and the space is compressible. Unlike liquids, gases can take up greater or lesser amounts of volume when under different amounts of pressure. It’s surprising that in all states (solid, liquid, or gas) most matter is empty space. How, then, does it have any physical substance to it—the material that we can hold, push, and splash? You probably have been introduced to the idea that molecules, the building blocks that uniquely define the smallest stable chemical pieces, are made up of atoms and each atom is made up of protons and electrons. Protons and electrons are electrically attracted to one another, and we model this by describing the protons as positively charged, the electrons as negatively charged, with the rule that “same” charges repel one another while “opposite” charges attract. Because of these forces, we rarely find protons and electrons in anything but equal numbers, since they have the same amount of charge with opposite sign (positive vs. negative), and whenever there is one extra electron or proton in an arrangement of molecules, the excess of one kind of charge will attract the opposite and bring things back into balance. This should all sound unlikely, since none of this is immediately detectable and so much of it is far outside of anything that we can relate to. There are a few things that help give this model some perspective. First of all, the number of molecules in the universe is amazing. In a gram of water, the number of molecules that would fit in one cubic centimeter (imagine your thumbnail’s width making the side of a cube) would be a million times a million times a million times a million, roughly. Secondly, not only are these molecules small, but atoms are even smaller, and their constituent electrons and protons smaller still. They are extremely abundant, and so it’s easy to imagine that in this giant population of molecules that there are electrons being lost, then gained, lost, retrieved, without any really substantial effect on the entire collection. It’s also important to know that the positively charged protons, while just as ridiculously small as they would have to be for so many to fit into that gram of water, are 1000 times more massive than their respective electrons. The electrons, then, are the constituents of matter that are responsible for all interactions. They whirl about in a blur of configurations, but in all cases they are the particles responsible for chemical bonding, interactions between molecules, and even the everyday forces that you experience. Your hands and a table are all made of matter, which we stated earlier was mostly empty space. The electrons protect this empty space, attracted to the protons they are tied to, but repelled by every other electron in the universe. Your very empty space hands don’t go through the very empty space table because the strong repulsive forces of the electrons in each of these give both your hands and the table some structure. Every push, rub, touch, pull, stretch, and contact are due to electrons repelling one another.

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If you are ever in the mood to detect electrons and their interactions a little more directly, you can move them around a bit. When you peel a piece of “invisible” tape (for wrapping gifts) from its roll, you often note that it will have an attraction to your hand or the original roll and two pieces of tape that are peeled in succession will have forces of repulsion from one another. This is a result of extra electrons being peeled from or left behind on the roll. Or, when you rub a balloon on your hair or a wool sweater, you will move excess electrons to the balloon, and you’ll often be able to detect the attraction of the balloon back to the sweater because the excess electrons make the balloon negatively charged, while the sweater will be positively charged because extra electrons have been removed from it. Perhaps the most phenomenal thing about electrons and protons is not that they are oppositely charged, but that they are oppositely charged by exactly the same amount. In standard metric units, we say that each of these has a positive or negative 1.60x10-19 coulombs of charge. The amount and the units don’t matter as much as the fact that this is exactly the same amount for a negatively charged electron as it is for a positively charged proton. This is the smallest amount of charge that nature knows, and it’s fortunate that it comes in these specific quantities, because only in this way can the negatives of the electrons and the positives of the protons all balance out to a net charge of zero, giving atoms and molecules their stable, balanced composition.

factors tHat inflUence tHe occUrrence of tHe eleMents Electrons and protons combine to make atoms, and combinations of atoms make molecules. Each type of atom is described as an “element,” and you are probably familiar with some elements that are organized in the periodic table, such as hydrogen, helium, carbon, nitrogen, and oxygen. Of course, these elements exist not only as individual atoms, but also as combinations of atoms that are molecules. For example, oxygen in our air is generally a molecule of two oxygen atoms. Chemical combinations of different elements make molecules that we refer to as compounds. Water, a combination of two hydrogen atoms and one oxygen atom, is a good example. Most materials that you are familiar with are made of compounds. Each of these molecules relies on the electrons to hold them together (or create “bonds”) as well as define the shape and interactions of the molecules themselves. Each element is uniquely determined by the number of protons, and thus the number of electrons, within its characteristic atom. So hydrogen, the most basic and prevalent atom in the universe, has only one proton at its center, or nucleus, guarded by one attracted electron. Helium is defined as the element whose atom has two protons in the nucleus, while carbon, nitrogen, and oxygen have six, seven, and eight protons respectively. In other words, each unique element is built out of a unique number of protons and electrons. A periodic table of elements dis-

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plays these elements in order of the number of protons for each element, and also organizes elements with similar properties. How can an atom exist with multiple protons in its nucleus if these protons are all positively charged and repelling one another? Another force must exist to make this possible, a force we will refer to as the “nuclear force.” The nuclear force works at incredibly small distances, like those within the nucleus of the atom, to keep these protons attracted to one another. Yet, it doesn’t work at greater distances, like those in between individual atoms.

PHysical and cHeMical cHanges of Matter As you know and experience regularly, the stuff of our universe undergoes change. We have categorized these changes into two fundamental groups—physical change and chemical change. Matter itself doesn’t really care what kind of change it goes through, but it can be helpful for us to make these kinds of distinctions in order to know the details of a given process. A physical change is one in which the chemical structure of some matter does not change. That is, the arrangement of the atoms within a molecule is the same after the physical process. Changes of phase are good examples of this kind of change, where some material may change from a solid to a liquid, a liquid to a gas, or vice-versa. These are substantial changes, but it is only a reorganization of the molecules that are already there, changing their spacing and arrangements. Similarly, merely separating, crushing, or mixing materials does not change their chemical properties. By most definitions, even having materials dissolve into a solution is a physical change, since the material has not recombined into some new chemical compound. Chemical changes are those that do change the chemical composition of some materials. Chemical changes will always happen to at least two different materials, since a change in one is dependent on some contribution from another material. Burning is a common example of a chemical change, in which oxygen is added to some molecules and removed from others. When an acid and base mix, they create a chemical change as well, leaving behind salt and water and a gas in lieu of the original materials, such as vinegar and baking soda. In processes involved in living organisms, such as respiration and photosynthesis, other recombinations of atoms are taking place to form new chemical compounds. Often we look for some telltale signs that indicate a chemical change. These include changes in color, smoking or bubbling, and spontaneous releases or absorptions of energy (e.g., heat or light). These types of changes do not define a chemical change, but are just indications that it is occurring. Chemical changes are defined as those that result in different chemical compounds after the change. Chemical changes are also difficult to reverse. For example, baking a cake, cooking hamburgers on the grill, or combining vinegar and baking soda all display changes that are chemical, and none of these can be undone. Physical changes

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might have energy exchanges as well, such as when ice melts, but these can be reversed, and the chemical composition never changes.

conservation of Mass and energy Of all the principles in science, there may be none more fundamental than conservation of mass and energy. Very complicated problems can be solved and accurate predictions made based on the rules of conservation. At its most basic level, conservation of energy and mass simply states that nothing can be created or destroyed. Therefore, all reactions and processes must have the same sum of mass and energy before and afterwards. The trick is to keep track of this. Many of the basic principles of science are just applications of these conservation rules. For example, chemical processes are often described with chemical formulas that involve balancing the mass and composition on each side. While the details sometimes obscure the principles of conservation, reminding yourself that virtually all scientific phenomena have this commonality will help you make sense of them. The interesting part of these conservation principles is that they hold true in situations for which a lot of complicated processes might be taking place. Let’s take boiling water as an example. Typically, we’d boil a pot of water by placing it on a stove top and turning on the burner. As the flame or other source of heat below the pot is turned on, it is transferring energy to the system of the pot and water. We detect this initially as an increase in the temperature of the water, which is one way that we measure and detect an amount of energy. Later, as energy from the burner continues to be added to the water, the water starts to change its state from a liquid to a gas—the process we call boiling. As the water is boiling, its temperature stays fixed (at 100 degrees Celsius at sea level) as every water molecule in the gas state emerges from a water molecule in the liquid state. So, if you were to measure the mass of the pot of water before it had boiled, and then the sum of the mass of the liquid plus the mass of the gas, the amount would be the same. The same principles hold true for chemical reactions. Take the simple combination of baking soda and vinegar. If you’ve never tried combining these two items, you should try it yourself. The combination of the two creates a chemical reaction that releases energy that originates from energy that is stored in each of the two original ingredients. This release of energy creates fizzing and an increase in temperature. It also leaves behind water, salt, and carbon dioxide (as a gas). Even though these products are different than the chemical composition that we started with, the mass will all be the same. And even though the energy takes a different form in the reaction, it comes from the storage of that same amount of energy in the molecules.

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energy transforMations Energy transformations take many different forms and in all energy transformations the total energy is conserved, but it manifests itself in different ways. You might think of it as a way that nature does its accounting. Instead of using money from a bank account to purchase products of different prices, energy transforms back and forth from potential, stored energy to kinetic, motion energy. The baking soda and vinegar reaction is one example. Energy is stored chemically, and then an equivalent amount of energy shows up in a different form—in this case the motion of the molecules that defines the temperature increases. A more basic example might be of a ball that we can drop from the top of a science building. From six stories above the ground, the ball starts out with no motion, but you know that it has the potential to fall. As the ball loses height, it picks up speed. We observe that the amount of pace the ball gains is the same every time it’s dropped from this height, and we explain this by describing that the ball has the same amount of energy added to it by virtue of the height it gains. A certain amount of height results in a certain speed. If you imagine a child on a swing moving back and forth, you can see this conservation of energy going from the potential energy stored in the height that she rises to, picking up kinetic energy as she picks up speed at the low point, and then transforming from kinetic to potential energy as she rises up to the opposite side. Energy transformations take many different forms, but the conservation of the total energy always holds true. The energy that you use to maintain your body temperature comes from chemical reactions in your body, the source of which is potential energy stored in those chemicals that are converted into usable sugars. Those foods store energy in a variety of chemical bonds that were originally given their energy by the sun and photosynthesis. The energy that comes from the sun originates as nuclear energy in the sun’s core. This energy is transferred to the exterior of the sun, where it radiates as light to our planet (and everywhere else). Plants are able to use this energy to grow and store extra chemical potential energy, and animals, including humans, are able to consume the plants not just as matter, but for their energy. If you eat meat, you’re simply adding one extra step to this process. All of your body’s processes ultimately are indebted to energy that comes from the sun. In the production of electrical energy, we see similar transformations of energy. Electrical energy, such as what you can get when you plug in a toaster into an electrical outlet, originates from a source that is not originally electrical. Much of the production of electricity that we get comes from coal. As coal is burned, a chemical change that transforms stored chemical energy into a kind of kinetic energy shows up as an increased temperature. This energy goes into water, which is boiled, and the rush of steam from this boiled water is used to set a turbine into motion. That turbine’s motion is then used to generate the electricity that you use. In all of these transformations, from the energy stored in the coal to the increased

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temperature and phase change of some water to the motion of the turbine to the electrical energy that you get for your toaster, the total amount of energy is conserved. It’s true that you can “lose” some energy, but only in the sense that it will leave this particular chain. Instead of being truly lost, some energy will just be leaked into other places, such as warming the surrounding air. Nuclear energy is produced in a very similar manner, except that instead of using stored chemical energy (which is dictated by electrons), it starts with energy stored in the nuclei (protons and neutrons) of these materials. Hydroelectric energy starts with the potential energy stored in water at some height. Wind energy harnesses the motion of wind that is ultimately caused by energy from the sun and solar energy uses the sun’s radiation directly to move electrons around and produce the electricity. We could list example after example of energy transformations, each with its own conversions from one form to another. However, the main thing to remember is that all uses of energy have a source, and the amount of energy in one place must be dependent on this source. As you start to think about all of the different kinds of motion energy (a ball rolling, a train moving, wind blowing) you should start to think about the sources of each of these (an increased height, stored chemical energy, solar energy). Instead of seeing nature as a bunch of varied and idiosyncratic processes, keeping track of energy helps us to see nature as a simple balancing act. You get out exactly what is put in.

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review QUestions—cHaPter 5 1. Elements with which of the following properties are the most common in the universe? a. Those with the fewest number of protons. b. Those with the greatest number of protons. c. Those with some intermediate number of protons. d. All elements, regardless of proton number, are equally common. 2. How are gases different from most liquids? a. Gases have fewer numbers of protons in the atoms making them up. b. Gases have greater numbers of protons in the atoms making them up. c. The space between molecules in a gas can be changed, while the space between molecules in a liquid cannot. d. The space between molecules in a liquid can be changed, while the space between molecules in a gas cannot. 3. Photosynthesis is the chemical process in which a green plant uses energy from the sun to store chemical potential energy. Even though you may not know the details of this process, you know that a. There should be more energy going into the plant than what it stores. b. There should be the same amount of energy going into the plant as what it stores. c. There should be less energy going into the plant than what it stores. d. There is no relationship between the energy going into the plant and what it stores. 4. Photosynthesis is the chemical process in which a green plant uses energy from the sun to store chemical potential energy. Even though you may not know the details of this process, you know that a. There should be more mass going into this chemical process than what is produced. b. There should be the same amount of mass going into this chemical process as what is produced. c. There should be less mass going into this chemical process than what is produced. d. There is no relationship between the mass going into this process and what is produced.

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5. You are graphing the temperature of a single chemical substance as a constant amount of heat energy is transferred to it. The temperature rises until a certain moment when it stays constant. The amount of heat energy transferred has remained the same, so you conclude that a. This substance has undergone a chemical change on its own. b. The substance’s mass is spontaneously decreasing. c. Nature’s maximum temperature has been reached. d. This substance is undergoing a physical change, such as a change of state. (Answer Key: 1.a, 2.c, 3.b, 4.b, 5.d)

Chapter 6

HEAT AND THERMODYNAMICS Christine Schnittka

teMPeratUre and tHerMal energy Temperature and thermal energy (heat) are often confused with each other. Temperature is a measure of how quickly the atoms and molecules in a substance are vibrating. For example, the atoms and molecules in a cup of hot coffee are vibrating more quickly than the atoms and molecules in a cup of cold water. Therefore, if you placed a thermometer in the cup of hot coffee, it would register a higher temperature than if you placed the thermometer in the cup of cold water. Conversely, the thermal energy of a substance is the sum of the kinetic energy of all the atoms and molecules in the substance; therefore, thermal energy depends on the temperature and mass of a substance. Suppose you had a cup of hot water and a pan of hot water, both at the same temperature. Even though both containers of water have the same temperature, the pan of hot water would have more thermal energy because its mass is greater. Furthermore, a substance at a high temperature but with a low mass does not have high thermal energy; however, a lake at moderate temperature would have high thermal energy because of the mass of the water.

effects of tHerMal energy on Matter Thermal energy affects matter several ways. One way is that thermal energy causes the density of matter to change. Warmed fluids are less dense and will float on top of cooler fluids. Warmed solids expand, or even melt. Warmed gases are less dense and have less pressure and take up more space. For example, the water

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is colder at the bottom of a swimming pool because cool water is more dense and sinks. Hot air balloons float because the hot air is less dense than the cooler air surrounding it. Sidewalks expand when they get hot in the summertime and crack. Thermal energy can also cause matter to change state. Warmed solids melt and warmed fluids evaporate. Warmed gases can even become plasma. For example, in the sun hot hydrogen and helium gas become a plasma, which is a fourth state of matter. It takes more time to change the density and state of some types of matter because some types retain thermal energy better than others. Substances that retain thermal energy better also take a longer time to absorb thermal energy. If you placed a cup of water and a cup of sand in the same oven, it would take longer for the water to reach the same temperature as the sand. Then, when you removed them from the oven, the water will stay warm longer than the sand. This is because water has a greater heat capacity than water. That is, it has the ability to retain thermal energy longer than the sand, but it also takes longer to absorb that thermal energy. Heat capacity is symbolized by the letter “C” with the units Joules/change in temperature (Celsius or Kelvin). It is the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius or Kelvin. Specific heat is the heat capacity of one gram of substance. Water at room temperature has a specific heat of 4.1813 Joules/g K whereas sand has a specific heat of 0.835 Joules/g K. This means that water will retain thermal energy five times better than sand, but also require five times the energy heat up to the same temperature as sand. This explains why the sand at the beach will be hot to your feet during the day while the ocean water is still cool. At night, the beach sand cools off quickly and the ocean water does not. It is often warmer than the surrounding air! Because of the ways thermal energy interacts with matter, it drives the water cycle, causing water to evaporate from Earth’s surface. It drives plate tectonics, causing volcanoes and earthquakes. It drives the weather, heating up pockets of air and creating wind, low pressure zones, tornadoes, and hurricanes. It even drives ocean currents which bring warm water from the Equator up the east coast of the United States and over to Europe on the other side of the Atlantic.

MeasUreMent and transfer of tHerMal energy Temperature is easy to measure. There are three temperature scales commonly used by scientists. The units for temperature have been arbitrarily invented by various people over the years. The Fahrenheit temperature scale is based on two points, 0°F and 100°F. Using the Fahrenheit scale, water freezes at 32°F and boils at 212°F. Theoretically, the coldest temperature possible, at which no more thermal energy can be extracted, is called Absolute Zero. Absolute Zero has a value of approximately -453°F.

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The Celsius scale is often considered to be more scientific because 0°C and 100°C are not arbitrary points. The temperature 0°C is the freezing point of pure water at sea level, and the temperature 100°C is the boiling point of pure water at sea level. The degrees in-between are divided up equally, and then extrapolated below 0 and above 100. Using the Celsius scale, Absolute Zero is -273.16°C. The Kelvin scale, invented by William Thompson (Lord Kelvin) in the mid 1800s, is based on the Celsius scale, but Absolute Zero is called 0 Kelvin (note that the degree symbol is not used in the Kelvin scale). A degree Kelvin is equivalent to a degree Celsius, so 273 K is the same thing as 0°C and 373 K is the same thing as 100°C. Thermal energy is much more complicated to measure than temperature. In the metric system, thermal energy is measured in calories. One calorie (cal) is equal to the amount of thermal energy that is required to raise the temperature of 1 gram of water 1°C. Since this is a very small amount of thermal energy, we may also use Calories (Cal), with one Calorie equal to the amount of thermal energy needed to raise the temperature of 1000 grams of water 1°C. In some parts of the world, thermal energy is measured in British thermal units. One British thermal unit (BTU) is equal to the amount of thermal energy needed to raise 1 lb of water 1°F. Since one BTU is equal to 252 cal, it is a larger unit. It is relatively easy to measure the amount of thermal energy that transfers from one system to another. The equation for the amount of thermal energy transferred is Q = C m ΔT where Q is the amount of heat transferred, C is the heat capacity of the material through which the energy is transferring, and ΔT is the difference in temperature (in degrees Celsius or Kelvin) between the two substance. If the temperature of your hand is 37°C and a silver tray is at room temperature (25°C) the difference is 12°C. The heat capacity of silver is 0.233 Joules/g °C. If the silver tray has a mass of 500 g then the amount of heat transferred until the tray and your hand are the same temperature is as follows: Q = C m ΔT Q = (0.233 J/g °C) (500g) (12°C) Q = 1398 Joules Thermal energy always transfers from areas of higher temperature to lower temperature, and this can occur in one of three ways—conduction, convection, and radiation. Conduction happens when two substances touch each other. These substances can be solids or fluids. Conductors are materials that allow thermal energy transfer to happen rapidly, while insulators are materials that do not allow thermal energy transfer to happen rapidly. Metals are good conductors, while plastics are good insulators. The conductivity of a material is measured in terms of how much energy that material can transfer each second. For example, silver, which is considered to be the best metal conductor, has a thermal conductivity of 420 J/s m °C. That means that if you have a one meter long piece of silver wire, and it is 50°C at one end and 49°C at the other end, 420 Joules of energy will transfer in a second from the

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warmer end to the cooler end. The conductivity of air is much lower at 0.023 J/s m °C, which is why trapped air is used for insulation. A second type of thermal energy transfer, convection, happens when cooler, denser fluids fall or sink. Fluids can be liquid or gaseous. When this happens, the colder fluids push the warmer fluids up. Warm fluids do not simply rise on their own; they must be pushed up by a sinking, colder fluid that displaces the warmer fluid. Convection is caused by differences in density. This process can result in convection currents which really are just a continuation of the cycle of rising and falling. Convection currents happen in the atmosphere, the oceans, and under the Earth’s crust with hot magma rising to the surface as more dense Earth materials sink. Anything that keeps fluids from flowing rapidly inhibits heat transfer due to convection. Wool clothing and fiberglass housing insulation, with their closely packed fibers, slow down fluid exchange and heat transfer due to convection. The third type of heat transfer, radiation, occurs when thermal energy travels through the atmosphere or empty space in the form of waves. For example, when you sit near a fireplace your face feels warm because the radiation that leaves the fire is absorbed by your skin. When these rays are absorbed, they are converted from radiant into thermal energy and your skin gets hot. To block that heat transfer, all you have to do is stop the rays from reaching your face. Place a book in front of your face and suddenly your face feels cooler. The sun transfers its thermal energy to Earth through empty space. When the radiant energy from the sun hits our atmosphere and the surface of the Earth, it is converted into thermal energy. The black pavement in a parking lot will be hotter than the light colored concrete sidewalk next to it because dark colors absorb more radiation than light colors.

first and second laws of tHerModynaMics The First Law of Thermodynamics states that energy can go from one form to another, but it cannot be created or destroyed. This might seem to go against your everyday experiences because it seems like energy can disappear out of batteries, out of the warm tub of bath water, and out of the hot cup of cocoa on your kitchen counter. In these cases thermal energy is transferred, but it is not destroyed, because the energy still exists somewhere. The Second Law of Thermodynamics states that during energy transfer within a closed system, things always tend to become less orderly. This law is often referred to as the Law of Entropy, because entropy has to do amount of disorder in the system. The sun will eventually convert all of its nuclear energy to electromagnetic energy and burn out. A car battery will eventually convert its chemical energy to electrical and heat energy, and the battery will die. Thus, the Second Law of Thermodynamics describes the downhill flow of energy sources, from very useful to not useful at all.

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review QUestions—cHaPter 6 1. Temperature is defined as the measurement of a. the quantity of heat in a substance. b. an indication of how much kinetic molecular energy is present at a point. c. the average amount of heat in a substance. d. the sum of the kinetic molecular energy in a substance. 2. Which of the following three temperatures are equivalent? a. 100°C, 456°F, 546 K b. 100°C, 212°F, 373 K c. 0°C, 32°F, 373 K d. 0°C, -32°F, 273 K 3. Thermal energy always travels in which direction? a. In an upward direction. b. In a downward direction. c. From higher temperature to lower temperature. d. From colder materials to warmer materials. 4. Conduction is when heat transfers through a. solids, but not liquids. b. substances that are touching. c. metals, but not plastics. d. insulators, but not conductors. 5. Why does a metal bench in the winter feel colder to sit on than a plastic bench? a. Metal is a better thermal conductor than plastic, so heat transfers from your legs more rapidly when in contact with the metal. b. Metals naturally store less thermal energy than plastics because they have a lower heat capacity. c. Metals are naturally colder than other materials that benches are typically made from, like wood or plastic. d. The plastic bench would actually be colder because plastics are good insulators so they trap the cold air and feel colder than metals. 6. Convection is a form of heat transfer that occurs because a. water or other liquids boil. b. heat rises. c. warmer fluids become less dense and naturally rise. d. heat is transferred as fluids move due to density differences.

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7. Radiation is a form of heat transfer that occurs a. in gases, solids, or liquids. b. between two objects that are touching. c. in the vacuum of empty space. d. when heat rises above a candle flame. 8. How much heat is transferred through a silver spoon placed in a pot of boiling water until the end of the spoon is 100°C? The spoon has a mass of 100 grams. The heat capacity of silver is 0.233 J/g °C. Room temperature is 25 °C. a. 582.5 Joules. b. 1747.5 Joules. c. 582.5 J/sec. d. 1747.5 J/sec. 9. The First Law of Thermodynamics states that a. all things tend toward a state of disorder. b. friction slows down objects in motion. c. things in motion tend to stay in motion. d. energy can neither be created nor destroyed. 10. The Second Law of Thermodynamics states that a. all things tend toward a state of disorder. b. friction slows down objects in motion. c. things in motion tend to stay in motion. d. energy can neither be created nor destroyed. (Answer Key: 1.b, 2.b, 3.c, 4.b, 5.a, 6.d, 7.c, 8.b, 9.d, 10.a)

Chapter 7

ATOMIC AND NUCLEAR STRUCTURE John Elwood

atoMic Models and tHeir exPeriMental Bases The idea that the Universe might be composed of fundamental building blocks dates back to the time of the Ancient Greeks, although solid experimental evidence for the idea came only much later. Today, we call such building blocks atoms. People have discovered well over 300 different types of atoms on the earth, but this great variety of atoms can be understood in terms of a very simple atomic model known as the Rutherford Model. The Rutherford Model contains several postulates. Atoms contain a very small, very dense object at their centers known as the nucleus. This nucleus carries a positive electric charge. Atoms also contain negatively charged particles known as electrons. The electrons orbit the nucleus in a very diffuse cloud that is much larger than the nucleus. We know from experiments that the size of the electron cloud is approximately 100,000 times greater than that of the nucleus. To put this in perspective, if your house was the nucleus of an atom, its electron orbits would be large enough to cover most of the United States. The electrons are bound in orbits around the nucleus because of the electrical attraction between the nucleus and the electrons. Remember, objects carrying opposite electrical charges attract one another. The nucleus of an atom is much, much more massive than its electrons. We know from experiments that atomic nuclei are many thousands of times more massive than electrons. This implies that almost all of an atom’s mass resides in the tiny, dense nucleus.

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Rutherford’s Model was developed in the early 20th century and, since then, scientists have made a few discoveries that have helped advance the Rutherford Model further. Among these, the most important is that atomic nuclei contain two types of particles, protons and neutrons (as described above, the protons and neutrons are bound together into a very small, very dense object at the center of the atom known as the nucleus). Additionally, protons have a positive electric charge and neutrons have no electric charge (so they are neutral), and protons and neutrons have approximately the same mass. The Rutherford model is sometimes called a “planetary model,” because the light electrons circle the heavy nucleus on large orbits very much like the light planets of our solar system circle the heavy sun on large orbits. In both cases, the vast majority of the system’s mass is contained within the central object (be it nucleus or sun), and the vast majority of the “moving” within the system is done by the outer objects (be they electrons or planets). In Figure 7.1, we see the planetary model for an atom of helium-4. Notice that the protons and neutrons are clustered into a compact nucleus at the center of the atom. Even so, we are greatly exaggerating the size of helium’s nucleus. Drawn to scale, the nucleus in Figure 7.1 would be so small that you could not see it with the naked eye.

e-

e-

Proton (+ charge) Neutron (no charge) e-

Electron (- charge)

Figure 7.1 Planetary model for an atom of helium-4 (drawing by John Elwood)

So, how do we use this planetary model to explain the hundreds of different atoms found on earth? Since atoms consist of protons, neutrons, and electrons, we get different atoms simply by changing the numbers of protons, neutrons, and electrons that they contain. Let’s examine how this works in a few simple cases. First of all, since protons have a positive charge and electrons have a negative charge, we won’t be able to create a neutral atom unless we use both protons and electrons. More specifically, all neutral atoms must have exactly the same number of protons and electrons.

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With this in mind, the simplest atom has one proton, one electron, and no neutrons. We call this atom hydrogen. What’s the next simplest atom that we might create? We could still use one proton and one electron, but we could also add in a single neutron as well. Is this still hydrogen, or is this something else? When naming atoms, we name them by the number of protons that they contain. This number is known as the atomic number, and any atom with an atomic number of one is known as hydrogen. Any atom with an atomic number of two is known as helium. And so it continues with the naturally occurring elements, on through plutonium, which contains ninety-four protons. Atoms containing a specific number of protons are also known as elements, so we sometimes say that hydrogen is the first element, helium is the second element, and so on. What about our atom containing one proton, one electron, and one neutron? It still has only one proton, so it is still hydrogen. We need a way to distinguish it from our neutron-free hydrogen, however, and we do so by appending a number to its name. The atom with one proton, one electron, and one neutron is known as hydrogen-2, while the atom with one proton, one electron, and no neutrons is known as hydrogen-1. If these numbers seem mysterious to you, note that they correspond to the total number of protons and neutrons within the atom. This total number of protons and neutrons is referred to as the atom’s atomic mass. Hydrogen-2 gets its name from the fact that it contains one proton and one neutron, and therefore has an atomic mass of two. Atoms having the same number of protons but different numbers of neutrons are known as isotopes of one another. Thus, hydrogen-1 and hydrogen-2 are isotopes of one another. In summary, we have the following rules for naming atoms: (a) changing the number of protons in an atom changes what element it is, and hence changes its name and (b) keeping the number of protons in an atom the same and changing its neutron number converts it into a different isotope of the same element. A common practice for identifying atoms is to use the following notation:

Atomic Mass Atomic Number

Element Symbol

The element symbol is a one or two letter identifier for the element, and the atomic mass and atomic number appear as leading superscripts and subscripts 239 Pu while on the symbol. Using this notation, plutonium-239 is rendered as 94 Pu, 1 hydrogen-1 is represented by 1 H. To help you become familiar with this notation, the first nine stable isotopes have been listed in Table 7.1 along with their particle content and names under both naming conventions. Using the simple ideas behind the planetary model, we can understand the hundreds of distinct atoms found on earth in terms of just three building blocks. We can also use our model to accurately predict many of an atom’s chemical and physical properties.

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Table 7.1 Isotope Naming Conventions

NUMBER OF PROTONS 1 1 2 2 3 3 4 5 5

NUMBER NUMBER OF OF NEUTRONS ELECTRONS 0 1 1 2 3 4 5 5 6

1 1 2 2 3 3 4 5 5

ISOTOPE NAME

Hydrogen-1 Hydrogen-2 Helium-3 Helium-4 Lithium-6 Lithium-7 Beryllium-9 Boron-10 Boron-11

ISOTOPE SYMBOL

1 1

H

2 1 3 2

H He

4 2

He

6 3

Li

7 3

Li

9 4

Be

10 5

B

11 5

B

You may be wondering how we know that the planetary model provides a reasonably accurate picture of actual atoms. What about other models? Why not assume that the electrons reside within the nucleus, or that the protons orbit the neutrons, or some other scenario? The answer, of course, is that we use experiments to distinguish models that are more correct from those that are less correct. As an example of this, consider an alternate model of the atom that was popular in the early 1900s. This model, called the “Plum Pudding Model,” proposed that an atom’s positive charge was spread out in a large, low-density “pudding” that was as large as the atom itself. Stuck within this pudding at various points were the tiny, negatively charged electrons. Note how different this point of view is from that of the planetary model. Instead of having the atom’s positive charge concentrated into a very small, very dense nucleus at the atom’s center, it is spread out into a large and uniform positive paste! One very easy way to test the plum pudding model is by firing alpha particles at atoms. Alpha particles are very small, very dense, positively charged particles. Their densities, in fact, are around 1,000,000,000,000,000 (one quadrillion) times greater than those of atoms. One expects, therefore, that an alpha particle fired at a plum pudding atom will pierce right through, much like firing a bullet through a piece of tissue paper. If you carry out this experiment, however, you will find that while some alpha particles do pass right through atoms, others bounce off and come back and hit you! Upon observing this result, in fact, Ernest Rutherford exclaimed, “It was about as credible as if you had fired a 15-inch shell at a piece of tissue paper and it came back and hit you” (Glasstone, 1958, p 93). How do you get something to bounce off of something else that is a quadrillion times less dense? You can’t. There must be something within the atom that has a density and charge comparable to that of an alpha particle. Put another way,

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essentially all of the mass and positive electric charge within an atom must reside in a tiny, extremely dense object. Thus, the plum pudding model is contradicted by experiment, and the planetary model idea of a nucleus is supported.

electron arrangeMent and tHe cHeMical ProPerties of atoMs There is one aspect of the planetary model that we have not yet discussed—the existence of electron shells (also known as electron orbits). Electrons are all negatively charged, and therefore repel one another electrically. If you try to put too many electrons into a particular shell, the repulsion between them will destabilize the atom, and one or more electrons will pop up into a higher shell. When we say “higher” shell, we mean that an electron must have higher energy in order to get into such a shell. It turns out that there is a fixed number of electrons that can be placed into any given shell, and that this number becomes larger and larger as one proceeds to higher and higher shells. For example, the first electron shell can hold only two electrons. The second shell, by contrast, can hold eight electrons, while the third can hold eighteen electrons (consisting of a lower sub-shell of eight electrons and a higher sub-shell of ten electrons). Atoms containing only filled electron shells and sub-shells tend to be very “happy.” What we mean by this is that they are very stable chemically, and don’t have much propensity to react with other atoms. They are happy because they contain just the right number of electrons. Take away one of their electrons, and one of their shells or sub-shells would no longer be filled. Give them an extra electron, and they have no place to put it without opening up a new shell that they weren’t previously using. Both of these changes destabilize the atom, making it more reactive chemically. Consider the first electron shell. It can hold only two electrons, so the atom with two electrons (and hence two protons) has exactly one filled shell. This atom, as discussed above, is known as helium. We expect it to be very stable chemically, and it is. Helium is a gas at room temperature and pressure, and it is extremely hard to get helium to react with anything. It floats around and does essentially nothing chemically, which is why it is safe to fill balloons with it. If we remove just one electron from helium, however, we are left with the same electronic structure as hydrogen, which is a highly flammable gas at room temperature and pressure. Hydrogen is flammable because it is desperately trying to get that last electron back so that it can have a full shell of electrons. When we see hydrogen “burn,” we are seeing nothing more than its frantic attempts to seize this electron from oxygen atoms in the atmosphere. If on the other hand we add just one electron to helium, we are left with the electronic structure of lithium, which is also extremely reactive. These observations lead to a few general rules about elements, and also explain the general structure of the Periodic Table of the Elements. First, elements with completely filled shells and sub-shells are known as noble gases, and tend to be very stable

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chemically. The first three of these are helium (2 electrons—first shell filled), neon (10 electrons—first shell and second shell filled), and argon (18 electrons— first shell, second shell, and lower sub-shell of third shell filled). Helium, neon, and argon are all very non-reactive gases, and in fact argon gets its name from a Greek word meaning “lazy” or “inactive.” The second rule is that elements that need one additional electron in order to completely fill their shells and sub-shells are known as halogens, and are highly reactive due to their tendency to latch onto the electrons of other atoms. Two examples of halogens are fluorine (9 electrons—needs one more to have the same filled shells as the noble gas neon) and chlorine (17 electrons—needs one more to have the same filled shells as the noble gas argon). The final rule is that elements that need to get rid of one electron in order to consist of completely filled shells and sub-shells are known as alkali metals, and are highly reactive due to their tendency to donate electrons to other atoms. Two examples of alkali metals are lithium (3 electrons—needs to lose one electron in order to have the same filled shell as the noble gas helium) and sodium (11 electrons—needs to lose one electron in order to have the same filled shells as the noble gas neon). Consider Figure 7.2, which depicts the electron configuration of the element fluorine. By counting the protons and neutrons within the nucleus, we can see that this is an atom of the isotope fluorine-19. We also note that fluorine’s outer shell is missing one electron. As discussed above, it is fluorine’s desire to fill this shell that makes it so reactive chemically. Note that the nucleus in this figure has been enlarged greatly to make it visible. With electron orbits of the size shown in the figure, a nucleus drawn to scale would be invisible without a microscope. ee-

e-

e-

e-

e-

ee-

Proton (+ charge)

e-

Neutron (no charge) e-

Electron (- charge)

Figure 7.2 Electron configuration of fluorine (drawing by John Elwood)

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We organize the elements according to their electronic structure by placing them in the Periodic Table of the Elements. When we place elements in the Periodic Table, we arrange them into groups (columns) based upon how far away they are from possessing filled shells and sub-shells. Consider Figure 7.3, in which a modern Periodic Table is displayed. Note that our elements having filled shells and sub-shells plus one extra electron [e.g., lithium (Li) and sodium (Na)] have been placed into Group 1 of the Periodic Table. This is the left-most column of the table and, as mentioned above, the elements in this column are also known as alkali metals. Similarly, note that all of our noble gases [e.g., helium (He), neon (Ne), and argon (Ar),] have been placed into the right-most column of the table. Their placement at the ends of rows emphasizes that they have completely filled the shells and sub-shells associated with their rows.

atoMic and nUclear strUctUre and forces Understanding the existence of electron orbits is relatively simple. The positively charged nucleus attracts all of the electrons. The negatively charged electrons repel one another. The competition between these two effects results in relatively large orbits on which the electrons zip about the nucleus. But what holds the nucleus together? Within it are only positively charged protons and neutral neutrons. Electrically, the protons should repel one another, and the neutrons should do nothing. There seems to be no attraction at all within the nucleus, and we might expect the whole clump of protons and neutrons to simply blow itself apart! Experiments have shown that the electric force is not the only force at work within an atom. Protons and neutrons exert another type of force on one another, a very strong force that they feel only when extremely close together. This force is called the nuclear force or the strong force, and is an attractive force strong enough to keep the nucleus from blowing itself apart. The reason that an atom’s nucleus is so tiny, in fact, is that the protons and neutrons within it must be very close together in order to experience this attractive nuclear force. If you tried to make an atom’s nucleus larger by moving its protons and neutrons further apart, the attractive nuclear force that holds it together would decrease in strength, and the nucleus would disintegrate due to the electrical repulsion between the protons. Nuclei do in fact disintegrate in this manner all the time, and we call such disintegrations nuclear reactions. Any nucleus that participates in nuclear reactions is called radioactive. Let’s return for a moment to the house analogy that we described at the beginning of this chapter. In this analogy, the small dense nucleus was the size of a house, and the electrons formed a large cloud of orbits that was roughly the size of the United States. Pushing this analogy further, the nuclear force is well represented by the walls of the house. If you are inside of the house, the walls of the house keep you inside, much as the nuclear force keeps the protons and neutrons

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Figure 7.3 Periodic Table (Source: Eformulae.com—copied with permission)

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within the atom’s nucleus. Once we exit the house, however, we are free to wander off across the country, just as a proton or neutron is free to leave an atom once it steps outside of the nucleus. Let us quickly summarize our picture of the atom. There are long-range electric forces that exist throughout the atom. Such forces cause electrons to repel one another and protons to repel one another, but cause electrons and protons to attract one another. There are also short-range nuclear forces that cause protons and neutrons to attract one another, but only if the protons and neutrons in question are extremely close together. An atom’s electrons are free to orbit in a very large cloud because the nuclear forces have almost no effect on them. The atom’s protons and neutrons are required to be locked up in a tiny nucleus because only then can the attractive nuclear forces save the nucleus from disintegration. Because the electrons repel one another, we must use larger and larger shells as we add more and more electrons to an atom. Each shell or sub-shell has a maximum number of electrons that it can contain, and atoms achieve maximum chemical stability when they contain completely filled shells and sub-shells. We end this section with a brief discussion of atomic size. We know that atoms are small, but exactly how small are they? Experiments show that they have a size of roughly one Angstrom (one ten billionth of a meter). This means that one would have to line up approximately 200 million of them end to end just to produce an atomic chain one inch long. Put another way, if you were to create such a chain by adding one atom to it every second, it would be over a week before you could see your chain with the naked eye, and it would reach only about a foot in length by the end of your life. If you find that small, recall that the nucleus is around 100,000 times smaller yet!

electron arrangeMent and tHe PHysical ProPerties of atoMs Although all atoms have sizes on the order of an Angstrom or two, each particular element has a unique atomic radius. Furthermore, atomic radii display some simple trends that may be understood in terms of our planetary model of the atom. The first trend one observes, which may seem fairly obvious to you, is that each time you begin using a new electronic shell, the atomic radius jumps up significantly. For example, when one moves from helium (2 electrons—first shell completely filled) to lithium (3 electrons—first shell filled plus one extra electron in second shell), the atomic radius jumps from around 50 picometers to just over 130 picometers (each picometer is one trillionth of a meter). Similarly, neon has a radius of roughly 70 picometers, whereas adding just one more electron opens up a new shell, and gives us sodium with a radius around 160 picometers. The next trend is a bit less obvious. If you increase the element number without using new electron shells, the atomic radius decreases. This is because, although we are adding new electrons to our atom, they are going into a shell that isn’t full, and we therefore need not utilize any new electron shells. Moreover, we

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are also increasing the nuclear charge as we increase the element number. Because the nucleus is positively charged, it attracts the electron shells. If we increase the nuclear charge, it attracts the electron shells more strongly, bringing them in closer and reducing the atomic radius. Simply put, for a given number of electronic shells, a more positively charged nucleus will “hug its electrons tighter,” resulting in a smaller atomic radius. These trends may be summarized in the following three simple rules: (a) within a period (row) of the periodic table, atomic radius generally decreases as we move from left to right, (b) within a group (column) of the periodic table, atomic radius generally increases as we move from top to bottom, (c) the most dramatic increase in radius occurs when we add a new electron shell, that is, when we move from the last column (noble gases) to the first column (alkali metals) of the periodic table. Thus far, we have confined our discussion to atoms containing the same number of protons and electrons. Such atoms are electrically neutral, but it is also possible to have an atom in which the numbers of protons and electrons differ. This, of course, will give the atom an electric charge, and we call such charged atoms ions. An atom with nine protons and ten electrons, for example, will be a negatively charged ion. Possessing nine protons, it is still named fluorine, but it has the same electron configuration as does neon. We denote this ion as fluorine-, or simply Fl-. Removing electrons from an atom, on the other hand, will result in a positively charged ion. If you steal one of sodium’s electrons, you turn it into sodium+, or simply Na+. Removing electrons from neutral atoms always requires energy (you are pulling a negative electron away from a positive nucleus, after all), but the amount of energy required to remove an electron varies dramatically from atom to atom. This energy, known as the ionization energy, displays trends opposite to those seen in atomic radii described above.

nUclear reactions and tHeir ProdUcts So far, we have spoken primarily of chemical and physical reactions. There is another class of reactions in which the atomic nucleus changes in some significant way. The protons and neutrons within the nucleus might rearrange into a new configuration, a neutron might change into a proton, or a clump of protons and neutrons might be ejected from the nucleus altogether! Reactions that result in such nuclear changes are called nuclear reactions. It is true that a nucleus can contain an arbitrary number of protons and neutrons, but only certain combinations of protons and neutrons are stable. Any unstable nucleus will attempt to transform itself into a more stable nucleus by undergoing a nuclear reaction. Although many different nuclear reactions are possible, the vast majority of those observed are a result of one of four processes. The first of these is Alpha

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decay. An alpha particle is a clump of two protons and two neutrons (you might recognize this as the nucleus of helium-4). An unstable nucleus can sometimes make itself more stable by ejecting an alpha particle. Here is an example of a nucleus undergoing alpha decay: 241 95

4 Am ⎯ ⎯→ 237 93 Np + 2 He

In the standard notation that we are using, remember that subscripts represent the number of protons in a nucleus (the atomic number) and superscripts represent the total number of protons and neutrons in the nucleus (the atomic mass). Thus, the nucleus on the left-hand side of the reaction above is americium-241, with 95 protons and 146 neutrons (241 - 95 = 146). Note that the right-most nucleus in this reaction is helium-4, the alpha particle. The emission of this particle is what makes this particular decay an alpha decay. A nucleus can sometimes approach stability simply by converting one of its protons into a neutron, or vice versa. Such conversions are called beta decays. Suppose that a nucleus has too many neutrons and too few protons. It then has the option of converting a neutron into a proton, and we call such a conversion betaminus decay (β-). The basic process looks like this:

n⎯ ⎯→ p + e − + ve As you can see, the neutron can’t change into a proton unless it also emits two other particles—an electron (e-), and a neutral particle with a very tiny mass known as an anti-neutrino ( ve ). Of course, this conversion can also go the other way, and we call that process beta-plus decay (β+). As you might imagine, beta-plus decay takes place in nuclei that have too many protons and too few neutrons. It looks like this:

p⎯ ⎯→ n + e + + ve Once again, two extra particles are emitted, but this time they are a positron (e+) and a neutrino (ve). In case you have never encountered a positron (also known as a beta-plus particle) before, it is very much like an electron except that it has the opposite electric charge. In fact, it is “opposite” in other ways as well, and is an example of antimatter. It is the antiparticle of an electron, and a positron and electron will annihilate one another if ever they meet! Note that because beta decays change the number of protons within a nucleus, they change the atom into a different element altogether. Here are examples of both beta-minus and beta-plus decay occurring within nuclei: 192 77

Ir ⎯ ⎯→

192 78

Pt + e − + ve

and 15 8

O ⎯ ⎯→

15 7

N + e + + ve

In gamma decay an unstable nucleus will become more stable simply by shifting its protons and neutrons around. After it does this, it will obviously still

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have the same number of protons and neutrons that it had previously, and will therefore remain the same isotope of the same element. It will have lower energy, however, and this energy must go somewhere. As you might have guessed from the discussions above, the energy goes into a particle emitted by the nucleus. The particle is traditionally known as a “gamma particle” (denoted γ), but you may know it better as the “photon”. It is the smallest chunk of light, and whenever a nucleus emits one without doing anything else, we call it gamma decay. Here is an example of a nucleus undergoing gamma decay: 60 28

Ni * ⎯ ⎯→

60 28

Ni + γ

Note that because the number of protons and neutrons within the nucleus does not change during gamma decay, we need a new way of indicating that the nucleus has been altered. We do this by placing an asterisk (as above) on the nucleus in the less stable configuration. It rearranges its innards, changes into the more stable nucleus, and emits a photon in the process. In fission, large nuclei that are unstable sometimes simply break apart into smaller nuclei. When a large nucleus breaks apart into chunks (and neither of the chunks is an alpha particle), we call the process fission. Here is an example of a fission process: 235 92

U⎯ ⎯→

144 56

Ba +

89 36

Kr + 2n

In this process, uranium-235 splits into barium-144 and krypton-89. Note that this leaves two extra neutrons that are free to fly off and impact other nuclei. When such a neutron hits another uranium-235 nucleus, it can cause it to fission as well, leading to a chain reaction. If one controls the chain reaction, it can be used to generate power in a nuclear reactor. The vast majority of nuclear reactors in the United States use uranium-235 as fuel.

radioisotoPes and radioactivity The probability that a particular type of nucleus (called a radioisotope) will decay in the next second is the same for all nuclei of that type. For instance, all nuclei of iridium-192 have approximately a one in ten million chance of undergoing beta decay in the next second. This doesn’t sound like much but, if we have ten million iridium-192 nuclei (which is a tiny bit of iridium), chances are that one of them will decay in the next second. If we have ten billion iridium-192 nuclei (still a tiny bit; this is only around three trillionths of a gram), on the other hand, we are likely to get around 1000 decays in the next second. We would like to devise a method for measuring rates of nuclear reactions without having to worry about how many nuclei we start with. We do so by introducing the concept of half-life. Given a radioactive sample, the half-life is defined to be the amount of time it takes for half of the sample to decay. Note that the half-life doesn’t care how big our sample is!

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Here’s a quick example to help you understand. The half-life of iridum-192 is approximately 74 days. Suppose that we begin a new year with a 400 gram chunk of iridium-192. On March 15 (74 days later), our chunk of metal will contain only 200 grams of iridum-192, the remainder having decayed to other elements. By May 28 (another 74 days) half of the remaining iridium-192 will have decayed, leaving only 100 grams. Continuing this exercise, we will have 50 grams of iridium-192 left on August 10, and only 25 grams left on October 23. Note that the rate of reaction decreases as our supply decreases. This is characteristic of nuclear decays, and we refer to this fact by saying that radioactive samples decay exponentially. As should be clear, nuclei with short half-lives are intrinsically more radioactive than nuclei with long half-lives. Radon gas (radon-222), for example, is a nucleus that undergoes alpha decay with a half-life of only 3.8 days. This makes it highly radioactive, and radon is in fact one of the biggest contributors to the natural background dose of radiation that people receive.

radioactive dating Because radioactive isotopes have well-defined half-lives, it is sometimes possible to use them to determine how old a sample is. Doing so is called radioactive dating or radiometric dating. To see how this works, let’s turn our iridium-192 example around. Suppose that we knew that the chunk in question started out containing 400 grams of iridium-192. Suppose also that at some later time, we analyzed the chunk, and found it to contain only 25 grams of iridium-192. This would immediately indicate to us that four half-lives had passed since the formation of the chunk (you must cut 400 in half four times in order to get 25). In other words, radioactive dating would tell us that the chunk is 4 x 74 = 296 days old. Note that in order to successfully use radioactive dating, we need to know how much radioactive material was initially present in our sample and must also have a sample that has been “out of circulation” since the radioactive material entered it. We often have samples satisfying both of these criteria, and radioactive dating has proved incredibly useful in a variety of applications.

fUsion There is one remaining type of nuclear reaction that we have not yet discussed. It is called fusion, and it differs from the reactions above in that it requires at least two nuclei to start the process. You might think of fusion as the opposite of fission. Instead of a large nucleus splitting apart into two or more smaller ones, the fusion process involves the joining of smaller nuclei into larger ones. Fusion reactions can release tremendous amounts of energy, and the following fusion reaction is key in powering our Sun: 1 1

H + 11H ⎯ ⎯→ 12H + e + + ve

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Note that two protons have stuck together and then undergone beta-plus decay. This has resulted in a new isotope of hydrogen, hydrogen-2. Within the sun, this process repeats itself and combines with other processes, ultimately leading to the production of helium-4. In its present stage of life, the sun’s main occupation is converting hydrogen into helium. It produces a huge amount of energy as it does so, and we are the grateful recipients of this byproduct! It might strike you that fusion would make the perfect energy source for us here on earth, so why don’t we use it? Because nuclei are positively charged, it is extremely difficult to get them close enough to stick to one another. The sun gets around this problem by using its massive gravitational field to squeeze them together, but we do not have this luxury on earth. Controlled fusion is not a viable energy source on earth today, but progress is being made daily. It is entirely possible that fusion may become our principal energy source within your lifetime.

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review QUestions—cHaPter 7 1. The central postulate of the atomic theory of matter is that a. positive charges can only be found within the nuclei of atoms. b. all matter is composed of fundamental building blocks known as atoms. c. chemical reactions and nuclear reactions are the same because all atoms contain nuclei. d. because atoms contain electrically charged particles, they must be held together by electric forces. 2. Which particles can be found within the atomic nucleus? a. Electrons and neutrons. b. Electrons and protons. c. Protons and neutrons. d. Electrons only. 3. According to experiments, how does the mass of an atom compare with the mass of its nucleus? a. The mass of the nucleus is roughly the same as the mass of the atom. b. The mass of the nucleus is roughly 100 times larger than the mass of the atom. c. The mass of the nucleus is roughly 100 times smaller than the mass of the atom. d. The mass of the nucleus is roughly 100,000 times larger than the mass of the atom. 4. Circle all of the choices below that are true. a. The name of an element is determined by the number of neutrons it contains. b. The name of an element is determined by its atomic number. c. The name of an element is determined by its atomic mass. d. The name of an element is determined by the number of protons it contains. 5. Different isotopes of the same element possess a. the same number of protons but different numbers of electrons. b. the same number of electrons but different numbers of protons. c. the same number of protons but different numbers of neutrons. d. the same number of neutrons but different numbers of protons.

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6. Which of the following statements is true regarding electron shells? a. Electron shells can contain as many electrons as they want, but atoms are happiest when their shells contain certain special numbers of electrons. b. There is a maximum number of electrons that any particular electron shell can hold. Atoms are happiest, and therefore most reactive chemically, when their electron shells and sub-shells are completely filled. c. There is a maximum number of electrons that any particular electron shell can hold. Atoms are happiest, and therefore least reactive chemically, when their electron shells and sub-shells are completely filled. d. None of the statements are true. 7. By considering their positions within the Periodic Table (Figure 7.3), predict which of the following atoms would be expected to have the smallest atomic radius? a. Aluminum. b. Sulfur. c. Silicon. d. Sodium. 8. Which of the following are necessarily true of ions? Circle all that apply. a. The numbers of protons and neutrons within an ion must differ. b. The numbers of protons and electrons within an ion must differ. c. The numbers of neutrons and electrons within an ion must differ. d. Ions must be electrically charged. 9. Circle all cases below in which a nuclear reaction has occurred. a. An atom has lost an electron, and has therefore become positively charged. b. Two nuclei have bonded together by sharing electrons. c. The number of protons within a nucleus has changed. d. The protons and neutrons within a nucleus have settled into a more stable configuration, and the nucleus has emitted a photon as a result. 10. Which of the following is the most accurate description of fission? a. Fission is the joining together of small nuclei to make larger ones, often with the release of free protons. b. Fission is the joining together of small nuclei to make larger ones, often with the release of free neutrons. c. Fission is the splitting apart of large nuclei to make smaller ones, often with the release of free protons. d. Fission is the splitting apart of large nuclei to make smaller ones, often with the release of free neutrons.

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11. Which of the following nuclear reactions is most important in the functioning of stars such as our sun? a. Beta decay. b. Gamma decay. c. Fission. d. Fusion. (Answer Key: 1.b, 2.c, 3.a, 4. b and d are both correct, 5.c, 6.c, 7.b, 8. b and d are both correct, 9. c and d are both correct, 10.d, 11.d)

PART III PHYSICAL SCIENCES (PHYSICS)

Chapter 8

MECHANICS Kenneth King

forMs of Motion Pushing something and seeing it move is one of the first “scientific” interactions children experience. The purpose of this chapter is to help you understand the common strands and patterns that form the foundation of how we describe various forms of motion. While one form of movement is the same as any other form of movement, it is helpful to organize our discussion of motion into a set of categories that have some elements in common.

linear Motion

Imagine a ball rolling across a smooth, level surface or a hockey puck gliding across a level sheet of ice. If there were no forces acting on them, the ball would continue rolling forever and the hockey puck would continue sliding across the smooth surface of the ice. The ball and the hockey puck represent uniform linear motion because, in principle, they keep moving at the same speed in the same direction until something causes them to slow down or stop. In the real world, the ball or puck will change speed or direction when some sort of force acts on them. For example, the friction that is created between the hockey puck and the ice is enough to cause the hockey puck to gradually come to rest after a time, even though it is small.

Projectile Motion

The sort of motion described so far, a hockey puck sliding across the ice or a ball rolling across a level surface, takes place on a flat, level surface. However, when

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a ball is tossed into the air, it experiences a different type of movement. When movement like this takes place, it is referred to as projectile motion. You know from having watched a ball that is thrown into the air that it travels in a gentle curve or arc. It reaches a maximum height off the ground, and then curves back to the ground, following a smooth, curving trajectory. There are two elements of projectile motion that are important to understand. Part of the motion, directed vertically or up in the air, is influenced by the attractive force of gravity on any object that has been launched into the air. The force of gravity causes the vertical part of the projectile’s motion to gradually slow down and then pause instantaneously at the top of the arc. Once it reaches the highest point in its path, it begins to speed up due to the force of gravity acting on it, reaching the same speed when it strikes the ground as it did when it was launched into the air, but in the opposite direction. The other part of the motion, directed horizontally or downrange, is not influenced by the force of gravity. The horizontal movement maintains a constant speed and direction, unless another force, such as friction with the air, acts on it. In Figure 8.1, the arrows represent the speed in the horizontal and vertical directions. The speed in the “up” direction is steadily slowing down, because the force of gravity is slowing it down until it reaches the top of its flight; it then begins speeding up in the downward direction until it strikes the ground at the end of its flight. With only the force of friction acting on it, the horizontal element of the ball’s speed remains will gradually slow down until it strikes the ground.

Figure 8.1 Projectile Motion (drawing by Kenneth King)

circUlar Motion

One easy way to envision circular motion is to imagine a ball on a string, being whirled around in a circular path. An object tends to either remain at rest or travel

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at the same speed in the same direction unless acted on by an external force. With the string pulling on the ball, the ball is prevented from traveling in a straight line. The string exerts a force on the ball, pulling it in the direction of the string, which produces a circular path. The force is called the centripetal force. A satellite in orbit around the earth, such as the International Space Station or the moon demonstrates the same type of motion. In the case of these bodies, there is of course no string pulling on the moon or on the space station; there is only the pull of gravity giving the same effect.

Periodic Motion

Periodic motion has some of the same properties as other forms of circular motion. One of the simplest ways to think about this type of movement is to think about the movement of a pendulum. A pendulum moves back and forth, tracing the same path over and over again. The regularity of the pendulum’s movement explains why it is the basis of many old clocks. The rate of the pendulum’s period—the time that it takes to move back and forth, returning to its starting points— is based on the length of the pendulum itself. You can try this with a swing set. You will find that for a given length of a swing (measured from where it attaches to the overhead crossbar to the seat), the time it takes for the swing to move back and forth one time is the same, regardless of the weight of the child. Changing the length of the swing, however, changes its period. A shorter swing will swing back and forth faster than will a longer swing.

newton’s laws of Motion Isaac Newton, an English scientist from the 17th century, left a number of scientific legacies. Chief among them were his laws of motion. These laws describe how applying forces to objects causes their movement to change. These laws form the foundation of classical mechanics.

first law of Motion

Imagine a hockey puck gliding across a smooth, level and well-polished sheet of ice. If there were no forces acting on it, the hockey puck would continue sliding across the smooth surface of the ice. In fact, if every outside force could be prevented from acting on the hockey puck, it would keep moving forever. This observation is summarized in the statement, “every object remains in a state of constant motion or at rest, unless an external unbalanced force acts on it.” This is the law of motion that describes the movement of the hockey puck described above. The puck remains at rest, unless something sets it into motion, such as a hockey player striking it with a hockey stick. The puck remains in motion, unless some outside force changes its direction or speed. The friction of the ice, though small, is an external force, and will work to slowly change the motion of the puck, gradually bringing it to rest.

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second law of Motion

The second law of motion is most commonly described by the equation F = m x a. The m in the equation refers to the mass of the body. The a represents the acceleration the body experiences, based on the force applied to it. F, the force, represents the size of the push or pull acting on a body. In the simplest sort of straight-line interaction, applying a constant force to an object causes the object to move faster and faster in the direction that the force is applied. The “faster and faster” quality along a straight line represents the acceleration. Acceleration is a change in the velocity of a body. Velocity is more than simply another word for the speed of an object. Velocity has two parts to it, speed and direction. A force applied to a body can cause it to experience acceleration by changing its speed, its direction, or both. Stepping on the gas while driving an automobile is one way to experience acceleration. The sensation of having the seat back pressed against your body is evidence of acceleration in action. Likewise, stepping suddenly on the brakes in an automobile gives you another opportunity to feel the results of an acceleration, though in the opposite direction from that described above. When you make a sharp turn in an automobile, you undergo acceleration as well. The sensation of being pressed against a car door, as the driver, when you make a sudden turn to the right provides the feeling of having the car door pressing against your left side while in the driver’s seat of the turning car.

tHird law of Motion

Newton’s Third Law of Motion is sometimes called the “action–reaction” law. Watching a rocket take off is a simple way to imagine this in action. The action is the hot gases pushing against the top of the engine, while the reaction is the top of the engine pushing back. As a result, the rocket takes off. Another example involves a pedestrian walking down the street. As the pedestrian pushes away from the sidewalk, the sidewalk exerts an equal and opposite force on the shoe.

Figure 8.2 Action-Reaction (drawing by Kenneth King)

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Mass and weigHt Mass is simply the quantity of “stuff” that makes up matter. A person would have the same mass on the Earth as on the Moon, because he or she is made up of the same amount of matter. In science, we measure the quantity of matter present in either grams or kilograms. Kilograms are often preferred, since they are a more convenient standard of measurement. The water contained in a 1-liter drinking bottle has a mass of 1 kilogram. This value is not an accident because the metric system of measurement was organized this way on purpose. Weight is not the same thing as mass, because weight is the pull experienced on the surface of a planet as the force of gravitation acts upon it. An object would have two different weights when compared on the surface of the moon and the surface of the earth, but it would keep the same mass. This is because the force of gravitation on the moon is less, for a given object, than the pull of gravitation for the same object on the earth. Weight is measured in pounds in the standard system. In the metric system used in science, the unit of force is a newton, which is about 1/5 of a pound.

friction Friction deserves special attention as a force, not only because it is so common, but because its role is not often appreciated. Friction is caused by the effect of two surfaces moving against each other. It can be as simple as the roughness of two surfaces coming into contact with another or more sophisticated, such as when the attractive forces between molecules attempt to adhere to one another. In the example above, it was noted that a hockey puck would travel without stopping if the surface of the ice was perfectly smooth and there was no wall to stop the puck from sliding. In the days of Greek philosophers such as Aristotle, this inclination to ignore the effect of friction served as his rationale to declare that the natural state of objects is at rest. Our more informed understanding is represented in Newton’s First Law of Motion, that unless an outside force acts on something, it will either keep moving or remain at rest. Friction was not, in the time of Aristotle, appreciated as a force that opposed motion.

work, energy, and Power Work occurs when a force is applied that causes an object to move. In its simplest form, work is the product of the force applied to an object and the distance that the object moves: work = (force) X (displacement), or W = Fd. Work in science is measured in units referred to as joules. Joules are units of measurement that express the quantity of energy required to produce the displacement of an object being moved.

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Energy is often described as the ability to do work. The use of energy allows us to move things in opposition to the various forces of nature, such as gravitation or against mechanical devices such as the push or pull of a spring. Energy, as you will explore in other chapters, is present during changes in chemical reactions, in moving electric charges, and drives changes in weather and climate. In this chapter, we will introduce the energy associated with carrying out mechanical work on objects. Power is an important concept related to energy. Power is the rate that energy is expended. An example is a helpful way to explain this concept. It takes the same amount of work to lift a bag of groceries from the floor to a table top, whether one does this quickly or slowly. Lifting the bag rapidly generates more power than doing it slowly. Power is measured in a unit called a watt, which represents units of energy (joules) as a function of time (seconds). The energy described in this chapter is often classified broadly as mechanical energy. It is the energy that is used to move objects from place to place. It is also helpful to further examine mechanical energy in one of two related forms, kinetic energy and potential energy. When a bowling ball, for example, is lifted 5 meters off of the ground and placed on a window ledge, it is described as having potential energy because it required work to move it from the ground to the window ledge. That work can be calculated by multiplying the force applied to move the bowling ball by the distance it was raised off of the ground. The work that it generates as it falls equals the amount of energy it takes to raise it to the window ledge. Pushing the ball off of the window ledge causes it to fall toward the ground. The ball gains kinetic energy as it falls toward the ground. Kinetic energy is the energy of motion that an object possesses. The more rapidly the object is moving, the greater its kinetic energy. As the ball falls toward the ground, it reaches its maximum speed at the instant before it strikes the ground. With its maximum speed, it also reaches its maximum kinetic energy.

siMPle MacHines and torQUe The application of forces to set things in motion is at the heart of how simple machines work. A simple machine changes the size or the direction of a force. It does not create energy or make work “easier.” Instead, a simple machine allows the user to make an exchange in the size of the applied force for the distance that it is applied. The increase in the applied force is generally referred to as the mechanical advantage of a simple machine. Figure 8.3 provides a clear model of how the lever works, allowing the user to “exchange” force for distance to apply a large force over a small distance through the use of a pry bar.

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Figure 8.3 Lever (drawing by Kenneth King)

There are six common types of simple machines, including the lever, the inclined plane, the wheel and axle, the screw, the wedge, and the pulley. In each case, they serve to trade off the size of the force applied for a change in the direction, distance, or speed of the applied force. In all cases, the work input to the system remains constant: WINPUT = WOUTPUT or FINPUTDINPUT = FOUTPUTDOUTPUT.

inclined Plane

An inclined plane allows a person to move a heavy object from one level to another, but instead of going “straight up,” it allows the user to move it up a longer distance along the path of the inclined plane by using a smaller force, as represented in Figure 8.4. As with all other forces, the work needed to move the object to the top of the incline is the same, whether it moves up the ramp or is moved vertically to the same point.

Figure 8.4 Inclined Plane (drawing by Kenneth King)

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tHe wedge

The wedge functions like two back-to-back inclined planes. It allows a force to be concentrated in a small area. This is the same principle that explains the function of a knife. In fact, the sharper the blade, the smaller the area of the applied force— so a larger force can be applied in a smaller area. Figure 8.5 illustrates this idea.

Figure 8.5 Wedge (drawing by Kenneth King)

wHeel and axle

The wheel and axle provides a mechanical advantage due to the relationship between the wheel which allows the force to be moved across a large distance, and the axle, which concentrates the force in a small area. For example, a door knob allows one to move the axle that penetrates the door which in turn operates the bolt that secures the door shut. The larger door knob allows much more force to be applied to the bolt than if the bolt were operated directly, as demonstrated in Figure 8.6.

Figure 8.6 Wheel and Axle (drawing by Kenneth King)

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tHe screw

The screw operates much like an inclined plan wrapped around an axis. The convenience of the screw is that by wrapping it around a single axis, it uses a much smaller cross-sectional area than would a similar inclined plane. Figure 8.6 shows the relationship between a screw and an inclined plane.

Figure 8.7 Screw (drawing by Kenneth King)

PUlley

A pulley, as with other simple machines, offers the ability to apply a smaller force over a longer distance, allowing forces to be concentrated when accomplishing work. By adding additional pulleys to a pulley system, the effort required to move an object becomes smaller and smaller.

Figure 8.8 Pulley (drawing by Kenneth King)

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Torque is the equivalent of force for circular motion. As a force can be thought of as a push or a pull, a torque can be considered a twist. One way to appreciate the nature of a torque is to consider using a wrench on a bolt. The twisting force applied to the bolt can be increased by applying the force farther out on the handle of the wrench. By increasing the distance between the point where the bolt rotates and the point where the force is applied to the wrench, the twisting force or the torque can be increased.

Figure 8.9 Torque (drawing by Kenneth King)

Torques can be helpful when considering the nature of forces that operate on simple machines. A see-saw is a simple example of a lever in action. Two children of different weights, balanced on the see-saw at different distances from the pivot point, can produce torques that are equal in size and opposite in direction, so there is a net torque of zero. We can see this directly because the sea-saw is in balance.

Figure 8.10 See-Saw (drawing by Kenneth King)

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conservation of energy and MoMentUM energy

The bowling ball described in the previous section was said to have kinetic energy when it was in motion and potential energy when it was teetering on the edge of a windowsill. The Law of Conservation of Energy is an important concept for understanding the movement of energy. Simply stated, it is known that energy can never be created or destroyed, but it can be transferred from object to object and from one form of energy to another form of energy. In the bowling ball example, the Law of Conservation of Energy makes it possible to describe the behavior of the bowling ball and the energy associated with it. The work it took to raise the bowling ball to the window ledge required energy. The potential energy gained by the bowling ball is equivalent in quantity to the work needed to raise it to the windowsill. When the ball falls from the window ledge, it gains kinetic energy as it falls toward the ground. During its fall to the ground, the total energy available to the bowling ball remains constant because the sum of the potential and kinetic energy remains the same. This result is an example of the law of the conservation of energy. Simply stated, it requires that the total energy available is the sum of the kinetic energy and potential energy and this quantity of energy remains constant. This idea is represented graphically in Figure 8.11

Figure 8.11 Kinetic and Potential Energy (drawing by Kenneth King)

MoMentUM

You know intuitively that a car coasting down a gentle hill is harder to stop than a skateboard coasting down the same hill at the same speed. This is due to the car having a greater momentum than the skateboard. Momentum is the combination of the mass of a body and its velocity. We express it as an equation as in this manner: momentum = (mass) X (velocity), or p = mv. The relationship, between the momentum and its mass and velocity is directly proportional; therefore, doubling either the mass of an object or the speed of an object doubles the object’s momentum.

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Momentum is conserved because the total momentum in a system remains constant. Momentum can also be transferred from one object to another object. Playing a game of billiards demonstrates this concept very simply. A moving cue ball collides with a second ball on the table, setting the second ball into motion. The first ball transferred some or all of its momentum to the second ball. A desktop toy called a Newton’s Cradle shows this as well, as represented in Figure 8.12.

Figure 8.12 Momentum (drawing by Kenneth King)

gravitation All objects experience the force of gravitation. Gravitation is the attractive force between two objects. Gravity is the force between the earth and a body being pulled towards the earth. You are likely aware of the story of an apple said to have fallen on Sir Isaac Newton’s head. The real point of the story is not being struck by an apple but the insight that Newton achieved as he watched the apple fall to the earth. He recognized for the first time the concept of a force at a distance; the force that caused the apple to fall to the Earth is the same force that causes the moon to fall toward the Earth. As mentioned above, all objects exert a gravitational force upon all other objects. The size of the gravitational force depends on two sets of circumstances: the mass of each of the objects and the distance between the objects. Increasing the distance between the objects causes the size of the attractive force between them to grow smaller. For a person standing on the surface of the Earth, this force is perceived as weight. If the same person were to climb to the top of a very tall mountain and measure his or her weight using a very sensitive scale, he or she would measure a decrease in the amount of weight, but the amount of substance that they are made from (their mass) remains the same. This change in the size of the force is caused by moving the objects farther apart from one another. The size of the objects, their mass, also influences the size of the gravitational force. Simply put, the larger the masses, the larger the force. The distance from the sun to the earth and the sun to the moon is essentially the same, about 150 million kilometers. The size of the force between the sun and the earth is much larger than the size of the force between the moon and the sun because the earth’s mass is much larger than the moon’s mass.

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arcHiMedes’ PrinciPle In the third century BC, the Greek scientist Archimedes recognized the relationship between buoyancy and the liquid displaced by an object placed in a vessel of liquid. Archimedes’ Principle states, “an immersed body of liquid is buoyed up by a force equal to the weight of the fluid it displaces” (Hewitt, Suchocki, and Hewitt 2004, 139). Stated more succinctly, buoyancy is equal to the weight of the displaced liquid. If an immersed body displaces one kilogram of liquid, the buoyant force supporting the body produces an opposing force equivalent to the force acting on a mass of one kilogram. One consequence of Archimede’s principle is that it is easier to lift submerged bodies. It reduces the apparent weight of underwater bodies while the object is submerged.

BernoUlli’s PrinciPle Bernolulli’s principle, proposed by Swiss scientist Daniel Bernoulli in the eighteenth century can be stated as follows: “When the speed of a liquid increases, the internal pressure in the fluid decreases” (Hewitt, Suchocki, and Hewitt 2004, 151). A consequence of Bernoulli’s principle is the force of lift on an airplane wing. The air moves faster over the top surface of the wing because it has a greater distance to travel then the air moving along the bottom part of the wing. This causes a decrease in pressure over the wing, with respect to the overall atmospheric pressure experienced beneath the wing. The smaller pressure on the top surface of the wing produces a net push in the upward direction. As a result, the wing, with the plane attached, rises.

general tHeory of relativity The equations used to describe the force of gravitation since the time of Newton are still used today and provide an excellent means of describing movement of stars, planets, and of objects orbiting the earth. The work of Albert Einstein during the early decades of the twentieth century, however, demonstrated that Newton’s description of gravitation is a small part of a broader understanding of motion. These more broadly constructed descriptions are referred to as parts of the General Theory of Relativity. The basic idea of the General Theory of Relativity is that it is impossible for an observer to distinguish between an accelerated frame of reference (such as inside a space capsule, speeding up as it moves away from the earth) and the same sensation produced by a gravitational field. Einstein used this idea, that acceleration and gravitation are indistinguishable from one another, as the foundation for his model of the universe.

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A ball tossed from one person to another in either a gravitational field or in an accelerating spacecraft would follow the arc described in the section on Projectile Motion above. From the perspective of the general theory of relativity, the arc they follow is due to the warping or bending of space itself. The path that objects follow is due to the warping and bending of space in the presence of mass. This bending of space itself, and the curved path an object follows through space is what we perceive as the force of gravitation. The greater the mass, the greater the bending, and the greater the force we perceive. While we are not accustomed to thinking of space in this manner, the model of a large rubber sheet is sometimes helpful. Placing a bowling ball on the large rubber sheet causes a depression in the sheet. Rolling a marble past the bowling ball causes it to have its path deflected by the depression in the sheet. This is the model that Einstein developed. In the explanation developed by Newton, we consider not a bending of space, but the idea of a force acting on an object and causing its path to be deflected. This example illustrates that Newton’s explanation is a special case of the more general explanation put forward by Einstein.

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review QUestions—cHaPter 8 1. What is true of a ball rolling across a smooth, level surface? a. The ball will keep moving in a straight line at a constant speed, unless an outside force actions on it. b. In the “real world,” the force of friction will eventually cause a rolling ball to come to a stop. c. Both a and b. d. None of the above. 2. Playing “catch” with a softball would best be described as an example of which form of motion? a. Projectile motion. b. Uniform linear motion. c. Circular motion. d. Periodic motion. 3. Swinging a yo-yo at the end of a string in circles around your head would be a good example of what type of motion? a. Projectile motion. b. Uniform linear motion. c. Circular motion. d. Periodic motion. 4. An ice skater gliding across a smooth, frozen surface best shows which of the following types of motion? a. Projectile motion. b. Uniform linear motion. c. Circular motion. d. Periodic motion. 5. A spring with a weight on it, gently bouncing up and down, is an example of which of the following types of motion? a. Projectile motion. b. Uniform linear motion. c. Circular motion. d. Periodic motion.

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6. Causing a coasting car to stop by applying a force to it would provide an application of which of Newton’s Three Laws of Motion? a. First Law of Motion. b. Second Law of Motion. c. Third Law of Motion. d. None of the above. 7. Jumping off of a boat into a body of water—and pushing the boat backwards at the same time—is a good example of which of Newton’s Laws of Motion? a. First Law of Motion. b. Second Law of Motion. c. Third Law of Motion. d. None of the above. 8. Applying a force to a body and causing it to move faster is an example of which of Newton’s Three Laws of Motion? a. First Law of Motion. b. Second Law of Motion. c. Third Law of Motion. d. None of the above. 9. Pushing against a wall does not accomplish work in the scientific sense because a. no force is applied. b. there is no displacement. c. work can only be calculated through vertical movement. d. none of the above. 10. The consequences of the Law of Conservation of Energy are that a. energy can neither be created nor destroyed. b. energy can be transferred from one object to another. c. in a closed system, the sum of the kinetic and potential energy remain constant. d. all of the above. 11. Power is described as the rate that work is accomplished. Which of the following examples generates the greatest power? a. A 75 kg runner in a race travelling 60 meters in 40 seconds. b. A 75 kg runner in a race travelling 60 meters in 30 seconds. c. A 75 kg runner in a race travelling 60 meters in 20 seconds. d. All of the above are the same, since the distance does not change.

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12. An inclined plane is shown in Figure 8.13 below. Which statement is most true?

Figure 8.13 Inclined Plane (drawing by Kenneth King)

a. Moving the mass straight up 3 meters will require the most work, because it is a direct vertical displacement. b. Moving the mass 5 meters along the inclined plane will require the most work, because of the longer distance it moves. c. The work done is the same in either case. d. There is not enough information to answer this question. 13. Torque is described as a rotational force. Imagine two children sitting on a see-saw and in balance. One of the children moves closer to the pivot point; the other remains in place. Which of the following best describes what happens next? a. The torques are no longer equal and opposite, so the see-saw moves downwards, from the point of view of the child who did not move. The child who did not move has the greater net torque. b. The torques are no longer equal and opposite, so the see-saw moves upwards, from the point of view of the child who did not move. The child who did not move has the smaller net torque. c. Because the net torque must remain constant, even when a child moves the see-saw will not pivot. d. None of the above are correct. 14. Which of the following games offers the most evident demonstration of the properties of momentum? a. Swimming. b. Billiards. c. Playing catch. d. All of these illustrate properties of momentum equally well.

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Mechanics (Answer Key: 1.d, 2.a, 3.c, 4.b, 5.d, 6.a, 7.c, 8.b, 9.b, 10.d, 11.c, 12.c, 13.a, 14.b) Works Cited

Hewitt, Paul, John Suchocki, and Leslie A. Hewitt. Conceptual Physical Science. San Francisco, CA: Pearson Education, 2004. Print.

Chapter 9

ELECTRICITY AND MAGNETISM Craig A. Wilson

rePUlsion and attraction of electric cHarges Electrically charged objects may either repulse or attract other objects. If two objects have like charges, they will repel each other. For example, if you rub two balloons against a piece of wool cloth, they will pick up excess electrons from the cloth and so become negatively charged. When you bring the balloons together, they will repel each other because they have the same type of charge. When two objects have unlike charges, they attract each other. If you were to take a charged balloon and hold it next to a wall, the excess electrons in the balloon would push away some of the electrons in the wall, giving the area of the wall closest to the balloon a positive charge. Thus the balloon and the wall would be attracted to each other, due to the fact that the balloon has a negative charge and the wall has positive charge.

series and Parallel circUits One way that bulbs and dry cells may be connected is in series circuits. They are called series circuits because there is only one pathway and the electricity flows through each part of the circuit in series. This is why all the bulbs go out when you remove one bulb or one dry cell from a series circuit. Some of the old Christmas tree lights were connected in series. This made it very difficult to locate a burned out bulb, since they would all go out at once. When bulbs are connected in series, one wire should be hooked to each side of the bulb holder (as shown in Figure 9.1). As bulbs are added to a series circuit, the

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bulbs get dimmer. The reason for this is that each bulb takes more electricity from the circuit.

Figure 9.1 Bulbs Wired in Series (drawing by Craig Wilson)

With series circuits, the negative terminals are wired to the positive terminals on the dry cell (as shown in Figure 9.2). As dry cells are added to a series circuit, the bulbs get brighter. This is because each of the dry cells adds more electricity to the circuit. So dry cells wired in series do not last as long as those wired in parallel.

Figure 9.2 Dry Cells Wired in Series (drawing by Craig Wilson)

Bulbs and dry cells may also be connected in parallel circuits. They are called parallel circuits because there are two pathways running side by side or parallel to each other. This is why you can remove one bulb or one dry cell from a parallel circuit without affecting the remaining bulbs. Today most Christmas tree lights are wired in parallel. Because of this, the bulbs stay lit, even if one goes out. When connecting bulbs in parallel, two wires are attached to each side of the bulb holder (as shown in Figure 9.3). As bulbs are added to a parallel circuit, the other bulbs do not get dimmer. This is because each bulb has its own pathway. Since there is more than one pathway in a parallel circuit, it is possible to remove a dry cell or a bulb and not affect the rest of the circuit.

Figure 9.3 Bulbs Wired in Parallel (drawing by Craig Wilson)

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With parallel circuits, the positive terminals are wired to the positive terminals and the negative terminals are wired to the negative terminals on the dry cell (as shown in Figure 9.4). As dry cells are added to a parallel circuit, the bulbs do not get brighter because electricity flows from only one dry cell at a time. Because of this, dry cells wired in parallel last longer than those in series.

Figure 9.4 Dry Cells Wired in Parallel (drawing by Craig Wilson)

condUctors and insUlators Conductors are materials that allow electrons to move freely through them. Metals such as copper and aluminum make the best conductors, although carbon and water containing compounds such as NaCl will also conduct electricity. Conversely, electrons do not move through insulators easily. Insulators include nonmetals such as plastic, rubber and glass.

oHM’s law Ohm’s Law is named after a German scientist named George S. Ohm who discovered the relationship among resistance, voltage, and current. Ohm’s Law is illustrated in the following formulas: R = V/I

I = V/R

V=RxI

The R stands for resistance (measured in ohms), the V stands for voltage (measured in volts)and the I stands for amount of current that is flowing (measured in amps). If you know any two of the three amounts, you can use one of the formulas above to calculate the third. Note from the first formula that, as resistance goes up, the amount of voltage also must go up and/or the amount of current must go down. See if you can figure out similar relationships, based on the second and third formulas.

direct cUrrent and alternating cUrrent flow Direct current moves electrical charges in one direction. The current produced by dry cells moves only in one direction, so this is an example of direct current.

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Alternating current moves back and forth several times each second, so there is no overall change in the position of the electrical charge. Electrical generators, such as those found in electric power stations, produce alternating current.

soUrces of eMf The three major sources of Electromotive Force (EMF) include storage cells, photo cells, and generators. Storage cells work by converting chemical energy into electrical energy. With primary storage cells (e.g., a flashlight cell) the chemical reactions are irreversible and so the chemical energy can only be used once. In secondary storage cells (e.g., a car battery), the chemical reactions are reversible; during charging, electrical energy is stored as chemical energy, while during discharging chemical energy is converted into electrical energy. Photocells are made of photoelectric metals such as potassium (K) and sodium (Na). When photoelectric metals are struck by light, they emit electrons, thus producing electricity. As the intensity of the light increases, the amount of electrical energy produced by the photocell increases. A generator converts mechanical energy into electrical energy. Generators consist of three major parts—a magnet, a coil of wire, and an iron core. The iron core is connected to an engine or a turbine, which causes it to rotate. As the coil of wire that is wrapped around the iron core moves through the magnetic field, an electric current is induced and the current is carried away by wires that are connected to the coil.

Magnetic fields and Magnetic forces If you were to place several compasses around a bar magnet, you would notice that the needles all point toward the poles of the magnet. The reason for this is that all magnets have a magnetic field and the magnetic forces are stronger at the north

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and south poles of a magnet. If you were to sprinkle iron filings onto a bar magnet, more iron filings would be attracted to the poles of the magnet than to the center of the magnet. Scientists have discovered that this magnetic field occurs when groups of atoms in a magnet (called magnetic domains) line up in a north-south direction. As a result, the north pole of each atom points in one direction while the south pole of each atom points in the opposite direction (as shown in Figure 9.6) N

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Permanent magnets keep their magnetism as long as the domains stay lined up, which can be for several years. It is possible to make a permanent magnet out of certain objects such as a sewing needle, simply by stroking the object in one direction for about 30 seconds on one pole of a bar magnet. When you do this, the magnetic domains in the needle line up in a north-south direction. Substances such as plastic, wood, and glass do not contain magnetic domains, and so cannot be magnetized. It is also possible to magnetize certain objects by using an electrical current (as shown in Figure 9.7). The electricity flowing through the coil of wire causes the magnetic domains in the iron nail to line up and the nail becomes an “electromagnet.” As soon as the current is shut off, however, the

Figure 9.7 Electromagnet (Drawing by Lindsay Gaughan)

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nail loses its magnetism and so it is described as a “temporary magnet.” It would be possible to increase the strength of this electromagnet by wrapping more coil of wire around it or by using a more powerful battery. It is important to note that magnetism will pass through materials such as paper and plastic, but it will not pass through materials such as steel and iron. If you were to pass a piece of paper between a suspended paperclip and a magnet (as shown in Figure 9.8), there would be no effect on the paperclip, but it you were to pass a steel plate between them, the paperclip would fall. In scientific terms we would say that paper and plastic are “transparent” to magnetism and steel and iron are “opaque.”

Figure 9.8 Magnetic Transparency (Drawing by Lindsay Gaughan)

transforMers and Motors The purpose of a transformer is to either increase or decrease the voltage in a circuit with alternating current. There are three parts to a transformer—the primary coil, secondary coil, and the iron core (as shown in Figure 9.9). As the alternating current comes into the primary coil, it produces a magnetic field in the iron core. This magnetic field then induces voltage in the secondary coil. If there are more coils in the secondary coil then in the primary coil, the voltage produced will be greater than the voltage coming in. This is called a “step-up” transformer. If there are more coils in the primary coil then in the secondary coil, the voltage produced will be less than the voltage coming in and so this is called a “step-down” transformer.

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Primary winding

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Figure 9.9 Transformer (Drawing by Andrew Cross)

Electric motors consist of four major components—an armature, a pair of field magnets, a pair of brushes, and a split ring commutator (as shown in Figure 9.10). The armature is an electromagnet that revolves between the two field magnets. The north pole of one field magnet is placed near one end of the armature, while the south pole of the other field magnet is placed near the opposite end of the armature.

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The two brushes are placed on the two sides of the split-ring commutator and their purpose is to conduct electric current from the power source to the armature. The two halves of the split-ring commutator are attached to the armature. As the armature rotates, the split-ring commutator causes the direction of the current in the armature to reverse. As the current in the armature reverses, the magnetic field of the armature also reverses, causing it to revolve between the two field magnets.

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review QUestions—cHaPter 9 1. If you were to bring two electrically charged objects close together and they repelled each other, it is likely that which of the following is true? a. Both objects are negatively charged. b. Both objects are positively charged. c. Both a and b are possible. d. Neither a nor b is possible. 2. Electromotive force is a measure of which of the following? a. The rate at which current flows through a circuit. b. The number of electrical appliances that are included in a circuit. c. The amount of resistance in an circuit. d. The pressure that pushes the current through a circuit. 3. If two bulbs are wired in a parallel, what would happen to one bulb it you removed the other bulb. a. It would go out because is one pathway. b. It would stay lit because there is one pathway. c. It would go out because there are two pathways. d. It would stay lit because there are two pathways. 4. One of the major differences among conductors and insulators is that a. electrons move more freely through conductors. b. insulators can be solids or liquid, whereas conductors are always solids. c. insulators are generally made of denser materials. d. conductors are usually made out of nonmetal materials. . 5. A light bulb with a resistance of 2 ohms is connected to a 110 volt circuit. Using Ohm’s Law, how much current would flow through the bulb? a. 220 amperes. b. 112 amperes. c. 2 amperes. d. 55 amperes. 6. Direct current is to dry cell as ____________ is to electric power station. a. alternating current b. indirect current c. high voltage current d. solid state current

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7. Which of the following sources of electromotive force (EMF) produces energy through chemical reactions? a. Storage cells. b. Photocells. c. Generators. d. All of the above. 8. A paper clip is fastened to a string and suspended in mid-air by a magnet. A square sheet of paper is placed in the space between the magnet and the paper clip. Predict what will happen to the paper clip. a. It will not move because paper is opaque to magnetism. b. It will not move because paper does not have a noticeable impact on magnetic fields. c. It will drop because the paper disrupts the magnetic lines of force. d. It will move to the side slightly because the paper becomes a temporary magnet. 9. Which of the following is true in a step-up transformer? a. The number of coils in the primary coil is equal to the number of coils in the secondary coil. b. The number of coils in the primary coil is greater than the number of coils in the secondary coil. c. The number of coils in the secondary coil is greater than the number of coils in the primary coil. d. The secondary coil will always have 10 coils. (Answer Key: 1.a, 2.d, 3.d, 4.a, 5,d, 6.b, 7.a, 8.b, 9.c)

Chapter 10

WAVE PHENOMENON Anton Puvirajah

Waves are disturbances that move from one place to another and in the process transfer energy. For example, a rock dropped into a pond creates waves as the (gravitational) energy of the dropping rock is transferred to the water. When this happens, disturbance in the water occurs as the energy is transferred radially from the point of impact of the rock (as shown in Figure 10.1). Sound and light energy also travel in waves. Sound from a strummed guitar travels as sound waves radially through the air in all directions. If we happen to be in the path of this, our ears will recognize the waves as sound. In this case, energy produced by the strumming of the guitar is transferred through the air. Certain properties of light can also be explained by waves. Light from the sun travels in all directions in form of waves. The Earth being in its path receives some of this light, as do other planets in our solar system.

Figure 10.1 Disturbance in the water occurs as the energy is transferred radially from the point of impact of the rock. (Drawing by Elizabeth Throop)

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transverse and longitUdinal waves There are two fundamental types of waves--transverse and longitudinal waves. Transverse waves can be observed by tying one end of a string to a doorknob, then holding the other end relatively taut and moving this end up and down (as shown in Figure 10.2). In transverse waves the transfer of energy, that is the movement or the propagation of the wave, is at right angles (perpendicular) to the movement of the vibration (as shown in Figure 10.2). In the string example above, the wave propagates from the handheld end to the doorknob as the string is moved up and down. The movement of the hand up and down is at right angle to the movement of the wave. Doing the wave at a baseball game can be used as an analogy for a transverse wave. The wave propagates around the stadium, but the people move up and down at right angles (perpendicular) to the wave. Examples of transverse waves include electromagnetic waves (visible light, x-rays and radio waves) and some types of seismic waves (s-waves).

Figure 10.2 Transverse wave propagation is at right angle to the movement. (Drawing by Elizabeth Throop)

Longitudinal waves can be observed by laying a helical spring or a Slinky on the floor, anchoring one end, and then pulling out and pushing in (pumping action) the other end. The pulling stretches the spring and the pushing compresses the spring (as shown in Figure 10.3). In longitudinal waves the transfer of energy, that is the movement or the propagation of the wave, is parallel to the movement of the vibration. In the spring example, the initial stretch and the compression of the spring propagate down the spring toward the other end as the spring is pulled out and pushed in. Thus in longitudinal waves, energy is transferred through compression and spreading apart (rarefaction) of particles. Examples of longitudinal waves include sound waves travelling through air, oscillations in springs, and some types of seismic waves (p-waves).

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Figure 10.3 Longitudinal waves in a spring showing compressions and rarefactions. (Drawing by Elizabeth Throop)

wavelengtH, aMPlitUde, freQUency, sPeed Wavelength is the length of one cycle of the wave and is measured from one point on a wave to the corresponding point on the next wave cycle. A simple way to determine the wavelength of a transverse wave is to measure from the crest of one wave to the crest of the adjacent wave or from the trough of one wave to the trough of the adjacent wave (as shown in Figure 10.4).

Figure 10.4 Parts of a transverse wave. (Drawing by Elizabeth Throop)

The crest of a wave is the highest point on the wave and the trough of a wave is the lowest point on the wave. Wavelength of a longitudinal wave is determined by measuring from one compression point to the next compression point or from one rarefaction point to the next rarefaction point (as shown in Figure 10.5). A compression point of a longitudinal wave is the point at which there is maximum density of particles or where the distance separating the particles is the least. A rarefaction point of a longitudinal wave is the point at which there is minimum density of particles or where the distance separating the particles is the most.

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Figure 10.5 Low and high amplitude longitudinal waves. (Drawing by Elizabeth Throop)

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Amplitude of a wave is the measure of the shift from the undisturbed or equilibrium position to the maximum displacement position. Amplitude of the wave is indicative of the energy the wave possesses. Greater the energy put into creating a wave, the greater the resulting amplitude. For a transverse wave, the amplitude is either the height or the depth of the wave from its equilibrium position. Thus, amplitude is the distance measured from the equilibrium position to either the crest or the trough of the wave (as shown in Figure 10.4). For a longitudinal wave, the amplitude is the measure of the magnitude of compression or rarefaction from the equilibrium position. The greater the energy put into creating a compression wave, the greater the resulting magnitude of the compression from the equilibrium position (as shown in Figure 10.5). The frequency of a wave is the measure of how many waves pass through in a given point in time. Frequency is often expressed as the number of (waves) cycles per second. For example, standing at the water’s edge, we can determine the frequency of an ocean wave at the beach by counting the number of times a wave hits our ankles in a given length of time. So if 100 waves hit our ankles in 40 seconds, the frequency of the wave is 100 waves per 40 seconds (100 waves/40 sec) or 2.5 waves per one second (2.5 waves/sec). The unit time used in frequency is often one second. The scientific unit (SI unit) for frequency is the Hertz (Hz). Thus one Hz is equal to one cycle per second. So the scientific expression for the frequency of water waves hitting the ankles from the above scenario is then 2.5 Hz. Very much related to the frequency of a wave is the period of a wave. The period of a wave is the time required for one complete wave cycle to pass a given point. Thus, the period of a wave can be determined from the frequency of the wave (as shown in Figure 10.6). For example,

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let’s say we know that 2.5 (2.5 Hz) waves pass in one second. Then to calculate how many seconds it takes to for one wave to pass through (the period), we can do the following: 2.5 waves 1 wave = 1 second x

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The frequency of the wave is 2 waves per second or 2 Hz. A simple relationship between frequency and period may have been realized by working out the above problems. Frequency is the reciprocal of period and vice versa. Thus: Frequency =

1 1 and Period = Period Frequency

The speed of waves varies depending of the type of wave and the media through which it travels. For example, during a thunderstorm both lightening and thunder occur at the same time. However, we see the lightening first and then hear the thunder later. This is because light waves travel faster than sound waves. The speed of waves, much like speed of cars, is the measure of how far a wave travels in given span of time. Normally, the distance traveled by a wave in one second is used for determining the speed of the wave. If an ocean wave travels 500 meters

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Figure 10.6 Frequency and period of a wave. (Drawing by Elizabeth Throop)

in 90 seconds, the speed of the wave is 500 meters/90 seconds or 5.6 meters/ second. The speed of a wave is related to its wavelength, frequency, and period. Thus: Speed =

Distance Wavelength , Speed = Wavelength x Frequency, Speed = Time Period

reflection, diffUsion, refraction, aBsorPtion, transMission When a moving wave encounters a different medium than the one through which it is traveling, the wave becomes reflected, refracted, diffused, absorbed, or transmitted. Reflection occurs when a traveling wave encounters some form of barrier and is turned back from the barrier (as shown in Figure 10.7).

Figure 10.7 A wave being reflected as it encounters a barrier. (Drawing by Elizabeth Throop)

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Depending of the surface (barrier) that is encountered, there may not be a complete reflection of the wave. Some of the energy of the wave may get absorbed or passed through the barrier instead of being reflected. Sunglasses that allow us to see the wearer’s eyes while at the same time allowing us to see a reflection of ourselves are an example of this. A wave that moves toward a barrier to strike it is called the incident wave. The wave that reflects back is called the reflected wave. Waves that reflect off of barriers follow a certain pattern or law. The law of reflection states that reflected angle of the wave will be the same as the incident angle of the wave (as shown in Figures 10.7 and 10.8). Echoing of sound, light bouncing off a mirror, and ripples in a pool bouncing off of the side walls are all examples of waves reflecting.

Figure 10.8 An incident wave and reflected wave have the same angle to the normal. (Drawing by Elizabeth Throop)

When a wave encounters a reflecting barrier that is smooth and shiny (like a mirror) all parts of the reflected wave will have the same angle. This is because there is one only one incident angle and thus one reflected angle (as shown in Figure 10.8). On a mirror this produces a reflection that is similar to the incident wave. However when a wave encounters a reflecting barrier that is rough and dull (like a piece of rock), parts of the wave get reflected back at different angles. This is because the rough surface produces a multitude of incident angles and thus the resulting reflection also has a multitude of reflected angles (as shown in Figure 10.9). This phenomenon is called diffuse reflection. A still lake produces regular reflection where we’re able to see ourselves in it. A choppy lake produces diffuse reflection where we cannot see ourselves clearly.

Figure 10.9 A jagged surface also follows the law of reflection; the reflection is diffuse. (Drawing by Elizabeth Throop)

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A wave’s speed changes as it passes form one medium to another. For example, when light passes from air to water, its speed is slowed. The reason is that the density of the medium through which the wave travels affects the speed of the wave. Waves will travel slower in higher density media and faster in lower density media. For example, light will travel fastest in empty space, a little slower in air, and even slower water. Refraction, a phenomenon in which a wave bends or changes direction, occurs when a wave encounters a medium at an angle, resulting in parts of the wave entering the medium earlier than other parts. So at that instant, parts of the wave (in the original medium) travel at the original speed and other parts of the wave (in the new medium) travel at the new changed speed (as shown in Figure 10.10). This causes the wave to bend. Waves going from a faster medium to a slower medium bend toward the normal and waves going from a slower medium to a faster medium bend away from the normal. A classic example of refraction is illustrated in Figure 10.11, where the straw looks broken in a glass of water.

Figure 10.10 Refraction – A wave moving from a faster medium to a slower medium will bend toward the normal. (Drawing by Elizabeth Throop)

Figure 10.11 Refraction of a straw in a glass of water. (Drawing by Elizabeth Throop)

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A traveling wave encountering certain types of media can become absorbed by or transmitted through the media. That is, when energy travelling in form of waves strikes certain types of matter, the energy is either transferred to the matter (absorbed) or it passes through the matter (transmitted). Sometimes a combination of the two occurs. For example, light waves from the sun are absorbed by a black colored roof. However, the light waves are transmitted through a clear glass skylight. Black colored objects absorb, white colored objects reflect, and clear objects transmit visible light.

diffraction and interference When a traveling wave encounters an object, the wave can move or bend around the object, then change direction, and continue its travel along areas behind the object. This phenomenon is called diffraction. We are able to hear sounds coming from a different room because sound waves are able to go around the edges of the opening, change direction, and travel to the next room (as shown in Figure 10.12). Diffraction of waves around objects depends on the relative sizes of the object to the wavelength. Diffraction is more pronounced when the wavelength is larger than the object and less pronounced when the wavelength is smaller than the object. We are able to receive cellphone signals around most tall buildings and corners of rooms because of the ability of cellphone radio waves to bend around buildings, doorways, and most other obstacles.

Figure 10.12 Diffraction – Sound from one room is heard in the next room as it travels around the wall. (Drawing by Elizabeth Throop)

A phenomenon called interference occurs when two waves traveling toward each other along the same medium meet and overlap to form a new wave. Depending on how the waves overlap, the interference can either be constructive or destructive. Constructive interference occurs when two waves in the same phase overlap to yield a new combined wave with higher wave energy. Being in the same phase means that both overlapping waves are either above the rest (the normal) position or below the rest position.

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When parts of the two waves which are either both above or below the normal meet, the result is larger amplitude (as shown in Figure 10.13). This is because the two crests or the two troughs of the waves add together. For example, say that two crests, one with amplitude +1 and the other with amplitude +2 meet. The combined wave will have an amplitude of +3 because (+1) + (+2) = +3. Similarly, if two troughs, one with amplitude -1.5 and the other with amplitude -1.0 meet, then the combined wave will have an amplitude of -2.5 because (-1.5) + (-1.0) = -2.5. In essence, the amplitudes are additive in constructive interference. Knowing constructive interference, it may be possible to understand processes involved in destructive interference.

Figure 10.13 Constructive interference of two waves in phase. (Drawing by Elizabeth Throop)

Destructive interference occurs when two waves in opposite phases overlap to yield a new combined wave with lower wave energy. In opposite phases, one of the overlapping waves will be above the rest position and the other overlapping wave will be below the rest position. When these opposite phase waves meet, the result is smaller amplitude (as shown Figure 10.14). This is because the crest of one wave and the trough of the other wave add together. Let’s say that a crest with an amplitude of +1 meets a trough with an amplitude of -1. The combined wave will have an amplitude of zero because (+1) + (-1) = 0. Similarly if crest with an amplitude of +2 meets with a trough having an amplitude of -3, then the combined wave will have an amplitude of -1 because (+2) + (-3) = -1. In essence, the amplitudes are subtractive in destructive interference.

Figure 10.14 Destructive interference of two waves in out of phase. (Drawing by Elizabeth Throop)

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doPPler effect The Doppler Effect is a phenomenon created by a moving source that generates waves. When a source creates waves as it moves, individuals located on the path of the waves appear to experience (e.g. hear, see) constantly changing frequency/ wavelength of the waves. Individuals, who have the source coming closer to them, experience progressively increasing frequency and shortening wavelength. Individuals who have the source moving away from them experience progressively decreasing frequency and increasing wavelength (as shown in Figure 10.15). The Doppler effect is experienced because of the movement of the source of the wave from one point to the next creating an apparent shift in time/distance it takes for the wave to reach the observer. For example, a person standing on the sidewalk can hear the frequency (pitch) of an emergency vehicle’s siren increase as the vehicle approaches him and hear the frequency decrease as the vehicle goes past him. This is because, as the vehicle approaches, the time it takes for the wave to reach the person decreases and the as the vehicle moves away, the time it takes for the wave to reach the person increases. Another example of the Doppler effect is the horn sound of a train approaching and then going past you.

Figure 10.15 Doppler effect is created as the moving vehicle generates sound waves. (Drawing by Elizabeth Throop)

cHaracteristics of soUnd waves Some waves like sound waves are called mechanical waves because they require a material media or media made of matter to travel. Sound waves are also classified as longitudinal or compression waves because the propagation of sound energy is parallel to the vibration of the media and causes the compression and rarefication the air as it travels. We primarily hear sound as it travels through the air to our ear. Sound also travels through particles of solid and liquids. Sound however cannot travel in a vacuum, as there are no particles of matter in a vacuum to carry the sound wave. The vibration of matter creates sound. The energy of vibration travels through the air to our eardrums by means of compression and rarefication of air. Because

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vibration produces sound, when we want to muffle or quiet a sound we try to reduce the vibration. When we reduce or stop the vibration, the sound is also reduced or stopped. For example, sound from the clash of cymbals is stopped or muffled as the player pinches the cymbals with her fingers. We produce sound by passing air from our lungs over our vocal cords and out our mouths. The vocal cords vibrate and in turn the air surrounding the vocal cords also vibrate to produce sound as air from the lungs pass over the vocal cords. Sound is further manipulated as it travels out the mouth. Different sounds travel at the same speed in a given media. For example, sound of a dog barking, ice-cream truck passing-by, lawn mower, and children playing all travel at the same speed through the air. However, the speed of sound depends on the type and condition of the medium. Sound travels slower in cold air than in warm air. For example, at an air temperature of 20°C sound travels 343 meters/second and at 0°C sound travels 331 meter/second. Generally the speed of sound is influenced by the temperature, density, and elasticity of the medium through which it travels. These three factors describe the nature of particles that make up the medium. For a specific medium, sound travels slower at lower temperatures than higher temperatures. This is because the inherent motion of particles in a medium is slower at lower temperatures and thus the particles “pass-on” the sound energy slower. For a given state (solid, liquid, or gas) or for materials with similar properties, sound travels slower through more dense materials than less dense materials. For example, of the three metals, sound travels fastest in iron (5130 m/s, 7.87 g/cm3), then copper (3901 m/s, 8.96 g/cm3), and slowest in lead (1158 m/s, 11.34 g/cm3). This is because particles in more dense (packed more tightly) materials have difficulty moving quickly and transferring sound energy. Elasticity, the tendency of particles in a material to move back to its original position after being displaced, affects how sound travels. Sound travels faster in a medium that is more elastic than in a medium that is less elastic. In general, solids are more elastic than liquids or gases. This is because, particles of solids do not get displaced far, and they come back to their original position quickly. This allows for compressions and rarefactions to occur relatively quickly. Loudness is a subjective quality of the strength of sound perceived by the human ear. Loudness depends on the energy or intensity of the sound and the distance from the sound source. For example if we wanted to hear a certain song louder, we could either increase the energy of the sound by turning up the volume, or move closer to the source of the sound, or do a combination of the two. The more energy that is used to make a sound (turning up the volume), the larger the amplitude and loudness. Because sound waves travel radially outward in all directions from the origin of the sound, as the waves go further from the origin, the amount of space covered by the waves increases. However the energy of the wave remains the same. For example, with everything else being constant and ideal, the energy of a wave at a one-meter distance from the origin is the same the energy of the same wave at

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eight meters from the origin. But the wave eight meters from the origin covers a larger space (area) for the same amount of energy. Thus the energy of the sound wave per unit area is lower, further away from the origin than closer to the origin. In other words, sound gets louder as we get closer to the origin, and the loudness decreases as we move away from the origin. Intensity is a measure of the amount of energy a sound wave carries in one second through a given area. Intensity and loudness of sound can be measured in decibels (dB). The intensity of sound should then be higher closer to the origin of the sound than further away from the origin. The softest sound we can hear is at zero dB. The loudest sound we can hear without pain is at about 130 dB. Normal conversation between people is about 50 dB. How humans perceive the range of frequencies in sound is called pitch. We often refer to changes in the frequency of sound as changes in pitch. For example, in singing the musical scale do, re, mi, fa, sol, la, ti, do we would hear changes in frequency or pitch. Lower frequency notes also have lower pitch and the pitch gets higher as the frequency increases. Variations in pitch can be attributed to the nature of the sound source. For example, human voice has the ability to change pitch, by manipulating the vocal cords (relaxing and tightening). The pitch of a stringed instrument or a drum can also be changed by similar means. Tightening the string or the drum skin creates higher pitch. Thicker string or drum skin produces lower pitched sound. Pitch beyond the human range of hearing is called ultrasound (for frequencies higher than normal hearing ability) and infrasound (for frequencies lower than normal hearing ability).

electroMagnetic sPectrUM Electromagnetic waves result from the emission of electromagnetic radiation. Electromagnetic radiation is a form of energy released and captured by charged particles in motion. Charged particles are surrounded by electric fields. The motion of charged particles creates magnetic fields that are perpendicular to the electric field. When charged particles move or oscillate back-and-forth changing direction/orientation, the electric and the magnetic fields also change direction. Electromagnetic waves are generated through a continuous process where a changing orientation of the electrical filed changes the orientation of the magnetic field and the changed orientation of the magnetic field changes the orientation of the electrical field (as shown in Figure 10.16). This continuous propagation of back-and-forth changes in orientation of both the electrical and magnetic fields occur outward from the oscillating charged particle. Since all matter is made of charged particles, all matter emits electromagnetic waves. Emitted electromagnetic waves from charged particles striking other particles transfer their energy. For example, when an electromagnetic wave (energy) from the sun strikes the earth, it causes it to heat up. Electromagnetic waves, such as light, do not require a material media through which to travel so they can travel

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through a vacuum. Light from the sun, for example, travels through the vacuum of space to reach the earth because it does not need a material medium in which to travel. Electromagnetic waves travel fastest in a vacuum (300,000 km/s) and slower through matter such as air, water, and glass.

Figure 10.16 Electromagnetic field generates both electrical and magnetic fields. (Drawing by Elizabeth Throop)

Electromagnetic waves have a range of frequencies and wavelengths that depend on the rate of oscillation of the charged particles. Rate of oscillations of charged particles and the resulting frequency of electromagnetic waves are directly related. High rate of oscillations, results in high frequency and vice versa. Then we should know that high rate of oscillations, also results in shorter wavelengths. With increased frequency or decreased wavelength, the amount energy carried by the electromagnetic wave increases. The range of frequencies and wavelengths found in electromagnetic waves is called the electromagnetic spectrum. As different frequencies and wavelengths of the electromagnetic spectrum interact with objects in different ways, they have different names. The electromagnetic spectrum is normally arranged in order of increasing frequencies (as shown in Figure 10.17). In order of increasing frequencies, the electromagnetic spectrum is made of the following waves: Radio waves, Microwaves, Infrared waves, Visible light, Ultraviolet waves, X-rays, and Gamma rays. All of the above classes of electromagnetic waves have human applications.

Figure 10.17 The electromagnetic spectrum in order of increasing frequencies. (Drawing by Elizabeth Throop)

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color and tHe visiBle sPectrUM One of the most familiar forms for electromagnetic waves is the visible light that we detect with our eyes. The visible light is part of a small portion of the electromagnetic spectrum. Visible light has higher frequency and shorter wavelength than infrared waves and lower frequency and longer wavelength than ultraviolet waves. Visible light is also called the visible spectrum because of the range of colors that can be seen on the visible spectrum. These colors from the lowest to highest frequencies are red, orange, yellow, green, blue, indigo, and violet. A mnemonic that we use to remember the order of the colors is ROY G BIV. White light that we see is made of all the colors of the visible spectrum. For example, white light from the sun can be separated into its component colors by a prism. A prism separates white light into its component colors by refracting the different wavelengths of the visible light by different amounts. When visible light strikes an object, several things can happen. Objects can be classified according what happens to light as it strikes an object. Transparent objects, such as clear glass and air, let most light pass through (transmit) the object. Translucent objects, such as waxed paper, and stained glass, let some light pass through and the light that is passed through is scattered. Thus the light appears blurry, fuzzy, or undefined. Opaque objects, such as wood, and brick, do not let light pass through. In fact opaque objects either reflect or absorb the light energy. One cannot see through opaque objects. The way light interacts with the object and what the object is made of determines the color of the object. The color of the object is the color of light that reaches our eyes from the object. For example, let’s say that we shine a white light (made of ROY G BIV) on to an apple in a darkened room. The white light strikes the apple and the apple absorbs all colors except for red. Red is reflected to our eyes and we see the apple as a red apple. In the same scenario, if we see a green apple, we know that except for green, all colors were absorbed. In a darkened room if we were to shine a blue light on to a red apple, the apple would still appear dark (black), as the red apple absorbs the blue light (recall that except for red all colors are absorbed by the red apple).

geoMetric oPtics—Mirrors According to the law of reflection, the angle of reflection is the same as the angle of the incidence, when measured from the normal. Plane mirrors are flat and smooth mirrors. The image in a plane mirror appears to come from behind the mirror, is the same size as the object, and is upright. Image formed in a plane mirror is called a virtual image because the rays going out from a point on the object toward the mirror do not meet. Virtual images cannot be projected on to a wall. In Figure 10.18, object “a” sends rays toward the mirror, which reflect following the law of reflection. Then for the observer, the image seems to come from behind the mirror.

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Figure 10.18 Reflection on a plane mirror produces a virtual image. (Drawing by Elizabeth Throop)

The reflecting surface of a concave mirror is curved inward (forward) like a bowl. Again following the law of reflection, parallel rays of light striking a concave mirror get reflected back toward a focal point in front of the mirror (as shown in Figure 10.19). The more curved the mirror, the closer the focal point to the mirror.

Figure 10.19 Parallel rays of light get reflected toward the focal point in front of the concave mirror. (Drawing by Elizabeth Throop)

Depending on where the object is in front of the concave mirror and relative to the focal point, the position of the image may differ (as shown in Figure 10.20). If the object is far away from the focal point, the image that is formed is in front of the mirror, smaller, and upside down. Since the image forms in front of the mirror as a result of converging rays, it is called a real image. If the object is positioned close to the mirror so that the focal point is beyond the object, the image that is formed is behind the mirror, larger, and right side up. The image is a virtual image because rays from the object do not converge.

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Figure 10.20 Images formed by the concave mirror depend on the relative position of the object to the focal point. (Drawing by Elizabeth Throop)

The reflecting surface of a convex mirror is curved outward (backward). Light striking the convex mirror gets reflected back in all directions following the shape of the mirror, and seems to come from a point (focal point) behind the mirror (as shown in Figure 10.21). The image of an object in front of a convex mirror appears smaller, right side up, and behind the mirror. The image is virtual image (as shown in Figure 10.22).

Figure 10.21 Parallel rays of light get reflected back in all directions following the shape of the convex mirror. (Drawing by Elizabeth Throop)

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Figure 10.22 Images formed by convex mirrors appear smaller, right side up, and behind the mirror. (Drawing by Elizabeth Throop)

The Law of Refraction states, that bending of light occurs as light moves from one medium to another at an angle. How light bends depends on the refraction index of the media through which light travels (as seen in Table 10.1). When light moves from lower to higher refraction index medium the light is bent toward the normal. When light moves from higher to lower refraction index medium the light is bent away from the normal. Table 10.1 Refraction index for some common substances.

Substance Air Water Ice Glass Diamond

Refraction Index (n) 1.00 1.33 1.31 1.52 2.42

So if light moves from water to air, the light will bend away from the normal in the air (as shown in Figure 10.23). Light moving from water to glass to diamond will bend toward the normal in both glass and diamond (as shown in Figure 10.23).

Figure 10.23 Refraction of light as it travels from water to air and from water to glass to diamond. (Drawing by Elizabeth Throop)

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geoMetric oPtics—lenses Lenses are curved, transparent materials used for refracting light. Some examples where lenses are found include the human and most other animal eyes, eyeglasses, telescopes, microscopes, data projectors, and cameras. Lenses can be shaped to refract light in a specific way and are classified by their curvature. Two primary shapes of lenses are convex lens and concave lens. Convex lenses are thicker in the middle and gradually get thinner toward the edges. Rays of light, parallel to the optical axis, traveling through a convex lens bend toward the focal point found behind the lens (as shown in Figure 10.24).

Figure 10.24 Converging rays of light in a convex lens. (Drawing by Elizabeth Throop)

Depending on how an object is positioned in front of a convex lens, a virtual or a real image is formed (as shown in Figure 10.25). If an object is positioned farther away from the lens than the focal point, a real image is formed on the other side of the lens. However, if an object is positioned closer to the lens than the focal point, a virtual image that is larger than the object is formed on the same side of the lens as the object.

Figure 10.25 Images formed by a convex lens depend on the relative position of the object to the focal point. (Drawing by Elizabeth Throop)

Concave lenses are thinner in the middle and progressively get thicker toward the edges. Rays of light, parallel to the optical axis, traveling through a concave lens diverge away and outward from the optical axis (as shown in Figure 9.26). Irrelevant of the position of the object in front of the concave lens, images formed are always smaller and virtual (as seen in Figure 10.27).

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Figure 10.26 Diverging rays of light in a concave lens. (Drawing by Elizabeth Throop)

Figure 10.27 Images formed by a concave lens are always smaller and virtual. (Drawing by Elizabeth Throop)

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review QUestions—cHaPter 10 1. All waves are said to disturbances that move from one place to another and in the process transfer __________. a. particles b. energy c. sound d. light 2. The type of wave in which the transfer of energy is at right angles to the movement of the vibration is __________. a. compression wave b. longitudinal wave c. transverse wave d. sound wave 3. Wavelength of a transverse wave is measured from __________. a. one compression point to the next rarefaction point b. the equilibrium position to the to crest or trough c. one crest to the next crest or from one trough to the next trough d. one crest to the next trough 4. Adding energy to a wave __________. a. decreases the amplitude b. does not affect the amplitude c. negates or cancels the amplitude d. increases the amplitude 5. If 200 waves hit our ankles in 2 minutes, the frequency of the wave is __________. a. 100 Hz b. 1.7 Hz c. 0.6 Hz d. 400 Hz 6. Period of a wave is the measure of __________. a. how many waves pass through in one cycle b. how much time it takes for one wave to cycle to pass a given location c. how many waves pass through in a given time d. how much energy a wave has

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7. If a wave travels 600 meters in 2.5 minutes, then the speed of the wave is __________. a. 3 meters/second b. 4 meters/second c. 240 meters/second d. 120 meters/second 8. Angle of a reflected wave will be _________________ the incident wave. a. smaller than b. larger than c. more scattered than d. the same as 9. Diffusion of light is most likely to occur when a wave encounters a surface that is __________. a. rough and dull b. smooth like a mirror c. smooth and shiny d. transparent like glass 10. What happens when waves passes from one medium to another? a. Nothing. b. They gain energy. c. They reflect. d. Their speed changes. 11. Black colored objects ___________________, white colored objects __________________, and transparent objects __________________ light. a. absorb, reflect, transmit b. absorb, transmit, refract c. transmit, refract, reflect d. reflect, absorb, transmit 12. Ability of a traveling wave to move or bend around an object, change direction, and continue to travel is called __________. a. refection b. diffusion c. refraction d. diffraction

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13. In constructive interference __________. a. two waves traveling toward each other overlap and form a smaller new wave b. two waves traveling toward each other overlap and form a wave with higher energy c. two waves traveling toward each other overlap and form a wave with lower amplitude d. two waves traveling toward each other overlap and form a wave with lower energy 14. The perceived effect of progressively increasing and or decreasing frequency as a result of a moving wave generator is called the __________. a. Coriolis Effect b. Doppler Effect c. El Nino Effect d. Constructive Interference 15. This type of wave requires a medium to travel through. a. Electromagnetic wave. b. Radio wave. c. Sound wave. d. Gamma wave. 16. Loudness of a sound depends on its __________. a. frequency b. wavelength c. energy d. period 17. Which one of the following is not an electromagnetic wave? a. Gamma wave. b. Microwave. c. Radio wave. d. Sound wave. 18. Electromagnetic waves are created by __________. a. particles of air vibrating back and forth b. the oscillation of charged particles c. coming together of a magnetic and electrical force d. air moving over the vocal cords

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19. Which one of the following shows the correct order of electromagnetic waves with increasing frequencies? a. Microwaves, Visible light, X-rays, Gamma Rays. b. Gamma Rays, Radio waves, Visible light, X-rays. c. Radio waves, Infrared waves Microwaves, Ultraviolet waves. d. Infrared waves, Microwaves, Radio waves, X-rays. 20. A rubber ball, that appears red in sunlight, is illuminated only by a blue light. What color does the ball appear to be under this illumination? a. Red. b. Blue. c. Black. d. White. 21. Which one of the following statements is true for plane mirrors? a. The image appears to come from behind the mirror, is the same size as the object, and is upright. b. The image appears to come from behind the mirror, is the same size as the object, and is real. c. The image formed is in front of the mirror, smaller than the object, and upside down. d. The image formed is right side up, real, and smaller than the object. 22. When light moves from lower to higher refraction index medium at an angle a. The light bends away from the normal. b. The light travels parallel to the normal. c. The light bends toward the normal. d. The light travels perpendicular to the normal. (Answer Key: 1.b, 2.c, 3.c, 4.d, 5.b, 6.b, 7.b, 8.d, 9.a, 10.d, 11.a, 12.d, 13.b, 14.b, 15.c, 16.c, 17.d, 18.b, 19.a, 20.c, 21.a, 22.c)

PART IV PHYSICAL SCIENCES (CHEMISTRY)

Chapter 11

PERIODICITY Martha Kurtz

The periodic table is a useful tool for correlating the physical and chemical properties of the elements. When the elements are listed in order of increasing atomic number (number of protons in the nucleus) repeating patterns in the physical and chemical properties of the elements can be readily observed. Mendeleev noticed these patterns and used them as a basis for the structure of the modern periodic table of the elements (as shown Figure 11.1). The arrangement of the elements in the periodic table allows us to make reasonably accurate predictions about their physical and chemical properties.

PHysical Periodicity Several physical properties of the atoms of each element can be predicted relative to other elements by combining two important concepts that form the basis for understanding why the periodic properties appear the way they do. These concepts are nuclear charge and shielding effect. The following sections briefly describe these concepts so that they can be used to explain the periodic trends that they affect.

nUclear cHarge

The nuclear charge of an atom is exactly what it sounds like, the charge of the nucleus of the atom. The nucleus is made up of protons and neutrons, and since protons have a positive charge while neutrons are neutral, the nuclear charge of an atom is equal to the number of protons contained in the atom. On the periodic table that means that the nuclear charge increases as you move across a period

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Figure 11.1 Periodic Table (Source: Eformulae.com—copied with permission)

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(row) because as you go from one atom to the next you are adding a proton. For example, the nuclear charge for a lithium (Li) atom is 3 while the nuclear charge for a neon (Ne) atom is 10.

sHielding effect

The outer shell electrons, the ones that participate in chemical bonding, are shielded from the charge of the nucleus by the inner shell electrons. Inner shell electrons weaken the attraction between the outer shell electrons and the nucleus. Let’s use lithium (Li) and neon (Ne) for examples. Lithium has two electrons in the first shell and one electron in the second shell (as shown in Figure 11.2). The one outer shell electron experiences “shielding” from the nuclear charge.

e e

e

+3

e

+3 Actual nuclear charge -2 Inner shell electrons shielding +1 Effective nuclear charge

e

e

e

+10

e e

Lithium

e e e

e Neon

+10 Actual nuclear charge -2 Inner shell electrons shielding +8 Effective nuclear charge

Figure 11.2 Nuclear charge, shielding, and effective nuclear charge for lithium and neon (Drawing by Martha Kurtz)

In neon there are also two inner shell electrons shielding the eight outer shell electrons. The electrons in the outer shell experience less than the full nuclear charge. The reduced charge felt by the outer shell electrons is called the effective nuclear charge and is roughly equal to the total nuclear charge minus the number of electrons in the inner shells. Lithium’s outer shell electrons experience an effective nuclear charge of +1 while neon’s outer shell electrons feel an effective nuclear charge of +8. Combining the concepts of nuclear charge and shielding effect to determine the effective nuclear charge forms the basis for the periodicity seen in the elements. There are three important periodic properties to consider and they are as

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follows: (a) the size of the atom, (b) ionization energy, and (c) electron affinity. All of these together help to explain why some elements are more reactive than others.

size of tHe atoM

The size of the atom depends on the number of electrons and the number of protons in the atom. Because electrons and protons are oppositely charged, the protons attract the electrons. The greater the number of protons, the greater pull they have on the electrons. The closer the electrons are pulled to the nucleus, the smaller the atom. Now let’s apply what we know about nuclear charge, shielding effect, and effective nuclear charge. What happens to effective nuclear charge as you move across a period (row) on the periodic table? As you move from one element to the next in a period, one proton and one electron are added. The proton adds to the nuclear charge. The electron is added to the outer most shell. Thus, the shielding effect remains the same and the effective nuclear charge increases by one for each step across the periodic table. The greater the positive charge felt by the outer shell electrons, the closer they will be pulled to the nucleus, and the smaller the atom will be.

Ionization energy

llic Meta

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char

Ionization energy

m

Non

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Electron affinity

Atomic radius

Electron affinity

Atomic radius

Figure 11.3 General periodic trends. (Public Domain)

What happens to the size of the atoms of each element as you move down a group (column) on the periodic table? Consider where the electrons are being added. From the top of the group to the bottom, the outermost electrons of the elements are located in shells successively further from the nucleus. For example, sodium (Na) has two electrons in the first shell, eight electrons in the second shell, and one electron in its outer shell, the third shell. Cesium (Cs) on the other hand,

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has 54 electrons in its inner shells and one electron in its outer shell, the sixth shell. The effective nuclear charge is essentially the same for sodium and cesium but cesium’s outer shell electrons are much farther from the nucleus. Physics tells us that the electric force weakens rapidly with increasing distance. Therefore, the attractive force on the outer shell electrons in a large atom such as cesium is much weaker than the attractive force on the outer shell electrons in a smaller atom such as sodium. Combining the trend in size across the periodic table with the trend down the table, you find that, in general, the atoms of the elements in the upper right hand corner of the periodic table are smaller in relation to the elements in the lower left hand corner. Predicting the relative size of the atoms of two elements is as simple as looking at where the two elements are on the periodic table. The smaller atoms will be above and to the right (as shown in Figure 11.3). Be sure you can make accurate predictions and also that you understand why one atom is smaller than another.

ionization energy

Another periodic trend based on nuclear charge and shielding effect is ionization energy. Ionization energy is the energy required to pull an electron from an atom to form an ion. Considering what you already know about effective nuclear charge, you can probably figure out the periodic trend for ionization energy. The elements with the strongest attraction between the protons and the outermost electrons will be the elements with the highest ionization energy. For example, sulfur (S) has a larger effective nuclear charge than sodium (Na); therefore, sulfur has a larger ionization energy than sodium. Within a family on the periodic table, a similar explanation can be made. For the same reason that the size increases as you go down, ionization energy decreases. Cesium (Cs) has a smaller ionization energy than sodium (Na) because cesium has much larger atoms that have a small attraction between the nucleus and the outer shell electrons. Remember that the outer shell electron in cesium is in the sixth shell while the outer shell electron in sodium is in the third shell. As with atomic size, combining the trend in ionization energy across the periodic table with the trend down the table, an overall trend emerges. In the case of ionization energy the atoms of the elements in the upper right hand corner of the periodic table have a larger ionization energy in general in relation to the elements in the lower left hand corner. Predicting the relative ionization energy of the atoms of two elements involves simple observations of where the two elements are on the periodic table. The atoms with smaller ionization energy will be below and to the left (as shown in Figure 11.3). Thus, the trend is the opposite of atomic size the smaller the atom, the larger the ionization energy.

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electron affinity

Electron affinity can be thought of as the opposite of ionization energy. It is the energy required to add an electron to an atom. The trend for electron affinity across the periodic table can be explained in much the same way as the ionization energy. Moving across the periodic table results in atoms with a greater effective nuclear charge (greater attraction for the outermost electrons) and, therefore, a greater attraction for a new electron and a larger electron affinity. Moving down the periodic table results in atoms with the same effective nuclear charge but outer shell electrons in larger shells. This results in a weaker attraction for the outermost electrons and, therefore, a smaller attraction for a new electron and a small electron affinity. There are many exceptions to the general trend in electron affinity, so without looking at the actual energies required to add an electron, the best we can do is make a prediction based on the trend. Again, combining the trend in electron affinity across the periodic table with the trend down the table, you get an overall trend. In the case of electron affinity, the atoms of the elements in the upper right hand corner of the periodic table generally have a larger electron affinity in relation to the elements in the lower left hand corner. Predicting the relative electron affinity of the atoms of two elements is, again, easily accomplished by looking at where the two elements are on the periodic table. The atoms with smaller electron affinity will be below and to the left (as shown in Figure 11.3). Thus, the trend is the opposite of atomic size and the same as ionization energy because the smaller the atom, the larger the ionization energy and the larger the electron affinity.

cHeMical Periodicity The patterns in chemical properties found in the periodic table are caused primarily by the number of electrons contained in each atom of the element. In particular, it is the number of electrons in the outermost shell of the atom that is important. Atoms that contain the same number of electrons in their outermost shell have similar chemical properties. This is because the electrons interact to form chemical bonds so elements with the same number of electrons will form the same kinds of bonds. For example, magnesium (Mg) and calcium (Ca) are both metals that have two electrons in their outmost shell. They both form a compounds containing one metal atom and one oxygen (O) atom (MgO and CaO). Carbon (C) and silicon (Si) are both nonmetals which have four outer shell elections and they both form compounds containing one nonmetal atom and two oxygen atoms (CO2 and SiO2). Magnesium and calcium belong to the same chemical group and occur in the same column of the periodic table. Carbon and silicon belong to a different chemical group, and occur in a different column. Much of the chemical behavior of an element can be predicted from its position in the periodic table. Historically, once he had devised the periodic table, Dimitri Mendeleev was able to predict the chemical properties of elements yet to

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be discovered by looking at the chemistry of the nearby elements. Since chemical bonds are formed by transferring or sharing electrons, how strongly a nucleus is able to attract the outermost electrons in an atom is important in determining the chemical behavior of the atom. Atoms with low ionization energy do not have a strong attraction between the nucleus and the outermost electrons. They can easily give up an electron. Elements that easily lose an electron to form positive ions are called metals. The easier it is to remove an electron from an atom the more reactive it is and the more metallic character it has. Atoms with high electron affinity have a very strong attraction between the nucleus and the outermost electrons. They can easily add an electron. Elements that easily add an electron to form negative ions are called nonmetals. The easier it is to add an electron to an atom the more reactive it is and the more nonmetallic character it has. As with the other periodic trends, chemical reactivity can be predicted by looking at the relative position of the elements on the periodic table. Because of the trends in metallic and nonmetallic character the most chemically active metal is on the lower left hand side of the periodic table and the most chemically active nonmetal is on the upper right hand side of the table (as shown in Figure 11.3).

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review QUestions—cHaPter 11 1. Which of the following will form chemical compounds similar to chlorine (Cl)? a. S b. Ar c. Br d. O 2. Of the following, which has the largest atomic radius? a. B b. C c. N d. F 3. Which of the following has the smallest atomic radius? a. O b. F c. P d. S 4. Which arrangement is in order of increasing atomic size? a. Tl, Sn, Ge, P b. Tl, Ge, Sn, P c. Ge, Sn, P, Tl d. P, Ge, Sn, Tl 5. An electron in the outermost occupied shell of which element experiences the greatest effective nuclear charge? a. Na b. K c. Rb d. All experience the same effective nuclear charge. 6. Which arrangement is in order of increasing first ionization energy? a. S, Si, P, Al b. Al, P, Si, S c. S, P, Si, Al d. Al, Si, P, S

Periodicity

7. Which of the following has the largest ionization energy? a. Sn b. Pb c. P d. As 8. Which of the following elements has the greatest (most negative) electron affinity? a. C b. O c. Si d. S 9. Indicate with of the following elements should have chemical properties similar to those of oxygen (O): a. N b. F c. S d. Cl 10. Which element should be most reactive? a. Rb b. Cs c. Sr d. Ba 11. What are the columns in the Periodic Table called? a. Series. b. Systems. c. Groups. d. Periods. (Answer Key: 1. c, 2. a, 3. b, 4. d, 5. d, 6. d, 7. c, 8. b, 9. c, 10. b, 11. c)

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Chapter 12

THE MOLE AND CHEMICAL BONDING William Loffredo

Mole concePt and cHeMical coMPosition In the early 1800’s John Dalton formulated the first Atomic Theory used by scientists. He collected and analyzed scientific data from his peers in order to form the theory. This was a great example of how the scientific method is used. The Atomic Theory had several postulates associated with it, including the following: (a) the atom is the smallest part of matter and (b) atoms of the same matter source behave similarly but differ from atoms from another matter source. The difficulty at the time of Dalton’s theory was that the amount of matter could only be measured in mass terms. There was no way of understanding the amount of matter on the atomic level, until Avogadro’s discovery. Amadeo Avogadro was studying the properties of gases and he made an observation that would solve this dilemma. As he studied the amount of gases and their respective volumes, he noticed that there was a direct relationship between the amount of gas and its volume. He used a standard set of temperature and pressure values for the gases and made the volumes equal to 22.4 L. If he treated the pure gases as parts (atoms or molecules, depending on the composition of the gas), he calculated that the amount of gas parts in the container was the same, 6.02x1023. This became known as Avogadro’s Number. This is a very large number, so large that we could not count this far in a lifetime. It is therefore not a practical number to use to measure the amount of matter, so we formed a definition. We say that Avogadro’s Number of parts (atoms or molecules) is equal to one mole. So the chemical mole is nothing more than a unit that describes the amount of matter. We reserve this unit for very small parts

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like atoms or molecules. It is not the unit we use in the laboratory for measuring amounts of matter because of the different atomic and molecular masses of the substances involved.

cHeMical forMUlas With Avogadro’s Number we have the necessary tools to understand the reactions Dalton and his peers observe because we can explain them in terms of the mole. We can do this because the mole is simply a term that describes a large number of parts, much like a dozen is used to describe 12 objects. So to apply this understanding to chemical composition, let’s look at the chemical equation for the formation of water. 2 H2 + O2 = 2 H2O What this equation tells us is that 2 hydrogen molecules, represented as H2, combine chemically with 1 oxygen molecule, O2, to form 2 molecules of water, H2O. Since molecules are so small, we will need to use a large number of them in order to do the experiment. So we will make use of the definition of the mole. In terms of the mole, this equation tells us that we have 2 moles of hydrogen molecules reaction with 1 mole of oxygen molecules to form 2 moles of water. So we see that we can discuss chemical formulas in terms of individual atom ratios or by mole ratios. Let’s look at an example of this concept. In each of the chemical formulas below discuss the element ratios in terms of atoms and moles (using one mole of the compound). NaHCO3: Atom ratios in 1 molecule of NaHCO3: 1 sodium atom to 1 hydrogen atom to 1 carbon atom to 3 oxygen atoms Mole ratios in 1 mole of NaHCO3 molecules: 1 mole of sodium atoms to 1 mole of hydrogen atoms to 1 mole of carbon atoms to 3 moles of oxygen atoms.

tyPes of Bonds The three main types of bonds include metallic, ionic, and covalent, with ionic and covalent being the most common. A metallic bond is the type of bond between metal atoms. The electrons are free to move around the various metal nuclei. The electrons are described as a “sea.” In an ionic bond the ions (charged atoms) make up a three dimensional array of alternating positive and negative ions (as shown in Figure 12.1). The ions are formed from the transfer of electrons from the metal atoms to the nonmetal atoms. The metal atoms then become positive ions (cations) and the nonmetals become the negative ions (anions). The cations are attracted to the anions through what are called an electrostatic attractions (opposite charges attract each other).

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Covalent bonds are formed as two or more nonmetal atoms share electrons with one another (as shown in Figure 12.1). An everyday analogy of this type of bond is the game of tug-of-war in which the electrons are represented by the rope and the teams are represented by the atoms. Most organic molecules are classified as covalent molecules. This is due to the fact that the skeletal foundation is the carbon-carbon bonds (recall that carbon is a nonmetal). Ionic Transfer Na+1

Cl

Na

[ Cl ]

-1

electron transfer

Covalent Sharing H

H

Cl

Cl

electron sharing

Figure 12.1 Ionic and Covalent Bonds (Drawing by William Loffredo)

electron dot and strUctUral forMUlas G.N. Lewis proposed a way of writing chemical structures using dots to represent the valence electrons that surround atoms. Valence electrons are those electrons in the outermost energy shell or level of the atom. These energy shells are often not filled and bonding between two or more atoms will fill the shells and create a stable substance. If we limit our discussion to representative elements on the periodic table, it turns out that the group number is equal to the number of valence electrons. While the core electrons (those electrons in filled shells) and the nucleus are involved in bonding, the valence electrons are most involved. Lewis arranged the valence electrons around the atomic symbol in pairs, since electrons are found in pairs. Below is a table showing the electron dot configurations of some of the atoms on the periodic table.

Table 12.1 Lewis Electron Dot Structure for some representative elements. Grp IA

Grp IIA

Grp IIIA

Grp IVA

Grp VA

Grp VIA

Grp VIIA Grp VIIIA

H

He

Li

Be

B

C

N

O

F

Ne

Na

Mg

Al

Si

P

S

Cl

Ar

K

Ca

Br

Kr

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Atoms will bond to each other in such a way as to become stable and this occurs when the valence energy shells are filled. Often that means that they have eight electrons in their valence shell (known as the octet rule). The octet rule came about from the observations that the noble gases are naturally stable and for the most part have eight electrons in their valence shell. When other types of atoms achieve the same number of electrons in their outer shells as the noble gases, we say that they are isoelectronic with the noble gases. Hydrogen is a notable exception to this rule. Since hydrogen can only accept two electrons in its energy shell, it is limited to one covalent bond or two electrons as an ion and is isoelectronic with the noble gas helium. In forming ionic compounds there is a transfer of electrons from the least electronegative element (the metal element, those found on the left-hand side of the periodic table) to the more electronegative element (the non-metal element, those found on the right-hand side of the periodic table). This transfer occurs due to the electron affinity of the non-metal elements and the low ionization energies of the metal elements. The number of electrons transferred depends on the electron configuration of the element and how many electrons the atom will need to gain or lose to be isoelectronic with the nearest noble gas. When forming covalent compounds, the bonding occurs between two nonmetal elements. The sharing of electrons between two atoms creates a bond, in which the sharing of two electrons constitutes a single bond, four electrons share a double bond, and six electrons share a triple bond. The number of pairs of electrons surrounding the atoms in the molecule usually follows the octet rule, except for hydrogen. There is a systematic way of drawing the Lewis Dot Structures for simple ionic and covalent molecules. Each structure consists of a central atom, usually given first in the formula (except if it is hydrogen), and the bonded atoms. Any electrons not involved in the bonding are referred to as nonbonding electrons. Remember that the total of the bonding and nonbonding electrons usually adds up to 8, except for hydrogen. Another aspect of the Lewis Dot Structure is the three-dimensional arrangement of the electrons surrounding the central atom. The theory that helps us predict the shapes of the molecules is called the Valence Shell Electron Pair Repulsion theory (VSEPR). The premise behind this theory is that the electrons are negatively charged and repel each other; therefore, the molecule will try to keep the electrons as far away from each other as possible. Figure 12.2 below provides several examples of Lewis Dot Structures and their various molecular shapes according to the VSEPR theory. Example 1: HCN The Lewis Dot Structure is shown and the VSEPR shape is linear.

H

C

N

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The Mole and Chemical Bonding

Example 2: H2O The Lewis Dot Structure is shown and the VSEPR shape is angular or bent.

H

O H

Example 3: NH3 The Lewis Dot Structure is shown and the VSEPR shape is trigonal pyramidal.

H

N

H

H

Example 4: CH4 The Lewis Dot Structure is shown and the VSEPR shape is tetrahedral.

H H

C

H

H

Figure 12.2 Sample Lewis Dot Structure (Drawing by William Loffredo)

In Lewis Dot Structures the dots represent the valence electrons surrounding the atom and are termed nonbonding electrons while the lines represent the bonding electron pairs (each bond or line in a structure stands for 2 electrons). In some depictions, the bonding electrons are not represented by lines but pairs of dots found in-between the two atoms being bonded. The driving force for the bonding patterns relates back to the octet rule in which each atom will have 8 electrons surrounding it, whether bonding or nonbonding, so that it can have a valence electron shell isoelectronic with a noble gas configuration and achieve stability.

systeMatic noMenclatUre of inorganic coMPoUnds Let’s turn our attention to naming the various molecules and compounds that we see in chemical reactions and in everyday life. We can divide the formulas into the following two broad categories: (a) inorganic compounds and (b) organic compounds. Traditionally, the term inorganic referred to substances that originated from nonliving matter such as rocks and minerals. Since living matter consists mostly of carbon, hydrogen, and oxygen, molecules comprised mostly of these elements are labeled organic while those consisting of metals and various other nonmetal elements were labeled as inorganic. With this in mind, SO3, which consists of sulfur and oxygen, would be classified as inorganic because it is not made up of carbon, hydrogen and oxygen. NaHCO3 consists of a metal (sodium) and carbon, hydrogen, and oxygen. The

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presence of the sodium atom makes it inorganic, even though it contains carbon, hydrogen, and oxygen, because metal-nonmetal element combinations are generally inorganic. Inorganic compounds can be further divided into four subcategories, including ionic inorganic compounds, simple binary ionic inorganic compounds, polyatomic ionic inorganic compounds, and covalent inorganic molecules. Each of those subcategories will be discussed below.

ionic inorganic coMPoUnds

Ionic inorganic compounds are composed of two ions—a positive ion called the cation and a negative ion called the anion. The first element listed in the formula is a metal and the second is nonmetal. You will need to remember some of the elemental symbols for metals in order to identify that the formula you see is ionic in nature. The most common are Li, Na, K, Mg, Ca, Ba, Al, Cu, Fe, Pb, Ag and Au. If you have a periodic table, then the locations of the metal elements can be found by drawing a diagonal line from B, boron element number 5, to Rn, radon element number 222. All the elements listed underneath (to the left of) the diagonal line are metals and those above (to the right of) the diagonal line are nonmetals. Notice that the majority of the elements on the Periodic Table are metals.

siMPle Binary ionic inorganic coMPoUnds

The term “simple” in simple binary ionic inorganic compounds refers to the fact that the two parts of the formula are ions, each consisting of only one element (e.g., NaCl or MgBr2). The term “binary” refers to the fact that only two elements are involved in the formula. The cation (metal element) is always listed first in the formula. This is an easy way to decide if an unknown formula represents an simple binary ionic inorganic compound or not. The metal ion is listed first and is named as its elemental name. The nonmetal ion undergoes a name change to signal that it is now bonded to the metal. The nonmetal names will all end with the suffix “ide.” Group VA N-3 is nitride P-3 is phosphide

Group VIA O-2 is oxide S-2 is sulfide

Group VIIA F-1 is fluoride Cl-1 is chloride Br-1 is bromide I-1 is iodide

Name the following Simple Binary Inorganic Ionic Compounds: KBr potassium bromide

MgI2 magnesium iodide

Ag2S silver(I) sulfide

Cu3P2 copper(II) phosphide

AlCl3 aluminum chloride

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The Mole and Chemical Bonding

PolyatoMic ionic inorganic coMPoUnds

Next we will consider polyatomic ionic compounds. The nomenclature rules are the same as for the simple binary ionic compounds, except that the ion is not a simple ion (one kind of atom); rather, it consists of a group of atoms that carry a charge. Below you will find some of the more familiar polyatomic ions, their names and their charges. NH4+1 ammonium ion OH-1 hydroxide ion CN-1 cyanide ion C2H3O2-1 acetate ion -1 -1 NO3 nitrate ion HCO3 hydrogen carbonate (bicarbonate) -2 CO3 carbonate SO4-2 sulfate PO4-3 phosphate When writing a compound formula that contains polyatomic ions and more than one of them is needed, you must use parentheses to ‘rope it off’ and then place the correct subscript outside the parentheses. Name the following Polyatomic Ionic Inorganic Compounds: KCN potassium cyanide

Mg(NO3)2 magnesium nitrate

AgOH silver(I) hydroxide

Cu3(PO4)2 copper(II) phosphate

NaHCO3 sodium hydrogen carbonate

covalent inorganic MolecUles

The difference between covalent inorganic and ionic inorganic compounds is that inorganic ionic compounds begin with a metal atom and covalent molecules start with a nonmetal atom. When naming inorganic covalent molecules, you will notice that both of the elements in the formula are nonmetals. Since the bonding between them is not based on ionic attractions, the nonmetals do not have charges. The atom ratio in the formula is indicated by the use of Greek numerical prefixes, shown in the table below. Table 12.2 Greek Numerical Prefixes

mono (1) (used rarely) di (2)

tri (3)

tetra (4)

penta (5)

hexa (6)

octa (8)

nona (9)

deca (10)

hepta (7)

The formula name consists of two parts just like the simple binary ionic. The first atom is just the elemental name, with the appropriate numerical prefix followed by the second atom named just like the ionic anion name (the root word ending in ‘ide’) and again with the appropriate numerical prefix.

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137

Name the following simple binary inorganic covalent molecules: CBr2 carbon dibromide

NI3 nitrogen triiodide

F2O difluorine oxide

S3O2 trisulfur dioxide

PCl3 phosphorus trichloride

noMenclatUre of siMPle organic coMPoUnds As stated above, covalent organic molecules will also begin with a nonmetal atom. What determines if a molecule is organic? Recall that the general rule is if the majority of atoms in the formula consist of carbon and hydrogen, then it is most likely organic in nature. An organic molecule may also have oxygen, nitrogen, phosphorus, sulfur, and halogen atoms, but they are usually minor components of the formula. The following formulas represent organic molecules: CH4 (methane, natural gas), C3H8 (propane, gas grills), C4H10 (butane, disposable lighters), C8H10N4O2, (caffeine) and C27H46O (cholesterol). Notice that the majority of atoms in each of these compounds are carbon and hydrogen. The reason that a majority of atoms in organic compounds are carbon and hydrogen atoms is that organic molecules are derived from living matter and carbon and hydrogen are the major components of living matter. So it is easy to distinguish an organic molecule from an inorganic one by virtue of the fact that there are usually more carbon and hydrogen atoms in the organic one. Classify the formulas below as organic or inorganic: NaHCO3 inorganic

C6H5NO2 organic

C20H30O organic

N2O5 inorganic

C6H12O6 organic

Organic molecules are subdivided into a variety of categories based on their function. The focus here will be on the three simple types of organic molecules known as hydrocarbons. Hydrocarbons consist of alkanes, alkenes and alkynes. The Lewis Dot Structure of alkanes contain all carbon-carbon single bonds which usually results in the maximum carbon to hydrogen ratio. The maximum ratio fits the formula CnH2n+2, where n is any integer. The carbon atoms of alkanes can be connected in a straight line fashion and are referred to as straight-chained alkanes. Alkanes can also have the carbon atoms in a ring structure and are referred to as cycloalkanes as well as carbon branches (branched alkanes). Branched and cyclic structures can also be found in the other types of hydrocarbons. Alkane names will end in the suffix “ane,” reflecting that all the bonds are single bonds between the carbon atoms. The number of carbons in the skeleton structure is reflected in the parent name of the molecule. This is true for all organic molecules. The Lewis Dot Structures for the first four hydrocarbon alkanes are shown on the following page.

The Mole and Chemical Bonding

138 H methane, CH4

H

C

H propane, C3H8

H

H

H

C

H H C H C H H

H ethane, C2H6

H C H

H H

H

C

H butane, C4H10

H

H

H C H

H H C H C H C H H H

Figure 12.3 Alkane Structures (Drawing by William Loffredo)

Alkenes are hydrocarbons that contain at least one multiple bond. This will show up in the structure as a double bond (alkene). Alkene names end in the suffix “ene.” and the carbon skeleton structure is the parent name. The presence of a functional group only changes the suffix ending of the molecule name. The Lewis Dot Structures of some alkenes are shown below. H

H ethane, C2H4

C

C

H

H

H

H

propene, C3H6

C

C

H C H H

H

H H butane, C4H8

C

C H

H

C H

H C H H

Figure 12.4 Alkene Structures (Drawing by William Loffredo)

Alkynes are also hydrocarbons that contain at least one multiple bond but this will show up in the structure as a triple bond. Alkynes will end in “yne” and the carbon skeleton structure is still the parent name, just like alkenes. The Lewis Dot Structures of some alkynes are shown below. ethyne, C2H2

H

C

C

H

propyne, C3H4

H

C

C

H C H H

The Mole and Chemical Bonding butyne, C4H6

H

C

C

H C H

H C H H

Figure 12.5 Alkyne Structures (Drawing by William Loffredo)

139

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The Mole and Chemical Bonding

review QUestions—cHaPter 12 1. The term mole is a term used to a. describe a biological specimen. b. describe very large atoms and molecules. c. describe the amount of matter in terms of atoms and molecules. d. measure out amounts of matter for scientific experiments on an analytical balance. 2. Which formula below has the ratio 2 sodium atoms to 3 oxygen atoms? a. NaHCO3 b. NaC2H3O2 c. Na2NO3 d. 3 Na2O 3. According to the balanced chemical equation below, how many moles of water can be formed from 3 moles of sulfuric acid, H2SO4? 2 NaOH(aq) + H2SO4(aq) = Na2SO4(aq) + 2 H2O(l) a. 3 moles of water. b. 1.3 moles of water. c. 1.5 moles of water. d. 6 moles of water. 4. Which formula listed below represents an inorganic ionic compound? a. BCl3 b. CoS c. CS2 d. BrF 5. Which formula below represents an inorganic covalent molecule? a. CaBr2 b. NaCN c. NaHCO3 d. P4S8 6. Which formula below represents an organic molecule? a. NaCN b. NaNO3 c. C6H12O6 d. KC2H3O2

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7. Which type of organic hydrocarbon molecule has at least one double bond in the carbon structure? a. Cycloalkane. b. Alkyne. c. Alkane. d. Alkene. 8. Which theory describes the three dimensional shape of molecules? a. The VSEPR theory. b. The Mole theory. c. The Lewis Dot theory. d. The scientific method. (Answers Key:1.c, 2.c, 3.d, 4.b, 5.d, 6.c, 7.d, 8.a)

Chapter 13

STATES OF MATTER Robert Cohen

ProPerties of solids, liQUids, and gases Many properties of matter can be explained via the atomic theory, which involves the following three important postulates: (a) all matter is composed of molecules, (b) the space the matter occupies (volume) is a function of the space between the molecules, and (c) molecules are in a constant state of motion. The molecules for each phase of matter (solid, liquid, gas) have a different motion. An example of a solid would be a rock. Unless you break the rock, it keeps the same shape. This is because the molecules that make up the rock are bonded to each other in a particular way, much like the way the parts of a house are all connected. To break a solid, you need to break a whole series of connections. An example of a liquid would be the milk in a glass. When you pour the milk from one glass to another, it takes on the shape of whatever glass it is poured into. The “size” of the milk, however, remains the same. As in a solid, the molecules that make up a liquid are also bonded to each other. However, the connections are not as strong. Consequently, the molecules are free to “slide” from one molecule to another, much like how a bunch of little spherical magnets can slide past each other yet still remain connected. Thus, a liquid takes the shape of its container whereas a solid does not. An example of a gas would be the air around us. In a gas, the molecules are not connected at all. Consequently, the gas is free to expand or contract to fill up whatever container it is in. Although we cannot see gases, we can still “feel” gases via the temperature and the pressure. The temperature of a gas corresponds

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to the average kinetic energy of the molecules that make up the gas. This can be measured by a mercury thermometer because, as the gas molecules hit the thermometer, some energy is transferred between the gas and the mercury inside the thermometer, making the mercury cool and contract (if the gas is cooler) or warm and expand (if the gas is warmer). The pressure of a gas is related to the force exerted by the gas (per area) on objects. Air exerts a pressure on us in all directions, but normally we are oblivious to the air pressure because we only notice when there is a difference in pressure. For example, if you stick your hand out of a car window when the car is not moving, the air pressure exerted by the air on the palm side is equal to the air pressure exerted on the back-hand side. Consequently, you don’t experience a force on your hand. However, if you stick your hand out the car window while driving down the street, the air in front of the hand is compressed slightly and, as such, the air pressure on that side of the hand is greater than the air pressure on the other side and you feel a force on your hand pushing your hand toward the back of the car. Some people experience ear pain as they move up or down in altitude (e.g., ascending or descending in an airplane). This is because it takes a while for the air inside the ear to change and match the air outside the ear. When the air outside exerts a different pressure than the inside the ear, there is pain or discomfort. When the air pressure equalizes, one experiences a “popping” sensation and the discomfort goes away.

PHase cHanges Solids, liquids and gases are able to change from one state or phase to another. For solids to change to liquids (melting) and liquids to change to gases (evaporation), the bonds between the molecules must be broken in some way. For gases to change to liquids (condensation) and liquids to change to solids (freezing), the bonds between the molecules must be formed in some way. For example, bonds are broken when liquid water evaporates to form water vapor (an invisible gas). The faster the liquid molecules are moving, the more likely they are to break those bonds. For this reason, evaporation is quicker when the liquid is warm than when it is cool. At the same time, as anyone who has felt cold coming out of a pool or shower can attest, evaporation is a cooling process, because energy is needed to break the bonds and that energy is taken from the environment. Since evaporation can occur at any temperature (i.e., it need not be above boiling), some water vapor is usually present in the air, regardless of the temperature. There is a limit to how much water vapor can be present, however, because of condensation. The greater the vapor pressure (i.e., the pressure exerted by the water vapor molecules), the more likely condensation will occur. When bonds form, energy is released, much like sound is produced when you let a north pole

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States of Matter

of a magnet “bond” with a south pole of another magnet. The energy goes into heating up the environment which is why condensation is a warming process.

crystals Snow is an example of the solid form of water. However, upon closer examination, snow does not look like a frozen drop of water. Instead, it looks like a tiny hexagonal crystal. The reason for the difference has to do with how snow forms. Rather than forming when liquid water freezes, snow is produced when the ice crystals form directly from the vapor. Just as there is a back-and–forth process between the liquid and vapor states (called condensation and evaporation), there is also a similar back-and–forth process between the vapor and solid states. The conversion from vapor to solid is called deposition and the conversion from solid to vapor is called sublimation. When liquid is frozen, it takes the form it had before it was frozen. Consequently, a frozen water droplet is round, not hexagonal. The deposition process, on the other hand, produces a crystal of a particular shape because the bonds form preferentially at particular points on the solid, based on the temperature and shape of the molecules. Water forms hexagonal crystals but other materials can form cubic or triangular crystals., A crystal can also form in other ways. For example, if one takes water that is saturated with table salt and then cools the solution, the sodium and chloride atoms that are separated within the salt water solution will “attach” to each other at certain points and form a solid with a cubic crystalline structure. A crystalline structure can also be produced if the liquid cools very slowly and/or under great pressure, so that the bonds form only at the preferential points.

tHe ideal gas law and tHe kinetic MolecUlar tHeory As you might suspect, temperature, pressure, and number of molecules per volume of a gas are related. If the temperature increases, the pressure also increases. One can also increase the pressure by increasing the number of molecules that are present per volume. The relationship between the three is called the ideal gas law. The reason it is called the ideal gas law, and not just the gas law, is because technically it only works for ideal gases. In the real world, there are no ideal gases. However, most gases, like air, are pretty close. To be an ideal gas, several conditions need to be met. There must be no attraction between the molecules at all, the collisions between the molecules must be completely elastic, the temperature must be proportional to the average kinetic energy of the molecules, and the molecules must be so tiny that we can consider them to have no volume themselves. These assumptions are part of the kinetic molecular theory. These postulates seem very unrealistic but it turns out that if a gas is composed of a huge number of molecules (but not so large that they are

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squeezed too close together) that are in constant, random motion, most of these postulates hold true. According to the ideal gas law, the three properties of temperature, pressure and number of molecules per volume are related. In fact, knowing two of them, one can determine what the remaining one must be. Similarly, if one property changes, at least one of the others must change as well. For example, for a particular number of molecules in a fixed volume, if one increases the temperature, the pressure will increase (as the molecules hit the walls with a greater speed). Likewise, for a particular temperature, if one increases the number of molecules within the fixed volume, the pressure will also increase (as more molecules are hitting the wall). It turns out that, for an ideal gas, the following ratio is constant for a particular gas:

P

( )

n T V

= R

The R represents the value of the ratio, P equals the pressure, n equals the number of molecules, V equals the volume, and T equals the temperature. This value is the same for all gases and is equal to 8.3144 J/mol/K. This number assumes that the temperature is measured in kelvin (K), the volume is measured in cubic meters (m3), the pressure is measured in pascals (Pa) and the number of molecules is measured in units of moles (where one mole is equal to 6.022×1023 molecules). For the air at sea-level, typical values would be a temperature of 273 K (0°C or 32°F) and a pressure of 101,325 Pa (1 atm or 14.7 lb/in2), where one mole of molecules would take up a space of about 0.0224 m3 (22.4 liters; a little less than one cubic foot).

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review QUestions—cHaPter 13 1. If a substance takes the shape of its container, but maintains a consistent volume, the substance is a a. solid. b. liquid. c. gas. d. crystal 2. Which of the following statements is true of air? a. Since air is a gas, it does not exert pressure on us. b. Air pressure only occurs when the air is moving. c. The force exerted by the air is the same on all sides of us so we don’t notice it. d. It only exerts a downward pressure on us. 3. When freezing, condensation, and deposition occur, a. energy is released from the substance into the environment. b. the substance absorbs energy from the environment. c. first energy is released and then absorbed by the substance. d. there is no energy transfer between the substance and the environment. 4. Suppose you have 3 moles of an ideal gas inside a fixed volume of 2 m3. The temperature is 0°C and the pressure is 1 atm. What happens to the pressure if the temperature is increased to 10°C? a. It increases to 1.04 atm. b. It increases to 3.0 atm. c. It remains the same at 1 atm. d. It decreases to 0.1 atm. 5. Can water vapor exist below the boiling point of water? a. No, because the temperature must be above boiling in order for water vapor to exist. b. Yes, but the vapor will quickly condense back to liquid. c. Yes, because evaporation is a cooling process and lowers the temperature below the boiling point. d. Yes, because water vapor can exist at any temperature.

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6. Why do ice cubes take the shape of the container, whereas snow crystals are hexagonal in shape? a. Snow crystals form on particles that are hexagonal in shape. b. Snow crystals are shaped by the wind into hexagonal shapes. c. Snow crystals form from water vapor deposition instead of liquid water freezing. d. Snow crystals are not made of pure water and so form crystals when they cool. (Answer Key: 1.b, 2.c, 3.b, 4.a, 5.d, 6.c)

Chapter 14

CHEMICAL REACTIONS Kenneth King

Balancing cHeMical eQUations A chemical reaction is a process that changes one set of substances into another set of substances. Chemical reactions occur when a piece of metal becomes rusty, when a piece of paper is set on fire, when an antacid table is dropped into a glass of water, and when food is digested. Chemical reactions are often contrasted with a physical change, which occurs when a substance undergoes a transformation in appearance or state. For example, cutting a board into two pieces is a physical change because the board remains composed of the same substance before and after the cutting. Water can be easily transformed from a solid state (ice) to a liquid state of water and on to a gas (steam) as heat energy is applied. These are examples of physical changes, because the water remains unchanged. Balancing a chemical equation is a straightforward process. The total quantity of matter present before chemicals are combined is required to match the total quantity present after the chemicals are combined. For example, hydrogen (H) and oxygen (O) may be combined to form water (H2O). Expressed in a sentence, the process can be represented as follows: hydrogen, combined with oxygen, produces water. A drawback of a sentence-based approach is that it is cumbersome to write this way, and it makes sense only if the reader and the writer of the sentence share the same language. Water, for example, is agua when written in Spanish. This relationship can be better represented by using chemical symbols to represent the parts of the reaction. Chemical symbols are used throughout the world and are independent of the language spoken locally. Many of the chemical sym-

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bols have their roots in Latin, such as the symbol for sodium, Na, which comes from the Latin natrium. The chemical equation that represents the creation of water is written below. Note the arrow that separates the products from the reactants. This emphasizes the direction in which the reaction takes place. In this case, hydrogen and oxygen combine to form water. H + O → H2O However, in addition to representing the total quantity of materials present before and after a reaction, the proportions of the materials present also need to be represented. The equation above represents the chemicals present in the reaction, but it does not accurately represent the quantity and proportions of chemicals present before and after the reaction. Note that on the reactants’ side of the equation (to the left of the arrow) there is a single H and O, for hydrogen and oxygen. Reactants are the chemicals that are combined at the start of a chemical reaction. On the right hand side of the equation, there are two hydrogen atoms present (H2) and a single oxygen atom (O), due to the way hydrogen and oxygen combines to form water. Balancing a chemical reaction is done to ensure that the quantity of reactants (H and O, in this case) match the quantity of products (H2O) generated. The products are the outcomes of the chemical reaction, and are placed on the right-hand side of the equation. Producing the needed balance is achieved by placing a number in front of the chemical symbol to scale it and represent the proportion of each atom needed before and after to achieve the needed balance. 2H + O → H2O While this achieves balance in one respect, it does not represent the way some atoms, such as oxygen and hydrogen, appear in nature. Gases such as hydrogen and oxygen are bound together in pairs of atoms called molecules. Oxygen atoms and hydrogen atoms are found free in nature paired up as oxygen and hydrogen molecules, O2 and H2, respectively. 2H2 + O2 → H2O One more step is needed to balance the relationship between the products and reactants. Note that there are two oxygen atoms (present as an oxygen molecule) on the products side. The number of water molecules on the left hand side of the equation needs to be doubled in order to achieve balance in the equation. This is represented in the following manner: 2H2 + O2 → 2H2O We can now check for balance using the following process. We can see that the equation is balanced because the number of atoms of each type is the same for the reactants as it is for the products (as shown in Table 14.1).

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150 Table 14.1 Oxygen Atoms

Reactant Side

Product Side

Equal?

Hydrogen Atoms

2 x H2 = 4 hydrogen

2 x H2 = 4 hydrogen

Yes

Oxygen Atoms

O2 = 2 oxygen

2O = 2 oxygen

Yes

Another example will help to make the process more understandable. Aluminum + Oxygen → Aluminum Oxide Represented as chemical symbols, this reaction becomes Al + O2 → Al2O3 To begin to balance the equation, it is necessary to start by balancing the number of aluminum atoms on both sides of the equation. 2Al + O2 → Al2O3 With two oxygen atoms counted among the reactants, and three among the products, we recognize that we need to balance the number of atoms on each side of the equation. It is not appropriate to use a fraction, so our next step is to multiply both sides by some small integer to produce the same number of oxygen atoms on both sides of the equation. 2Al + 3O2 → 2Al2O3 Now the aluminum atoms are unbalanced. We can remedy this by multiplying the number of Al atoms by a total of 4. 4Al + 3O2 → 2Al2O3 We can now check for balance using the following process: Table 14.2 Oxygen Atoms

Aluminum Atoms

Reactant Side 4 aluminum

Product Side 2 x Al2 = 4 aluminum

Equal? Yes

Oxygen Atoms

3O2 = 6 oxygen

2O3 = 6 oxygen

Yes

The main purpose for representing chemical reactions in this form is that it is much less cumbersome than using models of atoms and molecules. For example, using models of atoms and molecules to represent the formation of water from hydrogen and oxygen (as shown in Figure 14.1) is much more complicated than using a chemical formula.

Figure 14.1 Alternative representation for chemical reactions. (Drawing by Kenneth King)

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tyPes of cHeMical eQUations There are four types of chemical reactions and they include (a) synthesis reactions, (b) decomposition reactions, (c) single replacement reactions, and (d) double replacement reactions. In a synthesis reaction, two or more substances join together to make something more complex. They are of the general type A + B → AB. The reaction of hydrogen and oxygen combining to form water, shown above, is a reaction of this type. The two examples listed below are also synthesis reactions. 8Fe + S8 → 8FeS Na + Cl → NaCl A decomposition reaction is the opposite of a synthesis reaction. In this type of reaction, a complex substance breaks down into simpler pieces. These reactions are of the general form AB → A + B. The two examples listed below are also decomposition reactions. 2H2O → 2H2 + O2 Mg(NO3)2 → Mg(NO2)2 + O2 A single replacement reaction describes a chemical reaction in which a substance takes the place of one of the parts of a more complex substance. The general form for reactions of this type is AB + C → AC + B. The two examples listed below are also single replacement reactions. Mg + 2H2O → Mg(OH)2 + H2 Zn + 2HCl → ZnCl2 + H2 A double replacement reaction takes place when two complex substances switch subparts with each other. The model AB + CD → AD + BC represents this form. The two examples listed below are also double replacement reactions. Pb(NO3)2 + 2KI → PbI2 + 2KNO3 NaCl+ AgNO3 → NaNO3 + AgCl

endotHerMic and exotHerMic cHeMical reactions Exothermic reactions give off heat when the chemicals are combined. On a small scale, the reaction would feel warm to the touch if you were to come into contact with it. Many chemical reactions are exothermic in nature. These include burning paper, decomposition of organic matter into compost, and “heat packs” that are used to warm areas of the human body. Endothermic reactions absorb heat when the chemicals are combined. Unlike the exothermic reactions described above, an endothermic reaction would feel cool to the touch if you were to make contact with it. An instant cold compress, used in first aid and by sports trainers, is one example of an endothermic reaction. It feels cool to the touch because energy is being transformed from your body to the cold compress. Scientists often describe exothermic and endothermic reactions in terms of enthalpy. Enthalpy describes the total energy in a system. Energy, as you may

152

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recall, represents the potential to accomplish work. Enthalpy is represented in scientific language by the symbol H. The change in enthalpy, ΔH, is used to represent a decrease or increase in the system’s enthalpy. In an exothermic reaction, heat is released. The change in enthalpy, ΔH, is negative, representing the transfer of heat energy outside of the system. When the change ΔH is positive, we are observing an endothermic reaction. Energy is being transferred into the system from outside, a net transfer of energy into the system.

effects of teMPeratUre, PressUre, concentration, and catalysts on cHeMical reactions A number of factors effect chemical reactions. At the heart of each of these effects is the opportunity to increase the number of interactions among the chemicals being combined and thereby speed up the reaction. The Maxwell-Boltzmann Distribution (as shown in Figure 14.2) illustrates how temperature, pressure, and concentration influence chemical reactions.

Figure 14.2 Maxwell-Boltzmann Distribution (Drawing by Kenneth King)

Recall from the chapter on Mechanics that the energy of motion, kinetic energy, is described by the equation below. Ekinetic = ½ mv2 Since all of the molecules of a particular type of molecule have the same mass, the amount of kinetic energy depends only on the speed of the particles. All H2O molecules, for example, have nearly identical masses, so the kinetic energy present is related only to how fast the molecules are moving around. In a mixture of moving particles, the speed will vary a great deal. Some particles have lower energy and will move slowly, while others demonstrate their higher energy by moving rapidly. Most molecules will be close to the average speed for the system. The Maxwell-Boltzmann distribution shows how the speed of particles in a system changes for a given temperature.

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The most important point to for you to understand is that there are few molecules in the “high energy” part of the graph. Those particles that have energy values over a certain level, the activation energy, are more likely to react with other molecules. If a molecule does not have enough energy to place it in the shaded area, then it will not take part in the reaction. This is why temperature has a significant influence on chemical reactions. Temperature is a measure of the average kinetic energy (energy of motion) of the particles in a system. While the increased speed of particles causes an increase in the collision rate, this is not the main reason that the reaction rate increases. More important is the fact that a higher proportion of reactants have the necessary energy to take part in a chemical reaction. In the language of chemistry, rapidly moving molecules have sufficient activation energy to take part in a chemical reaction. Increasing the temperature of the system increases the number of particles that possess the required activation energy to react. Increasing pressure will also increase the rate of a chemical reaction in gases, but not in solids or liquids. The reason that this takes place in gases is that it is essentially the same thing as increasing the concentration of the chemicals, which leads to an increase in the likelihood of collisions between particles, resulting in a chemical change (as shown in Figure 14.3). Increasing the number of collisions between the particles increases the chances for the reactants to produce a chemical reaction.

Figure 14.3 Increase in pressure. (Drawing by Kenneth King)

This relationship can also be understood mathematically, using the ideal gas equation below: pV = nRT In this equation, p represents pressure, V represents volume, n is a measure of the numbers of particles present, R is a proportionality constant, and T represents the temperature. If the temperature remains constant than the equation can be rearranged in the following manner: n p = V x RT

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Chemical Reactions

Since RT is a constant, and the volume, V, remains the same, the pressure is directly proportional to the number of particles present, n. So, if you double the pressure the number of particles will be doubled, and the chances for particles to collide with each other is also doubled. Therefore, the reaction will take place more quickly. Concentration is an important factor in chemical reactions as well, because the more particles that are present, the more often particles will collide. The greater the number of collisions, the more likely it is that a reaction will take place. Increasing concentration can be achieved by adding more of one or more of the reactants. This increases the frequency with which collisions will take place (as shown in Figure 14.4).

Figure 14.4 Increase in concentration. (Drawing by Kenneth King)

A catalyst is a substance that increases the rate of a reaction. A catalyst participates in the reaction, but does not change chemically. A catalyst increases the rate of a reaction by lowering the activation energy required for the chemical reaction to move forward (as shown in Figure 14.5).

Figure 14.5 Activation Energy (Drawing by Kenneth King)

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155

In Figure 14.5, the graph represents the difference in the activation energy required for the reaction to commence between reactants X and Y. Without the catalyst, more energy is required for the reaction to take place. The catalyst accomplishes this feat by combining with the reactants to form short-term products that provide stepping stones to complete the overall reaction. The alternate pathway for the reaction to follow makes use of intermediate steps that each possesses a lower overall energy. The graph with the lower activation energy displays a reaction pathway that allows for a series of intermediate steps for the reaction to pass through, each with its own lower activation energy. These smaller activation energies provide a pathway for the overall reaction to proceed, but with a smaller activation energy needed for the reaction to commence. An example of a catalyst is provided below. In this reaction, H2SO4, also known as sulfuric acid, serves as a catalyst. Placing the catalyst over the arrow indicating the direction of the reaction is a customary way to note the presence of a catalyst. The ethanol (CH3CH2OH) is briefly converted into an unstable intermediate step, which reacts with Cl- to produce the products of the reaction (Senese, 2010). H2SO4 CH3CH2OH + HCl → CH3CH2Cl + H2O

Practical aPPlications of electrocHeMistry Electrochemistry is the field of chemistry that drives chemical reactions that involve either applying an external electric current to a solution or producing an electric current through chemical reactions. In electrochemistry, an electric current can either produce a chemical change or a chemical change can produce an electric current. Both approaches have many practical applications. Electroplating is one practical application of electrochemistry. In this process, an electric current passes through a chemical solution that conducts electricity. The source material provides a positively charged ion, drawn from the positively charged terminal, that enters the solution and is transferred to the opposite electric terminal (as shown in Figure 14.6). -+ e-

e-

Anode(+)

Cathode(-) Metal rod

Cu rod

Cu

Cu2+

SO42-

Figure 14.6 Electroplating (Drawing by Kenneth King)

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156

The solution is called the electrolyte. The terminal with the positive charge is referred to as the anode and the terminal with the negative charge is the cathode. Plating a metal cathode with the metal copper (Cu) offers a straightforward example of this process. Two pieces of metal are placed into a solution containing copper sulfate (CuSO4). One of the pieces of metal is made of pure copper. This piece of metal will serve as the source of copper to be used to cover the second piece of metal with copper metal. The piece of copper metal has a positive electrical charge and the second piece of metal has a negative charge. When an electric current passes through the electrolyte, copper atoms are removed from the copper anode. They are electrically attracted to the negatively charged cathode, and build up on the surface of the cathode. If an item, such as an eating utensil, was used as the cathode, that item would receive a coating of pure copper. Gold and silver plating of jewelry is one application of this process. Electrolysis can be used to break up a chemical as well. Water can be broken down into its component materials, hydrogen and oxygen, through the use of an electric current, (as shown in Figure 14.7). The addition of energy to the system causes the water molecule to separate into two separate molecules. The apparatus collects the gases formed in the collection tubes above the electrodes. Hydrogen gas forms at the negative terminal (cathode) and oxygen gas forms at the positive terminal (anode). Because there is a ratio of two atoms of hydrogen for each atom of oxygen in a water molecule, twice as much hydrogen gas is formed as oxygen gas. -+ e-

e-

Cathode(-)

Anode(+)

Hydrogen gas (H2) collects at negative terminal (cathode)

Platinum (Pt) terminals–Pt is a very nonreactive metal

Oxygen gas (O2) collects at positive terminal (anode)

H 2O

Figure 14.7 Electrolysis of water. (Drawing by Kenneth King)

Galvanic cells produce electric current through a chemical reaction between two metals (as shown in Figure 14.8). Because different metals have greater/lesser tendencies to release electrons, the movement of charges produces an electric current. The process takes place when a pathway is provided between the different metals. In the earliest examples, a paper disc soaked in salt water provided the pathway (Pilar, 1979).

Chemical Reactions

Metal

A different metal

157

Paper soaked in salt water

Figure 14.8 Voltaic Pile (Drawing by Kenneth King)

The diagram presented here shows how a series of metal discs sandwiched between layers of paper soaked in salt water forms a simple battery. This can be duplicated easily at home by inserting a one cent coin and a nickel into a citrus fruit. The fruit provides a conducting medium for the two metals, operating as a simple galvanic cell. In principle, a series of these fruit-coin cells can be combined to make a battery.

.

158

Chemical Reactions

review QUestions—cHaPter 14 1. The chemicals sodium hydroxide (NaOH) and sulfuric acid (H2SO4) are combined. They react and form the products sodium sulfate (Na2SO4) and water (H2O). Which of the equations below represents a balanced chemical reaction describing that reaction? a. NaOH + H2SO4 → Na2SO4 + H2O b. 2NaOH + H2SO4 → Na2SO4 + H2O c. 2NaOH + H2SO4 → Na2SO4 + 2H2O d. None of the above. 2. What coefficients should be used to balance this equation? __Mg + __O3 → __MgO + __Mn a. 3, 1, 3, 2 b. 3, 3, 3, 2 c. 1, 3, 3, 2 d. 3, 1, 1, 3 3. What coefficients should be used to balance this equation? __Fe + __NH4OH → __Fe(OH)3 + __NH4Cl a. 1, 1, 3, 3 b. 1, 3, 1, 3 c. 3, 1, 1, 3 d. 1, 1, 1, 3 4. What type of chemical reaction is S8 + 24F2 → 8SF6? a. Synthesis reaction. b. Decomposition reaction. c. Single replacement reaction. d. Double replacement reaction. 5. What type of chemical reaction is Zn + CuCl2 → ZnCl2 + Cu? a. Synthesis reaction. b. Decomposition reaction. c. Single replacement reaction. d. Double replacement reaction. 6. What type of chemical reaction is 2SO3 → 2SO2 + O2? a. Synthesis reaction. b. Decomposition reaction. c. Single replacement reaction. d. Double replacement reaction.

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159

7. What type of chemical reaction is Mg + HCl → MgCl2 + H2? a. Synthesis reaction. b. Decomposition reaction. c. Single replacement reaction. d. Double replacement reaction. 8. Increasing the pressure, temperature or concentration of a set of reactants increase the likelihood that the __________ of the system is more readily met. a. Potential Energy b. Activation Energy c. Thermal Energy d. None of the above 9. A catalyst provides a lower __________ to increase the rate of a chemical reaction. a. Potential Energy b. Activation Energy c. Thermal Energy d. None of the above 10. One aspect of using a catalyst in a chemical reaction is that the catalyst a. is consumed in the chemical reaction. b. is not present in the chemical reaction. c. creates intermediate steps in the chemical reaction with a higher activation energy. d. creates intermediate steps in the chemical reaction with a lower activation energy. 11. Electrochemistry represents a type of chemical reaction that involves the movement of charges through electric current. Which of the following is NOT an example of an electrochemical reaction? a. Electrolysis. b. Electroplating. c. Catalytic cells. d. Galvanic cells. 12. When describing a galvanic cell, which of the following is most true? a. The cell requires two different types of metal and a means of conducing the current, such as salt water. b. The cell requires two different types of metal and an insulating material, such as dry paper. c. The cell requires only one type of metal to generate the current, and a means of conducing the current, such as salt water. d. None of the above are accurate statements.

160

Chemical Reactions (Answer Key: 1. c, 2. a, 3. b, 4. a, 5. c, 6. b, 7. c, 8. b, 9. b, 10. d, 11. c, 12. a) Works Cited

Pilar, Frank L. 1979. Chemistry, the Universal Science. Reading, MA: Addison-Wesley Publisher. Senese, Fred. 2010. “What Are Some Examples of Reactions That Involve Catalysts?” General Chemistry Online: FAQ: Chemical Change: General Chemistry Online. Accessed February 15. 2010. http://antoine.frostburg.edu/chem/ senese/101/reactions/faq/examples-of-catalysts.shtml.

Chapter 15

SOLUTIONS AND SOLUBILITY T. Michelle Jones-Wilson

tyPes of solUtions All matter can be broadly classified as either a pure substance or a mixture. Solutions are mixtures because they involve the combination of a solvent and a solute (as shown in Table 15.1). The component present in the largest concentration is defined as the solvent, and the component or components present in smaller concentration(s) are termed the solute(s). If a solute dissolves in the solvent to provide a single phase which is homogeneous (of uniform composition) throughout, the solute is considered soluble in the solvent. It could be said that the solvent dissolves the solute. Solutes that do not dissolve or exceed their solubility are considered insoluble. Table 15.1 Solution Types

Solvent gas liquid liquid liquid solid

Solute gas gas liquid solid solid

Example air (a mixture of many gases) soda (carbon dioxide dissolved in water) mixed drink (alchohol and water) salt water (NaCl in water) alloys (steel)

The composition of a solution can include any of three physical phases—solid, liquid, or gas. Solvents can be further divided into two categories, depending on the differences in electronegativity values of the atoms in the solvent. Those

162

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with large differences are termed polar and those with small or no differences are termed non-polar. Liquid solvents can be further divided into two categories— aqueous and organic. Aqueous refers to solutions where water is the solvent, while the term organic refers to compounds containing carbon. Familiar organic solvents are ethanol and benzene.

solvents and factors affecting tHe dissolving Process People are most familiar with solutions with liquid solvents and some mistakenly state that the solute “melts” in the solvent. This is incorrect as the solute does not change phase. A solution is homogenous and the presence of the dissolved solute cannot be visually detected so, while it may appear that a solid has become liquid (thus the term melt), the solid is in fact still a solid. It has been dissolved by the liquid solvent, but it has not changed its physical phase. The quantity of solute that dissolves in a solute (its solubility) is governed by its physical composition. Dissolving is a physical phenomenon requiring interaction of the solute molecules with the solvent molecules. The most important factor governing solubility is the simple concept of “like dissolves like.” In order for a solute to dissolve in a solvent, there must be some force of attraction between the molecules. Therefore, polar solutes prefer polar solvents and non-polar solutes dissolve more readily in non-polar solvents. Given its large permanent dipole, water is an excellent solvent for polar solutes, ionic, or charged solutes. For example, the salt sodium chloride (NaCl), dissolves readily in water. This is because the O-H dipoles in the solvent interact electrostatically with the ions in the solute salt (as shown in Figure 15.1). Water dissolves salts by aligning its dipole (partial charges) with the solute ions. The hydrogen in water is partially positively charged (+) and the oxygen is partially negatively charged (-) because of the O-H dipole. These partial charges on the solvent associate with the charges on the ionic solvent (negative Cl and positive Na). Conversely, non-polar solutes, for example oils, do not dissolve readily in water and are in fact repelled, resulting in two distinct liquid layers and no solution is formed.

Figure 15.1 Water Dissolving Salt (Drawing by T. Michelle Jones-Wilson)

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163

Another important factor governing solubility is surface area. The greater the surface area available for interaction, the more readily a solute will dissolve. Since small solute particles have larger surface area in contact with the solvent, they tend to dissolve more readily than larger particles.

effects of teMPeratUre and PressUre on tHe solUBility of a solUte Under some conditions (increased pressure or altered temperature), a solute’s solubility can be temporarily exceeded. In that case the solution is considered supersaturated. Whenever any measurement is made volumetrically there is a temperature effect that must be considered. Often it is small and can be considered and discarded; however, one must be aware of temperature effects because they are not always negligible. If heat is released as a solute dissolves (an exothermic process) then an increase in temperature decreases solubility of the solute as the solubility equilibrium shifts towards the left (undissolved solute). The reverse is also true; when a solute absorbs heat as it dissolves (endothermic process), an increase in temperature favors dissolution of the solute. The effect of external pressure on solutions of condensed phases (solids and liquids) is negligible. However, in gaseous solutions (gaseous solvent or solute) pressure is critical. Henry’s law governs the solubility of gasses and states that the solubility of a gas is directly proportional (linearly related) to the pressure of the gas above the solution, (C=k*Pgas, where k is the Henry’s law constant). Low pressure decreases gas solubility whereas high pressure increases the solubility (literally pushing solute molecules closer together). Increased pressure forces more gas into solution. Pressure dependant solubility of gases in liquids is the reason for the “bends,” a condition experienced by deep-sea divers when they come to the surface too quickly. Under pressure (at depth) the concentration of gases dissolved in the blood (an aqueous solution) increase. At atmospheric pressure the concentration of gases decreases. If the diver surfaces quickly without allowing a gradual change in concentration of dissolved gases, rapid expulsion of the gas (primarily nitrogen) is exceedingly painful and can be fatal.

PHysical and cHeMical ProPerties of acids and Bases Acids and bases are commonly encountered in aqueous solutions (as shown in Table 15.2 below). Both are caustic (causing burns or corrosion) when encountered in sufficient concentration. Both are generally good conductors of electricity due to the presence of ions in solution. Acids are most commonly sour tasting. For example, vinegar has a tart sour taste; it is a dilute solution of acetic acid in water. Bases are often bitter. For example, a solution of baking soda in water (sodium bicarbonate) can be used to clean teeth although the taste is somewhat bitter. Acids

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164

can be detected easily as acidic substances turn blue litmus paper red. Conversely bases turn red litmus paper blue. Table 15.2 Common strong and weak acids.

Name

Chemical Formula Hydrochloric acid HCl Sulfuric acid H2SO4 Nitric acid HNO3 Sodium hydroxide NaOH Sodium bicarbonate NaHCO3

Strength Common Use

Ammonia

NH3

weak

Acetic acid

CH3COOH weak

Carbonic acid

H2CO3

strong strong strong strong weak

weak

Lower pH in pools and spas Lead acid storage batteries (car) Fertilizer production Oven Cleaners Baking soda--cleaning and baking Household cleaner in aqueous solution Vinegar—cleaning and food stuff Carbonated beverages

In non-protic solutions the more general Lewis definition of acids and bases as electron donors and acceptors, respectively, is employed. In protic solutions, most commonly aqueous solutions, the Bronsted-Lowry defintion is used. Bronsted-Lowry acids donate a proton, whereas bases accept a proton. PH and tHe

effects of BUffers

The concentration of acid in solution is generally expressed in units of molarity (M). For solutions of strong acids, the hydronium ion concentration in aqueous solution is equal to the acid concentration. For weak acids it is determined using the equilibrium expression and the acid equilibrium constant Ka. However, these concentrations, are generally small, even for strong acids. Using molarity (M) to express the concentrations is correct; however, it is often inconvenient given the small concentrations of hdyronium ion. In response to this a scale has been defined to provide whole number reference points for these small molar concentrations. This scale is the pH scale, and it is simply the normal logarithm (base 10) of the molar concentration of H+. The log value is then multiplied by -1 to make the scale positive, as shown below (brackets indicate concentration expressed as molarity (M)=moles solute/liter solution). The pH scale is simply the molar concentration of acid expressed logarithmically (pH = -log[H3O+]). For example for a 1.53x10-4 M concentration the pH is 3.81 (pH=-log1.53x10-4=-1*-3.81=3.81) Because H+ cannot exist freely in solution (it is tied to water) and instead exists as the hydronium ion (H3O+) there is a maximum and minimum concentra-

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165

tion of hydronium ions that can be present in water. These concentrations are determined by the equilibrium constant of water. These concentrations provide the practical upper and lower limit of the molar concentrations, while the negative log of these molarities provide the common boundaries of the pH scale. These boundaries are not absolute and concentrations exceeding those commonly expressed on the pH scale do exist. Generally the pH scale encompasses the vast majority of the hydronium ion concentrations present in the laboratory. The standard pH scale ranges from 0 to 14, corresponding to H3O+ molarities of 1 and 1 x 10-14 M, respectively. The mid point on the pH scale is 7. At pH 7.0 the concentrations of hydronium ion and hydroxide ion are equal (and equal to 1 x 10-7M) and the solution is termed neutral. When the molar concentration of hydronium ion is greater than 1 x 10-7M, the pH is lower than 7, the acid is in excess compared to base and the solution is acidic. Likewise if the hydronium ion concentration is less than 1 x 10-7 M, the pH is greater than 7, the solution is basic (as shown in Figure 15.2). The effect of taking the -log of the concentration is that smaller numbers are higher on the scale.

Figure 15.2 The pH Scale (Drawing by T. Michelle Jones-Wilson)

A buffer gets its name because it buffers or resists changes; in this case the change referred to is a change in pH. Buffers resist changing pH when acids or bases are added. Buffers are extremely important biologically. Organisms like human beings are basically aqueous systems (contained in a skin and bone container). It is critical that your pH be maintained despite the millions of reactions occurring in your body that both consume and produce hydronium ions. A buffer is actually quite simple in composition. A buffer is composed of a weak acid and its conjugate base, the product of its disassociation (often called its salt). In a good buffer there are appreciable concentrations of both the intact acid and the salt at equilibrium. This allows the reaction to respond efficiently to changes in hydronium ion concentrations. For example, consider the equation below, where HA is the acid and A- is the conjugate base (salt). + HA + H2O → → H3O + A The addition of a base pushes the equilibrium to the right by consuming or neutralizing acid, but only slightly. Likewise addition of acid pushes the equilibrium to the left but only slightly. There is enough acid and enough base to react with added acid or base to keep the equilibrium in nearly the same position. Thus, additions of acid or base to a weak acid/salt solution results in small changes in pH. Of course if you add too much base or acid you can go past the buffer region and your buffer will no longer resist changes in pH. Then the solution will behave as if it is merely water and small additions of base result in large pH changes.

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review QUestions—cHaPter 15 1. A solute composed of a salt like NaCl is dissolved in water. Which of the following terms correctly describe the solution? a. Homogeneous, organic. b. Homogeneous, aqueous. c. Heterogeneous, organic. d. Heterogeneous, aqueous. 2. Air is a mixture of gases, made up of approximately 77% N2, 21% O2, 0.9% Ar, 0.03% CO2 and other trace gases. If air was considered a solution, which statement would correctly describe the solution? a. N2 is the solvent and the other gases are solutes. b. O2 is the solvent and the other gases are solutes. c. The solution is not homogeneous throughout. d. The mixture cannot be described as a solution since gases cannot be solvents. 3. Which of the following solutes would most likely be insoluble in water? a. Ethanol (chemical formula CH3CH2OH). b. BaCl2 (an ionic compound). c. Sucrose (chemical formula C12H22O11). d. Benzene (chemical formula C6H6). 4. What conditions favor increased concentration of a solute? a. Higher temperature and increased pressure. b. Higher temperature and decreased pressure. c. Lower temperature and increased pressure. d. Lower temperature and decreased pressure. 5. The concentration of which of the following solutions would be most affected by changes in pressure? a. NaCl (aq) b. CO2 (aq) c. C12H22O11(aq) d. CH3CH2OH(aq) 6. Which of the following species is a strong acid? a. NaOH (aq) b. KOH(aq) c. HCl d. NH3

Solutions and Solubility

7. Which of the following statements concerning bases is false? a. Red litmus paper turns blue when exposed to a base. b. Strong bases do not disassociate fully in aqueous solution. c. Bases are corrosive. d. Bases are proton acceptors. 8. Calculate the pH of a 0.01 M solution of HCl. a. 12 b. 2 c. 1 d. -2 9. Which of the following pH values would be considered weakly basic? a. 1 b. 5 c. 7 d. 9 (Answer Key: 1.b, 2.a, 3.d, 4.a, 5.b, 6.c, 7.b, 8.b, 9.d)

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PART V LIFE SCIENCES

Chapter 16

THE CELL

Maria Kitchens-Kintz Prokaryotic and eUkaryotic cells The two main cell types on earth are prokaryotic and eukaryotic. Each cell type is surrounded by a plasma membrane, and contains all the necessary genetic information to build thousands of proteins for cellular life. Prokaryotic organisms such as bacteria are mostly unicellular and very small. They contain no organelles, but have specialized regions where specific cellular functions take place. They also have a cell wall made from protein-sugar molecules. Eukaryotic organisms are mostly multi-cellular in nature, are bigger than prokaryotic cells, and organize their cellular functions into organelles. The organisms that make up this cell type are fungi, some algae, plants, and animals. Plant cells have an additional cell wall made from cellulose that provides rigidity for the plant cells.

strUctUre and fUnction of PlasMa MeMBranes and organelles PlasMa MeMBranes

All cells are surrounded by a plasma membrane and additional barriers that control what is leaving or entering the cell (as shown in Figure 16.1). Plasma membranes consist of a phospholipid bi-layer. A phospholipid is made of a glycerol backbone molecule, with 2-fatty acid chains, and a phosphate group.

Cell Wall (plants & algae)

Phosphate Group

H2O

The Cell

170

Phospholipid

Fatty Acid Chains

is

os

yt

c xo

H 2O

Cell #2

E

ytosis

Endoc

CL-

Signal In

Adhesion

CL-

Signal Out

Figure 16.1 Plasma Membrane and Additional Barriers (drawing by Maria Kitchens-Kintz and Andrew Cross)

Membranes have selective permeability, meaning they will allow some substances to cross the membrane more easily than others. Some molecules such as water move freely across the bi-layer, to maintain osmotic balance. Some molecules must enter and leave the cell via the endocytosis-vesicle where the molecule is absorbed by the cell or the exocytosis-vesicle where the molecule is detached from the membrane. Within this bi-layer are numerous protein molecules that can move freely within the bi-layer. These proteins have several important functions, including the following: (a) securing cells together, as in tissues and organs, (b) processing chemical signals from the environment via hormone communication, and (c) moving molecules such as sodium and chlorine in and out of the cell.

internal organization and organelles

All cells have a semi-fluid medium inside called the cytoplasm in which the internal components are suspended. They also have a cytoskeleton, which is a network of fibers throughout the cytoplasm that gives mechanical support to the cell and helps maintain its shape. Prokaryotic cells (bacteria) contain no organelles. The internal components are organized into structured regions where cellular reactions take place. In eukaryotic cells, the internal components are compartmentalized into membrane-bound organelles that perform specific functions in the cell (as shown on Figure 16.2). Some of the major organelles and their function include the following: (a) the nucleus, which contains the DNA wrapped in proteins called chromosomes, (b) ribosomes, which are the site of translation of mRNA into proteins, (c) the rough endoplasmic reticulum (ER) with ribosomes attached, which helps maturate new proteins, (d) the smooth endoplasmic reticulum, which functions in lipid and fat synthesis and drug detoxification, (e) the golgi apparatus, which modifies and stores products of the ER for specialized secretion, (f) mitochondria,

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which is the site of cellular respiration, (g) chloroplasts, which is site of photosynthesis in plant and algae cells, and (h), vacuoles, which perform a variety of functions in cells such as water storage in plants to provide rigidity. Plasma Membrane Endoplasmic Reticulum

Cell Wall (plants & algae)

Chloroplast Site of Photosynthesis

Rough

Ribosomes

Smooth Golgi

Nucleus DNA Chromosomes

Protein Synthesis & Maturation

Vacuole

Cytoplasma & Cytoskeleton

Mitochondria Site of Krebs & ETC

Figure 16.2 Organelles (drawing by Maria Kitchens-Kintz and Andrew Cross)

cHeMical reactions in resPiration and PHotosyntHesis cellUlar resPiration

All cell types perform millions of reactions every second of the day, and need a constant and ready supply of energy. This energy is provided by adenosine triphosphate (ATP) molecules (as shown in Figure 16.3). The energy used by cells comes from the breaking of the bonds in food molecules a cell takes in (animals) or creates through sunlight (plants). This energy is then transferred and stored in CO2

Cell Wall (plants & algae)

Glucose

Fermentation

Pyruvate (Alcohol, Glycerol, etc.) ATP

Mitochondria

Electrons Glucose

Glycolysis

Pyruvate ATP

Electrons ETC

KREBS CO2

ATP

O2 + Electrons+H2

Inside Cell

H 2O

Plasma Membrane

To Lungs Gills Stomata

From Lungs Gills Stomata

Figure 16.3 Glycolysis, Fermentation, and Cellular Respiration (drawing by Maria Kitchens-Kintz and Andrew Cross)

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ATP molecules. ATP is produced in the cell via the following three processes: glycolysis, fermentation, and cellular respiration. Glycolysis (no oxygen required) takes place in the cytoplasm of the cell, and is an integral part of the cellular respiration pathway, so much so that it is commonly taught as a component of the respiration process. However, it produces ATP without the need for oxygen. In glycolysis, glucose is broken down into pyruvate molecules and stripped of electrons. Glycolysis produces only two ATP molecules, and the electrons stripped during this process are sent to the mitochondria for further processing in cellular respiration. Almost all cells have the ability to produce energy via fermentation (no oxygen required). This process can produce some ATP “cheaply” for the cell, but not enough to provide all the needs of the cell. It takes place in the cytoplasm of cells, and occurs when O2 is not available or the cell cannot provide O2 fast enough for cellular respiration. In this process glucose is broken down, producing a small amount of CO2, pyruvate, and ATP. From there the pyruvate is converted to a variety of by products, including alcohol, lactic acid, and glycerol. Cellular respiration (oxygen required) takes place in a specialized region in the cytoplasm of the prokaryotic cells. In eukaryotic cells, the site for this process is in the mitochondria. The following section will describe this process in eukaryotic cells, which includes plant cells. Cellular respiration is divided into two pathways—the KREBS Cycle and the Electron Transport Chain (ETC). In the KREBS Cycle, the pyruvate from glycolysis is transported to the mitochondria and completely stripped of electrons. This process produces CO2 waste molecules that are picked up by the blood cells and delivered to the lungs and expelled from the body through exhaling. In plants the CO2 is released through stomata in leaves and in fish it is released through the gills. All the electrons stripped from food molecules during glycolysis and the KREBS cycle move to the ETC, which is located in the inner membrane of the mitochondria. This is where most of the ATP will be generated. The electrons are passed along proteins in the inner membrane of the mitochondria, moving hydrogen ions across the inner membrane matrix against a concentration gradient. As the hydrogen ions move back through the mitochondrial membrane and back down the concentration gradient, energy is released and then captured in the bonds of ATP. After the electrons are used, they are combined with oxygen and hydrogen ions to form H2O. The oxygen is provided by the organism taking in O2 from the environment and delivered to the cells. In plants this occurs through the stomata, and in animals, this occurs through the lungs or gills. If no oxygen is available, the process of cellular respiration stops, and no ATP is generated.

PHotosyntHesis

Photosynthesis is the process of building (synthesis) glucose molecules (food) using light energy from the sun (photo), and CO2 from the air. This occurs in plants

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and algae cells and some bacteria cells. All other cells must obtain their food from existing organisms. This process takes place in the cell in chloroplast organelles. There are two main components—light reactions and the Calvin Cycle (as shown in Figure 16.4).

Cell Wall Chloroplast Calvin Cycle

Light Reactons Electrons Chlorophyll Electrons H2O

H+ O2

Inside Cell

ATP

ETC

CO2

O2 + Electrons + H2+

Glucose

H 2O

Store in Cells

Glycolysis & Cellular Respiration

Plasma Membrane

Figure 16.4 Light Reactions and the Calvin Cycle (drawing by Maria KitchensKintz and Andrew Cross)

In the light reactions, sunlight activates electrons in pigments found in the thylakoid stacks in chloroplasts. Chlorophyll (green) a and b are the main pigments found in plants. Other pigments include B-carotene (orange), xanthophyll (yellow). The excited electrons are transferred to an (ETC) in the inner membrane of the stacks that produces ATP in the same manner as the ETC in cellular respiration in the mitochondria. Water is taken in by the cell, and is split by the sunlight, releasing O2 and electrons which replace the ones lost by the chlorophyll pigment. The O2 is released by the cells into the atmosphere where plants, algae and all other cells take this in for cellular respiration. The ATP is then sent to the Calvin Cycle in the stroma of the chloroplasts During the Calvin Cycle, plants take in CO2 (by-product of cellular respiration) from the environment via the stomata, and transport it to the stroma of the chloroplasts. Multiple enzymes in this cycle create glucose from the CO2, using energy from the ATP and the electrons created during the light reactions. The glucose molecules are then used and stored by plants for cellular respiration which can produce vast amounts of ATP.

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tHe cell cycle: interPHase, Mitosis, Meiosis, and cytokinesis The cell cycle is an orderly sequence of events that extends from the time a cell is first formed from a dividing parent cell to its own division into daughter cells. Cell division plays important roles in the lives of organisms because it is a process that replaces damaged or lost cells, permits growth, and allows for reproduction. The cell cycle consists of the following four distinct phases: (a) interphase, (b) mitosis/meiosis, and (c) cytokinesis (as shown in Figure 16.5).

interPHase:

Most of the cell cycle is spent in interphase. During interphase, a cell performs its normal functions and grows in size, called the G1 sub-phase. In the S-sub-phase, the cell doubles everything in its cytoplasm, and replicates the DNA/ chromosomes. In the G2 sub-phase, the cell prepares for mitosis/meiosis. Interphase can last from just a few minutes to years, depending on the cell type. When the cell replicates the DNA/chromosomes during S sub-phase, the two identical copies are con-joined to each other via the centromere. The con-joined chromosomes are called sister chromatids.

Mitosis:

Mitosis involves division of a cell into two identical daughter cells. It is an important process used for asexual reproduction of whole organisms (yeast, bacteria, some plants and animals) and for growth and maintenance (replacement of cells) in multi-cellular organisms. The mitotic phase consists of four sub-phases (as shown in Figure 16.5). In prophase con-joined sister chromatids coil and condense, and spindles generated by the centrosomes attach to the centromeres holding the sister chromatids together. In metaphase, con-joined sister chromatids line up on the equator of the cell in a tandem (head to tail) array guided by the spindle. In anaphase spindles pull the con-joined sister chromatids apart towards the poles of the cell, as each sister chromatid becomes a full-fledged chromosome of its own. In telophase the cleavage furrow begins to appear between the poles of the cell. Interphase

Mitosis 2N

G1-S-G2 Cytokinesis 2N Prophase 2N

Metaphase Spindles

Anaphase

Telophase

Figure 16.5 Mitosis (drawing by Maria Kitchens-Kintz and Andrew Cross)

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Meiosis

All multi-cellular organisms will reproduce via sexual reproduction at some point in their life cycle. Sexual reproduction occurs when a haploid sperm cell fuses with a haploid egg cell during fertilization to form a diploid zygote cell. These haploid mature sex cells are formed from diploid pre-sex cells via the process of Meiosis. Meiosis is a division process similar to mitosis, except that meiosis results in four daughter cells, rather than two, and each of the four daughter cells has half as many chromosomes as the parent cell. Meiosis occurs in two cycles called Meiosis I and II (as shown in Figure 16.6). In meiosis I, the con-joined sister chromatids are partitioned into two new cells. In meiosis II, the con-joined sister chromatids in each of the two new cells are pulled apart into individual chromosomes creating two more new cells. This process ends up with four new cells, each one having only one set of chromosomes (haploid) from the diploid pairs. When fertilization takes place between two haploid sex cells, the resulting diploid zygote now contains pairs of homologous chromosomes, and an offspring is formed Meiosis I & Cytokinesis

Meiosis II & Cytokinesis

In 2N In

Spindles

In Spindle

In

Figure 16.6 Meiosis (drawing by Maria Kitchens-Kintz and Andrew Cross)

Mistakes during meiosis can result in genetic abnormalities that range from mild to fatal. The most common abnormality is non-disjunction. In this process, the sister chromatids fail to separate correctly, producing mature sex cells with an incorrect number of chromosomes. Non-disjunction can occur during meiosis I or II. If non-disjunction occurs in an egg cell, and a normal sperm fertilizes it, the result is a zygote with an abnormal number of chromosomes. If it comes to full term, this can have devastating effects, possibly resulting in death to the new organism.

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For example, Down Syndrome, also called trisomy 21, is a condition in which an individual has three chromosome 21’s, due to a non-disjunction event during meiosis in the pre-egg cell. Chromosome 21 did not partition correctly into the new mature egg cells and so one mature egg cell ended up being diploid for 21. If fertilization takes place in this egg cell with a sperm (carrying its own chromosome 21), the resulting zygote/offspring will have three chromosome 21’s. It will be triploid for 21, and this causes a multitude of debilitating conditions in the offspring, or even death to the new organism. This condition affects about one out of every 700 children.

cytokinesis

This is the last event in cell division and it follows mitosis and meiosis. Cytokinesis is a fast event that divides the cytoplasm in half and “pinches” the parent cell into two new daughter cells along the cleavage furrow. If mitosis/meiosis occurred correctly, then the two new daughter cells should contain identical genetic material such as sodium and chlorine.

The Cell

review QUestions—cHaPter 16 1. The cell cycle is composed of all of the following except a. Interphase. b. Mitosis phase. c. Quiescence phase. d. Cytokinesis. 2. Eukaryotic cells are enclosed in what type of membrane? a. Nucleic acid helix. b. Steroidal mono-layer. c. Phospholipid bi-layer. d. Carbohydrate bi-layer. 3. The function of eukaryotic membranes is a. to control the replication of the cell. b. to control what enters the cell. c. to make proteins from the DNA. d. to produce energy for the cell. 4. The Mitochondria carry out the process of a. protein modification. b. aerobic respiration. c. photosynthesis. d. moving genetic material around the cell. 5. Cellular respiration converts energy stored in chemical bonds a. to energy used by sunlight. b. to sunlight used by plants. c. to energy used by cells. d. to energy used in photosynthesis. 6. Photosynthesis removes CO2 from the air and turns it into a. water. b. sugar (food). c. fats. d. lipids. 7. Chloroplasts are structures in plants that allow them to a. carry out respiration. b. carry out glycolysis. c. carry out photosynthesis. d. produce pyruvic acid.

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8. Homologous chromosomes a. are identical and carry the same genes. b. do not have the same genes. c. are the same between species. d. are different between species. 9. During metaphase of mitosis, the chromosomes are aligned a. at the poles of the cell. b. with the anaphase chromosomes. c. on the equator of the cell. d. none of the above. 10. In a Monohybrid cross, the offspring of an F1 generation a. will lose the phenotype of the recessive allele temporarily. b. will have the recessive allele reappear when mated to each other. c. will lose the recessive allele forever. d. both a and b (Answer Key: 1.c, 2.a, 3.b, 4.b, 5.c, 6.a, 7.b, 8.a, 9.c, 10.d)

Chapter 17

DNA STRUCTURE Maria Kitchens-Kintz

DNA is composed of bonded deoxynucleotides in a double strand configuration (as shown in Figure 17.1). Each nucleotide in one of the strands consists of a deoxy-ribose sugar (no oxygen on carbon 2), a nitrogenous base, and a phosphate group(s). There are four specific nitrogenous bases that are found in DNA; adenine (A), and Guanine (G), cytosine (C), and thymine (T). The nucleotides can also exist in the cell in three different phosphate configurations—mono, di, and tri. The DNA molecule is composed of these nucleotides linked together in a “double stranded” form. The nucleotides in each strand of the DNA molecule are connected to each other via a phosphodiester bond between the 5-carbon of one nucleotide and the 3-carbon of the following nucleotide. This structure makes the strand polar, and gives it a “strand orientation.” The two strands in the DNA molecule are held via hydrogen bonds between the different bases on each of the nucleotides in the strands. The base pairing rules, also known as the Chargaff rules, are as follows: A binds to T, G binds to C. In addition to the base-pairing rules, the orientation for the two strands must be opposite from each other. It is important to note that DNA is located inside the cell and it does not exist as a “naked” molecule; rather, it is extensively folded and wrapped around special proteins, forming the chromosomes The main function of the DNA is to store the information necessary for the cell to build new proteins. This information is transferred to the cellular machinery via the processes of transcription and translation. In addition, the DNA must be passed on to daughter cells without any changes in the sequence to avoid the production of mutant proteins that could damage the cell.

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Thymine

Adenine 5’ end O

O

O P

O

3’ end

O O O O

O

P O

O

O

O

O

Phosphate - P Deoxyribose Backbone

O P

O O O

O

P O

O

O P

O

O

O

O O O

O

P O

O

O P

O

O

O O

O

3’ end

Cytosine Guanine

O P

O

O

5’ end

Figure 17.1 The binding of nucleotides in the strands and between the strands in a DNA molecule. Note that the two strands are in opposite orientation of each other. (drawing by Andrew Cross)

dna rePlication When the cell replicates by mitosis or meiosis, it must be able to provide a full complement of DNA to each of the resulting daughter cells. The DNA must be replicated faithfully during the cell cycle before mitosis or meiosis takes place. Any change in the sequence of the DNA during replication can result in a cell that makes non-functioning proteins, and damage the cell and/or organism. DNA replication takes place during the S-phase of the cell cycle. The type of replication is known as semi-conservative, due to the fact that after replication, the two exact copies of the DNA molecules will have one newly replicated strand and one original, or “old,” strand. Replication begins at specific sequences in the DNA molecule called “origins of replication” or Ori. This section will describe eukaryotic replication, but this process can be applied to the other cell types as well. Following are the steps in DNA replication (as shown in Figure 17.2). 1. The DNA strands in the molecule separate from each other via an enzyme called Helicase, by breaking the hydrogen bonds between the nitrogenous bases. 2. Another protein, usually referred to as primase, then binds to the Ori sequence and adds short strands of RNA nucleotides to each of the “old” strands. These short sequences are known as primers, because they “prime” the old strands for replication.

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3. An enzyme called DNA Polymerase binds to the two strands at the primer locations and begins to add new DNA nucleotides to form a new second strand. The polymerase constructs the new strand by forming phosphodiester bonds between the incoming new nucleotides, and hydrogen bonds between the nitrogenous bases of the old and new strands. 4. When replication is finished, another type of DNA polymerase binds to the RNA primers on both strands, excises the RNA nucleotides, and replaces them with DNA nucleotides. 5. A phosphodiester gap in the new strands is left after this excision process. A protein called ligase then binds to this gap and forms the phosphodiester bond, “sealing” the nucleotides in the new strand.

Figure 17.2 Schematic of DNA replication. Note that replication is proceeding in the opposite direction from the Ori Sequence. (drawing by Andrew Cross)

transcriPtion Transcription is a process that involves proteins and genes. Proteins are composed of amino acid molecules linked together in a highly specified order. There are 20+ amino acids used in protein composition. They have very diverse functions, from forming structures like our skin and hair, to acting as enzymes that facilitate the millions of biochemical reactions in cells. Proteins are constantly being replaced by the cells, and have to be made via a cellular machinery that involves another type of nucleotide molecule called RNA. It is from the RNA that the cellular machinery directly obtains the information for the specified order of amino acids for a particular protein. The RNA molecule is a copy of a stretch of nucleotides within the DNA molecule called a gene. A DNA molecule is composed of millions of nucleotide base pairs. Along this DNA molecule, some of the base pairs form what are known as genes. The “gene”

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portion of the DNA is responsible for producing a single stranded copy of the base pair sequence using RNA nucleotides. This process is known as transcription. There are three types of genes—those that produce transfer RNA copies (tRNA), those that produce ribosomal RNA (rRNA) copies, and those that produce messenger RNA (mRNA) copies. Within the gene, the sequences of the base pairs are arranged in specific regions: promoter and transcribed regions. Following are the steps in transcription (as shown in Figure 17.3). 1. An RNA polymerase protein binds to the promoter sequence of the gene. 2. The RNA polymerase breaks the hydrogen bonds in the DNA double helix. 3. The RNA polymerase then begins to move along the DNA molecule to create a copy of only one of the DNA strands using ribonucleotides. 4. The RNA polymerase will continue down the DNA molecule in this manner until it comes to a transcription termination sequence in the gene that dislocates it, and the new RNA copy from the DNA molecule. RNAP Coding Strand

5’ 3’

Template Strand

Gene

Coding Strand

5’ 3’

RNAP Template Strand

5’

3’ 5’

3’ 5’

3’ 5’

RNAP

5’ 3’

Coding Strand Template Strand

3’ 5’

Figure 17.3 Transcription of a gene in the DNA. One strand in the gene of DNA is copied using ribonucleotides. (drawing by Andrew Cross)

translation After transcription, the RNA’s are moved out of the nucleus and used in the process of translation. This process happens outside the nucleus in the cytoplasm, and on the rough endoplasmic reticulum. However, before the RNA’s can be used in translation, they are first processed. Following are the steps in RNA processing. 1. tRNA- this RNA copy will be folded such that it will expose three bases that make up what is known as the anti-codon sequence. It will also have bonded to it an amino acid. The type of amino acid that is bound depends on the sequence of the anti-codon.

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2. rRNA- this RNA copy will be cut into smaller segments, and then combined with other proteins in the cell to form the ribosomes. 3. mRNA- this RNA copy contains the codons. Prokaryotic cells do not modify their mRNA extensively, and are immediately used in translation to a new protein. Eukaryotic cells place a poly-AAAAAAAAA segment (or tail) of RNA on one end and splice out segments of the mRNA called introns Then they combine the remaining segments (called exons) to form a mature mRNA molecule. At this point, the RNA’s are ready to be used to build new proteins for the cell in a process called translation. Following are the steps in translation (as shown in Figure 17.4). 1. The ribosomes bind to the mRNA, and holds it in place for the tRNA’s to come in and bind to the codons within the translation region. 2. The first codon that the ribosomes will search for on all mRNA’s is AUG. The tRNA that will bind to this codon has the anti-codon of UAC, and will always have bound to it the amino acid Methionine. Therefore all proteins begin with methionine amino acid. 3. The ribosomes then allow a second tRNA molecule to bind to the second codon in the mRNA. As mentioned before, the anti-codon of this tRNA will depend on the codon sequence in the mRNA. 4. When the two tRNA’s are base-bonded to the mRNA, the methionine from the first one will be transferred and bonded to the amino acid on the second tRNA via a peptide bond. 5. This will continue with subsequent codons along the mRNA until a stop translation sequence is reached on the mRNA. At that point, the ribosomes and new protein come off the mRNA.

DNA

mRNA Transcription

Mature mRNA

Nucleus

Transport to cytoplasm for protein synthesis (translation) mRNA

Cell Membrane

Figure 17.4 Translation of mRNA using ribosomes and tRNA's bounded to amino acids. (drawing by Andrew Cross)

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caUses and resUlts of MUtations Mutations in the sequence of the DNA result from a change in a nucleotide or a pair of nucleotides in the DNA molecule. These changes can occur for several reasons, including a mistake in DNA replication by the DNA polymerase, exposure to the sun, and exposure to mutagenic chemicals found in pesticides and processed foods. If the mutation occurs in a gene, it can cause a change in the transcription sequence of the DNA within the gene, and therefore how the cell will translate the RNA copy. This can potentially destroy the function of the protein, or change how it functions in the cell; therefore, almost all mutations that occur in genes are detrimental to the cell, and almost always result in the death of the organism.

interaction Between inHeritance and environMent The majority of mutations occur in somatic cells (non-sperm and egg cells), and are not passed on to the next generation. If they do occur in the sperm and egg cells, then the ensuing generations will inherit this change. If the mutation in the gene results in an amino acid change in the protein that is beneficial, and it occurs in the reproductive cells, the mutation will become the “normal” over time as it is passed down from generation to generation. Offspring that inherit the mutation also thrive better than their counterparts, and reproduce more. This process, called natural selection, allows the beneficial mutation to proliferate within the population and after many generations, it becomes the new “normal” for the species.

Mendelian inHeritance In the mid 1800’s, Gregor Mendel studied how traits were passed on from one generation to another by studying the color traits of the flowers on pea plants. These “traits” are now known to be effected by “genes” in the DNA molecule. Most genes can produce different versions of proteins, and are called alleles. Remember that in the cell there are homologous (same) pairs of DNA chromosomes and each one shares the same genes. However, within an individual’s genome, there can be two alleles of the same gene on the homologous pairs. An example is the eye-color gene in people. Let’s say that one chromosome in the homologous pair has the blue eye-color allele, and the other chromosome has the brown eye-color allele. This is known as being heterozygous for the two alleles. If the individual has inherited two alleles that are the same such as the blue/ blue alleles, this person is said to be homozygous for the blue allele, and so forth. Interestingly, only the brown color (phenotype) will be observed in the individual that is heterozygous blue/brown. This is because the brown allele is dominant over the blue allele which is considered recessive. An individual must inherit two recessive alleles (homozygous) in order for the phenotype to be observed.

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During meiosis, the replicated DNA is distributed to four daughter cells, each one having half the compliment of the genome (1N) or one allele of the gene per cell. When fertilization takes place between individuals, the phenotype of the offspring is set by the expression of the genotypes (2N) inherited, and the dominant/ recessive status of the different alleles of the genes. Let’s use this model to predict the genotypes, and therefore phenotypes, of the color of corn kernels. Each kernel on a cob of corn is the result of a fertilization event between a mature egg and sperm cell creating an offspring. Tracking only one trait is known as a monohybrid cross. The gene that produces the kernel color has two alleles—purple-C (dominant) and yellow-c (recessive). Dominant alleles are always referred to with a capitol letter, and the recessive allele with a lowercase letter. Each letter represents a homologous chromosome with that gene-allele type in the DNA sequence. If two corn plants with the genotype CC (2N, phenotype-purple) and cc (2N, phenotype-yellow) are mated, the resulting offspring will all be purple in color. Let’s see how this happens, by referring to the table below. Parent 1(2N)

Homologous chromsomes DNA replication

Parent 2(2N)

CC-purple

X

cc-yellow

CC,CC

cc,cc

After meiosis:

C

c

four mature

C

c

sex cells with

C

c

genotypes of (1N)

C

Random Mating

c

Figure 17.5 Mendelian Inheritance (drawing by Maria Kitchens-Kintz)

After random mating, all off-spring will have the genotype of C/c and a phenotype of purple. This is known as the F1 generation. The yellow phenotype is missing in this generation due to the dominance of the purple allele. A punnett square is used to observe the potential genotype/phenotype of the offspring. In this square, the parent sex cell (1N) genotypes are placed along the top and side of the square, then each one is mated, and the genotype/phenotype of the offspring are placed in the ensuing boxes (as shown in Table 17.1). Table 17.1 Punnett square for genotype/phenotype prediction of offspring from a Monohybrid cross between parents with genotype/phenotype or purple- CC and yellow-cc. 100% of offspring are purple.

Parents c

C Cc Purple

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Let’s mate the F1 generation using the punnett square. The genotypes of the parents egg and sperm cells are both C and c. When the sex cells are randomly mated, ½ of the offspring will have the genotype of C/c and ¼ C/C, all with a phenotype of purple. The other ¼ of the offspring will have the genotype of c/c and have the phenotype of yellow (as shown in Table 16.2). This is the F2 generation, and the yellow phenotype has reappeared. This gives a ratio of 3:1 purple to yellow kernels Table 17.2 Punnett square for genotype/phenotype prediction of offspring from a Monohybrid cross between F1 parents with genotype/phenotype or purple- Cc.

F1 parents C c

C CC Purple cC Purple

c Cc Purple cc yellow

Frequently, more than one trait is studied in genetics and consequently the analysis becomes very complicated. However, the punnett square is still used to predict the ratio of the genotype/phenotype of the offspring. Let’s look at two traits in corn kernels: color- purple (C), yellow (c) and texture-smooth (T), wrinkled (t). This is known as a di-hybrid cross. The Parent generation has the genotypes of CCTT, purple/smooth, and cctt yellow/wrinkled. Determine the the genotypes of the sperm and egg cells in the square (CT or ct), and use a punnett square to randomly mate them. All of the offspring in the F1 generation will have the genotype of CTct, and all will be purple/smooth. Both recessive traits, yellow/wrinkled will not be visible. Let’s mate the F1 generation. The genotypes of the sex cells for both parents will be CT, ct, Ct, and cT. After random mating of the sex cells, the F2 offspring will have the genotype combinations of CCTT, CcTT, CCTt, CCtt, Cctt, ccTT, ccTt, cctt. The phenotype ratio will be 9- purple/smooth, 3-purple/wrinkled, 3-yellow/smooth, and 1- yellow/wrinkled, which is a 9:3:3:1 ratio (as shown in Table 17.3).

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Table 17.3 Punnett square for genotype/phenotype prediction of offspring from a Dihybrid cross between F1 parents with genotype/phenotype of CTct/purple, smooth.

ct

CT

cT

Ct

CT CTct Purple Smooth CTCT Purple Smooth CTct Purple Smooth CTCt Purple Smooth

ct ctct yellow wrinkled CTct Purple Smooth cTct yellow Smooth Ctct Purple wrinkled

Ct Ctct Purple wrinkled CTCt Purple Smooth cTCt Purple Smooth CtCt Purple wrinkled

cT cTct Yellow smooth CTcT Purple Smooth cTcT yellow Smooth CtcT Purple Smooth

non-Mendelian inHeritance The above genes and their alleles are following what is known as classic Mendelian genetics. Some genes and their alleles do not strictly follow these rules. This can be due to incomplete dominance or co-dominance of an allele, or two genes that are closely linked such that they will not segregate independently of each other during meiosis. In incomplete dominance, there is an intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele. This results in a combined phenotype. In co-dominance, the alleles are expressed equally. An example of this is the blood type gene. If a person inherits both an A and B allele of the blood type gene, both of the alleles will be observed in the individual. Hence the different blood types of AA or just A, BB or just B, and AB called type AB.

recoMBinant dna In this process, portions of DNA from one organism is “cut out” and then “pasted” into the genome of another organism, creating a unique organism. The cutting of the DNA is accomplished via proteins called restriction enzymes (RE). These proteins were discovered in bacteria and will cut the DNA at specified sequences. When a RE cuts the DNA, they break both the phosphodiester bond in the strands and the hydrogen bonds between the bases. These proteins also cut the DNA such that they can leave two types of ends—blunt and sticky.

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B l u n t 5’----CCCGGG----3’ RE 5’----CCC-3’OH’-end3’----GGGCCC----5’ CUT 3’----GGG-5’P Sticky end-

5’ ----GAATTC----3’ RE 3’----CTTAAG----5’

5’----G-3’

OH

P-5’-GGG----3’ OH 3’-CCC----5’ P

CUT 3’----CTTAAG-5’P

5’-AATTC----3’ OH

3’-G----5’

In sticky ends, there are bases that are not bonded to their complement bases. They have a great tendency to anneal back together, or to another piece of DNA with the same sticky ends. The two newly cut pieces of DNA are then bonded (pasted) together via a phosphodiester bond with protein called ligase (as shown in Figure 17.6). DNA

Organism 1

RsaI

RsaI

Cut DNA

Organism 2 DNA RsaI

Discard Combine and ligate DNA strands with ligase enzyme. New genome

Figure 17.6 Translation of mRNA using ribosomes and tRNA's bounded to amino acids. (drawing by Andrew Cross)

Once the two DNA pieces are pasted together with ligase, the new DNA is placed into a host cell for expression of the DNA. This process is known as transformation in bacterial cells and transfection in eukaryotic cells. This type of work is being done to produce human insulin in bacterial cells, silk in goat milk, or in gene therapy to replace or repair genes that cause human diseases or conditions.

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review QUestions—cHaPter 17 1. The main purpose of DNA is to provide which of the following? a. A storage mechanism for information used in the development of new proteins. b. A protective layer for chromosomes. c. A medium for transmitting neural impulses. d. A buffer to protect cells against toxins. 2. Which of the following occurs as a result of DNA replication? a. New cells which are different from the original cells are produced. b. A protective coating for the cell is developed. c. Exact copies of the DNA molecule are constructed. d. The process of enzyme absorption occurs. 3. Transcription is a process in which a. a new gene (RNA molecule) is produced. b. proteins are replaced. c. the nucleus of a cell divides. d. RNA is converted to DNA. 4. During translation RNA’s are used to a. inhibit cell growth. b. build new proteins. c. remove toxins from the cells. d. accelerate cell division. 5. Mutations are almost always __________ and occur when there is a change in a __________. a. helpful, nucleotide b. helpful, cell wall c. harmful, nucleotide d. harmful, cell wall 6. Which of the following may cause a mutation to occur? a. A mistake in DNA replication. b. Exposure to the sun. c. Chemicals found in pesticides and processed foods. d. All of the above.

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7. Being heterozygous describes which one of the following scenarios? a. One chromosome has the blue eye-color allele and the other chromosome has the brown eye-color allele. b. Both chromosomes have the blue eye-color allele. c. Both chromosomes have the brown eye-color allele. d. All of the above. 8. The blood type gene is an example of which of the following processes? a. Mendelian Inheritance. b. DNA Replication. c. Translation. d. Non-Mendelian Inheritance. 9. Natural selection is a. a process where offspring inherit the mutation and thrive better than their counterparts and reproduce more. b. a process where the RNA’s are moved out of the nucleus. c. a process that involves proteins and genes. d. a process that involves genetic engineering. 10. In which of the following processes are portions of DNA from one organism cut out and pasted into the genome of another organism, creating a unique organism? a. Translation. b. Transcription. c. DNA Replication. d. Recombinant DNA. (Answer Key: 1.a, 2.c, 3.a, 4.b, 5.c, 6.d, 7.a, 8. d, 9.a, 10. d)

Chapter 18

DIVERSITY OF LIFE Cindi Smith-Walters

cHaracteristics of life and Biological levels of organization cHaracteristics of life

What do we mean when we say something is alive? What are the differences between biotic (living) and abiotic (non-living) things? Be warned, many people have different opinions of what living means, and sometimes nonliving things can resemble living things. An automobile for example, uses (eats) gasoline and creates waste (exhaust). To limit this confusion, there are a number of characteristics of life which scientists typically agree living things must display. All of the following must be true for an organism to be considered living. 1. Composed of cells: According to the Cell Theory, all living things are made of cells. Some organisms are single-celled, like bacteria, or multi-celled, like humans. All living things begin as a single cell. In multi-celled organisms the cell divides and multiplies and sometimes differentiates into specific cells types such as skin, heart, and muscle. and each has a defined job. These cells then work together for the good of the organism. Cells perform the processes listed below. 2. Require/use energy: Living things require energy, usually in the form of ATP (Adenosine Tri-phosphate) and use this energy to carry out activities such as locomotion, reproduction, or metabolism. Some organisms (producers) are able to take sunlight energy or chemicals from their environment and change them into usable energy through photosynthesis or chemosynthesis respectively. Other organisms (consumers) must eat producers or other consumers to receive the energy that has been stored in their bodies.

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3. Reproduce & display heredity: This occurs via asexual (one parent) or sexual (gametes from typically two parents) means to pass their traits on to offspring. Asexual methods include cuttings from plants (vegetative propagation), budding (as in yeast cells), and cellular fission (single celled organisms splitting into two). Sexual methods include egg and sperm (as in vertebrates), conjugation (single celled organisms exchanging cellular contents), and pollination (movement of plant pollen from stamen to pistil). 4. Respond to stimuli: Living things react to forces beyond their control and adjust to both internal and external environments. Plants turn toward the sun, we squint in bright light, our pulse may race at a scary movie, and our bodies let us know when we are hungry or thirsty. 5. Grow, age, and display a life span: Growth is an increase in cell size and, in multi-celled organisms, it is also an increase in cell numbers. As humans grow older they also increase in size/cell number. They also age (get older), and will eventually die. 6. Maintain homeostasis: Through homeostasis living things maintain a state of internal balance. They are able to regulate internal chemical processes precisely and maintain a stable internal environment. Examples in humans include maintaining body temperature, glucose levels in the bloodstream, regulation of water or minerals in the body, and blood pressure.

Biological levels of organization

Cells are the basic unit of structure of living things. Groups of cells with similar structure and function working together to perform a specific activity are called tissues. Groups of tissues that work together to perform a specific activity are called organs. Groups of organs that work together to perform a specific function for an organism make up an organ system. Lastly, groups of organ systems make up the individual organism. Thus the biological levels of organization are from simple to complex: cells → tissues → organs → organ systems → organism. An example would be heart cells → cardiac tissue → the heart → the circulatory system → you!

tHe HierarcHical classification scHeMe Taxonomists, scientist who study, classify, and name organisms, have identified around 2 million species of organisms on Earth and estimates say there are probably more than 10 million species, meaning we have classified only a fraction of them. Classifying organisms by grouping them makes the study of life easier. Think of shopping in a department store. Specific products are found in the different departments—shoes, cosmetics, linens. Within the specific department you will find products grouped together. In the shoe department for example athletic shoes are together, dress shoes in another, and boots in still another. Using a sys-

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tem based on similarities enables scientist to more easily identify a particular organism within the crowd of two million. Living things are classified into groups which run from general (Domain) to very specific (Species). In order, these hierarchical ranks are Domain, Kingdom (Division), Phylum, Class, Order, Family, Genus, Species. A grouping as large as Domain is all inclusive and therefore not precise. Each level that follows becomes increasingly more specific until we define a definite explicit organism (species). A number of mnemonic devices may help one to remember the levels of classification in order from most inclusive to least inclusive. Examples are found in Table 18.1. Table 18.1 Three common mnemonic devices to remember the levels of classification from most inclusive to least inclusive. Most Inclusive

Least Inclusive

Domain

Kingdom

Phylum

Class

Order

Family

Genus

Species

Do

kings

play

chess

on

fine

green

silk

Did

Kathy

put

candy

on

Father’s

good

suit

Did

King

Philip

come

over

for

great

spaghetti

These groupings form the most common scheme for classifying organisms, although other groupings and categories are also used. For example, consider domesticated dogs. Dobermans and dachshunds both carry the same genus and species name, Canis familiaris, but belong to different sub-species that we refer to as breeds or varieties. These organisms vary slightly from other individuals of the same species, but not enough to be considered a separate species. Table 18.2 gives the classification scheme for the European wolf. Using binomial nomenclature such as Canis familiaris reduces the confusion of using only common names. For example, Cambrellus puer is known by a number of ordinary names, including crayfish, crawfish, crawdad, and even mudbug! Two people could be talking about the same organism and not know if they are using different common names for the same species. Table 18.2 Classification Scheme for the European Wolf

Domain

Eukarya

Kingdom

Animal

Phylum - Division is used for plants

Chordate

Complex cells which contain a nucleus and organelles Multicellular organism; a consumer but does not digest food externally; cannot make its own food Had a notochord that developed into spinal cord encased within a backbone

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Class

Mammal

Order Family

Carnivore Canid

Genus Species

Canis* lupus*

Has hair, bears live young, nurses young with mammary glands Prefers to eat meat Has non-retractable claws, a long muzzle, separate toes Member of the dog family A particular type of wolf, the European Wolf

* Genera are written with an upper case 1st letter & species with a lower case 1st letter. To be correct, scientific names should be written in italics when in print or underlined when written in longhand. Examples: common cat = Felis domesticus, humans = Homo sapiens, red maple = Acer rubrum

cHaracteristics of virUses, arcHaeaBacteria, eUBacteria, Protists, fUngi, Plants, and aniMals virUses

Viruses are not considered living because they are not made of cells, the building blocks of life. They are simply genetic information (RNA or DNA) surrounded by a protein coat. Viruses are extremely tiny particles, smaller than the smallest cell. They lack the enzymes and the cellular machinery necessary for carrying out life processes so reproduction is their only function. To reproduce they must come in contact with the correct type of host cell, lose their protein coat, and take over the cell’s nucleus, forcing it to combine its genes with viral genetic information and make more of the virus. Viruses are difficult to eradicate because we have not found a way to render them inactive without killing the host cell. Viruses are notorious for their disease-producing potential. In humans viruses cause such diseases as measles, colds, rabies, chicken pox, yellow fever, the flu, AIDS, fever blisters, and venereal herpes. It is believed that some cancers have their origin with a viral introduction. Viruses can also cause plant disease such as tobacco mosaic, rice dwarf, and Dutch elm disease.

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Table 18.3 The Six Kingdom Classification Model

Kingdom

Characteristics

Examples

Archaebacteria (Ancient Bacteria)

Prokaryotic cells with no nucleus or membrane bound organelles, all chemosynthetic producers (autotrophs), found in WILD habitats where no oxygen is found, circular DNA

Thermophiles, Methanogens, Halophiles

Eubacteria (Simple Bacteria)

Prokaryotic cells with no nucleus or membrane bound organelles; some are decomposers (special heterotrophs), some photosynthetic producers, found in relatively MILD habitats where oxygen is found, some are classified by their shapes (rod, spiral, sphere), wide-ranging on Earth, contains both helpful and disease causing bacteria, circular DNA

E. coli, Streptococcus, Acidophilus

Protista

Eukaryotic cells; most single celled, few like algae are multicelled, some fungi-like (absorptive decomposers), some are plant-like (photosynthetic producers/autotrophs), some are animal-like (ingestive heterotrophs); ‘junk drawer’ kingdom

Slime Mold, Algae, Amoeba, Paramecium,

Fungi

Eukaryotic cells; digest food externally then absorb it (absorptive heterotrophs), differ from plants in composition of cell wall, methods of reproduction, body structure; ‘soup eaters’

Yeast, Bread Mold, Mushrooms

Plant

Eukaryotic cells; all are multicellular photosynthetic producers/autotrophs containing chloroplasts and all plant cells contain made cellulose

Mosses, Ferns, Grasses, Conifers, Trees, Flowers

Eukaryot

Eukaryot

Eukaryot

Eubacteria*

Archeae*

Domain

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Eukaryot

Domain

Kingdom

Characteristics

Examples

Animal

Eukaryotic cells; all are multicellular ingestive heterotrophs, most move and except for the very simple species reproduce by means of egg and sperm cells. Divided into invertebrates and vertebrates (with a backbone). Vertebrates divided into those that are cold-blooded and those that are warm-blooded

Sponges, Coral, Worms, Insects, Crabs, Fish, Birds, Amphibians, Reptiles, Dogs, Humans,

* In older references these kingdoms are grouped together as Kingdom Monera. This five kingdom model has been standard since the late 1960’s. The current classification model however, exhibits six kingdoms.

arcHaeaBacteria and eUBacteria

Both Archaeabacteria and Eubacteria are single-celled organisms and are prokaryotic, meaning before nucleus (See Table 18.3). Prokaryotes differ from the cells of more advanced organisms (eukaryotes) because prokaryotes have no nucleus; rather, their genetic information floats freely in the cytoplasm of the cell. In addition, they do not have the membrane bound organelles like eukaryotes display. Prokaryotes reproduce by an asexual process in which the parent cell simply divides into two daughter cells. Prokaryotic cells are small in size, ranging from 0.5 to 10 micrometers (the average eukaryotic cell is much larger), and some may be able to move on their own by means of a stiff, rod-like flagellum. Archaebacteria are classified into several groups but all are found in harsh locations such as boiling water, thermal vents, stagnant marsh water, under conditions of no oxygen, or in highly salty or acidic environments. This ability to live in these extreme environments leads to the descriptive name of extremophiles. Because the majority are chemosynthetic, Archaebacteria differ from all other organisms on Earth so taxonomists place them in a kingdom of their own. Eubacteria are the true or simple bacteria and they are the type most of us are familiar with. As opposed to archaebacteria. They live in mild habitats under much less harsh conditions. We identify them by shape: the rod shaped (bacilli), the round (cocci), and spiral shape (spirilla). Many eubacteria are decomposers and get their nutrition from dead organic materials. Some are autotrophic and make their own food through photosynthesis. Some eubacteria are pathogenic (cause disease) but many are helpful to humans and the environment in general. Helpful eubacteria include those that are nitrogen-fixers in the soil, those that break down and recycle nutrients so that they may be used again by plants, and still others that are mutually symbiotic by living within the guts of termites, cows, or even humans and aiding food digestion.

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Bacteria are also used to ripen cheese and yogurt, improve the flavors of certain foods, ferment silages used for cattle feed, and to produce some antibiotics and even vitamins.

Protists

In contrast to the prokaryotic cells that make up Archaebacteria and and Eubacteria, the cells of Protists are eukaryotic, because they contain nuclei and membrane-bound organelles. Many are single-celled with one or more nuclei, although some are organized into cell colonies. Protists include fungi-like, plant-like and animal-like members. The fungilike include the slime-molds who, grow in moist places, absorb their food from organic material, and form spores when surroundings are inhospitable. Plant-like protists include the multi-celled kelp and single-celled organisms like Euglena, diatoms, and the algaes. Like plants, they make their food through photosynthesis. Animal-like protists are referred to as protozoa (meaning first animals) and are single-celled heterotrophs who obtain their food from other organisms. Many, like paramecium, are tiny predators that hunt and consume other single-celled organisms. Thousands of species live nearly everywhere—fresh and salt water, dry sand, moist soil, inside the bodies of living things, and even as parasites.

fUngi

There are more than 77,000 different kinds of fungi, including smuts, rusts, molds, and mildews. This kingdom contains both single-celled (yeasts) and multi-celled organisms (mushrooms). Once classified as non-green plants, we now know that they do not contain chlorophyll and cannot photosynthesize which, clearly distinguishes them from plants. Instead, they obtain food by secreting enzymes that break down organic material into a liquid soup which is then absorbed by root-like structures called hyphae. For this reason they can be referred to as soup eaters. Their nutrition may be received from a living organism (as in the case of athlete’s foot fungus), from dead material (as in bread mold on a hamburger bun), or through a mutualistic relationship (bacteria on the roots of trees, shrubs, or other plants that provide nitrogen to the plant in exchange for the sugars the plant produces through photosynthesis). Plant Kingdom Bryophytes

Tracheophytes

Pterophyta (ferns)

Gymnosperms (cones)

Angiosperms (flowers)

Figure 18.1 Hierarchy within the Plant Kingdom (from simple to most complex) (Drawing by Cindi Smith-Walters)

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Diversity of Life

Plants

Plants are multicellular organisms whose cells contain chlorophyll. This pigment allows them to carry out the process of photosynthesis, which turns carbon dioxide and water into sugars for food and oxygen gas. Plants are found in nearly every place on Earth and are limited in where they grow by the availability of light. Figure 18.1 displays a schematic showing how we split the plant kingdom into two large groups: bryophytes, plants that have no vascular tissue or vessels for transporting plant fluids, and tracheophytes, plants that do have vascular tissues. Bryophytes do not have structures to transport water and nutrients throughout their bodies. They must rely instead on the slow inefficient process of diffusion. Bryophytes include the mosses and are inconspicuous in size and lack true roots, stems, and leaves, but have small root-like hairs called rhizoids to absorb water and nutrients. Trachea means tube, and Tracheophytes have tubes that provide support and a means of transporting water and nutrients. This group is divided into two types—the seedless/spore-bearing vascular plants and the seed-producing vascular plants. Seedless/spore-bearing vascular plants include clubs, horsetails, and ferns. Seed-producing vascular plants include Gymnosperms such as cedars, pines, firs, spruces, and redwoods and Angiosperms such as elms and maples, food-producing plants such as tomatoes and potatoes, and ornamental plants such as roses and tulips.

aniMals

The animal kingdom is the largest kingdom with over 1 million known species. All animals are multicellular and are usually highly mobile and most possess nervous systems, while members of other kingdoms do not. There are 32 phyla of animals and Table 18.4 highlights only a few of the more recognized, starting with the simplest Porifera (sponges) and moving to the most complex, Chordata. Characteristics of importance include body symmetry, number of cell layers, the absence or presence of body systems and overall complexity. We tend to divide animals into the invertebrates (the many phyla without backbones) and vertebrates (the one phylum with). Invertebrates far outnumber vertebrates, even though the latter may be more obvious and familiar.

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Table 18.4 The Most Familiar Animal Phyla*

Phyla Porifera ‘full of holes’

Example/s Sponges

Characteristics Asymmetrical collection of individual cells, with no tissues/organs/organ systems, no nervous system but does have a nerve ‘net’, no skeleton, all water dwelling and are filter feeders, many can filter their entire body volume in less than 1 minute Jellyfish, Radially symmetrical with bodies 2 cell Cnideria layers thick and a hollow body cavity, ‘stinging cells’ Coral, Sea Anemone, no skeleton, stinging cells for capturing Hydra prey, single opening is both mouth and anus, first with muscles and nerves but no organs or organ systems Bilateral (right & left) symmetry, defined Platyhelminthese Flatworms, head and tail, 3 tissue layers but no body ‘no cavity inside’ Tapeworms, Planaria cavity, rudimentary nervous system, many are parasitic, most aquatic but not all Leech, Earth- Bilateral, complete ‘tube within a tube’ Annelida worm gut/digestive system with mouth and ‘segmented anus, complete circulatory system, worms’ simple brain Crustaceans, Bilateral with segments, hard exoskeleton Arthropoda Spiders, Mil- which they must shed to grow, numer‘champions of variation in ap- lipedes, Ticks, ous jointed appendages with specialized Insects wings, legs, antennae, pinchers, etc., first pendages’ phyla to fly, complete digestive system, more species than any other phyla Clams, Slugs, Bilateral, with soft bodies and well deMolluska Snails, Squid, veloped circulatory, nervous, and diges‘prisoner of Oysters, Octives systems. A sheath of tissue (mantle) the shell’ topus covers the body and can secrete a shell if there is one, the mantle cavity houses lungs or gills; a calcium shell is present in most

200

Phyla Enchinodermata ‘spiny skins’

Chordata ‘vertebrates’

Diversity of Life

Example/s Starfish, Sand Dollars, Sea Urchins, Sea Cucumbers

Characteristics Five part radial symmetry, hard but flexible bodies with interlocking plates under a thin skin that is often spiny, they move (slowly), feed, and breathe using a unique water-vascular system ending in tube feet for locomotion, all members live in the ocean, complete digestive system Fish, Amphib- Bilateral with bony skeletons inside, ians, Reptiles, all have a notochord/spinal cord; most Birds, Mamhave a backbone. Increased complexity mals made possible by much more DNA. Jaws (ex: humans) and skills important in their evolution. We tend to think of these as ‘cold’ and ‘warm’ blooded animals with each Class having unique characteristics

* Generally from least complex to most complex

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review QUestions—cHaPter 18 1. A rock is not considered to be alive because a. it does not move. b. it does not reproduce. c. it is simpler in structure than a living thing. d. it does not meet all characteristics of living things. 2. All the following are made of cells except a. animals. b. bacteria. c. plants. d. viruses. 3. According to binomial nomenclature, which two levels of classification are used to scientifically name/represent an organism? a. domain & kingdom. b. class & order. c. genus & species. d. kingdom & phylum. 4. What is the correct order for the levels of classification from most general to most specific? a. domain, kingdom, phyla, class, order, family, genus, species. b. kingdom, domain, phyla, class, family, order, species, genus. c. species, genus, family, order, class, phylum, kingdom, domain. d. class, phylum, order, kingdom, family, genus, species, domain. 5. Members of the fungi kingdom a. are autotrophic. b. are heterotrophic. c. have structures composed of prokaryotic cells. d. contain chlorophyll. 6. A new organism is discovered which is composed of a single microscopic cell that contains a nucleus and chlorophyll. Predict in which kingdom it would be classified. a. Animal. b. Fungi. c. Plant. d. Protist.

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Diversity of Life

7. Fungi consume organic matter and thus play an important role in an ecosystem by a. making nutrients available for recycling back into the soil. b. producing oxygen through photosynthesis. c. producing oxygen through respiration. d. living in mostly aquatic environments. 8. Which statement below is not true about the plant kingdom? a. All members of this kingdom are autotrophic. b. All members of this kingdom are multicellular. c. All members of this kingdom contain reproductive structures called flowers. d. All members of this kingdom photosynthesize. 9. There are many different species of plants in the plant kingdom and not all reproduce in the same fashion. Which method of reproduction is the most common in plants? a. Binary fission. b. Cones. c. Flowers. d. Spores. 10. Into which phylum of the animal kingdom are dogs classified? a. Annelida. b. Chordata. c. Echinodermata. d. Mollusca. (Answer Key: 1.d, 2.d, 3.c, 4.a, 5.b, 6.c, 7.a, 8.c, 9.c, 10.b)

Chapter 19

PLANTS

Patricia Patterson nonvascUlar and vascUlar Plants Plants can be divided into two major categories—non-vascular and vascular (as shown in Figure 19.1). Non-vascular plants do not possess specialized cells organized into tissue systems. All non-vascular plant cells perform the same function for the organism. Seaweeds, moss, hornworts and liverworts are the commonly recognized examples of non-vascular plants. Non-vascular plants are found in aquatic environments and in moist land environments. Some non-vascular plants have different looking “anatomical” features, such as the holdfast of seaweeds, but all cells of non-vascular plants are identical. Vascular plants have four types of specialized tissue that function to support the plant, or produce and transport substances from one part of the plant to another. They are as follows: (a) dermal tissue, the outermost protective layer, (b) vascular (conducting) tissues—xylem and phloem, (c) ground tissue for structural support, and (d) meristem tissue for plant growth. The major categories of vascular plants are based on differences between reproductive structures (spore or seed producers). Seed-producing plants are categorized as cone bearing or flowering, and flowering plants are categorized based on production of a whole or split cotyledon (the fruit that protects the plant embryo).

204

Plants

Figure 19.1 Plant Classification (Drawing by Patricia Patterson)

strUctUre and fUnction of leaves, steMs, and roots Vascular plants have three distinct anatomical parts which are leaves, stems, and roots. They are made of specialized cells and tissues that perform different functions for the plant. Leaves of vascular plants contain cells with chloroplasts that produce chlorophyll needed for photosynthesis (as shown in Figure 19.2). Carbohydrate molecules produced during photosynthesis are transported from the veins of leaves to other parts of the plant. Dermal cells of leaves contain stomata, which open and close to allow the plant to take in or give off air and water.

Plants

205

Figure 19.2 Leaf Structure (Drawing by Patricia Patterson)

Stems connect plants’ leaves to their root systems where nutrients and water are gathered from the soil. In stems xylem and phloem, the vascular tissues, are found bundled together and embedded in pith and cortex, the ground tissues (as shown in Figure 19.3).

Figure 19.3 Stem Structure (Drawing by Patricia Patterson)

206

Plants

Root cells are specialized to absorb water and minerals from soil and make them available to other parts of the plant (as shown in Figure 19.4). Roots and stems can store food the plant manufactures since the vascular system in the stem connects the root and leaf.

Figure 19.4 Root Structure (Drawing by Patricia Patterson)

control MecHanisMs All plants grow, but they grow at different rates and according to different cyclical patterns. Genetic factors, period responses, the action of hormones and enzymes, and tropisms influence patterns of plant growth. Genetic factors determine if plants have a determinate or indeterminate growth cycle. Plants with determinate growth cycles such as annuals and biennials develop, grow, and die in a specific genetically regulated cycle. Plants with indeterminate growth cycles, like most trees, have their growth patterns genetically tied to be regulated by environmental conditions, such as seasons. Period responses govern a plant’s cycles of development and growth in response to day length (photoperiod). Photo-periodicity is a function of seasonality in most parts of the earth. Some common responses of plants to photo-periodicity include the following: (a) flowering of plants (critical night length), (b) halt in the production of chlorophyll, (c) leaf abscission, and (d) the formation of storage organs prior to entering dormancy. Hormones and enzymes are molecules that plants produce in their cells. They are chemical messengers that help plants use less energy for life processes or, in the case of hormones, stimulate growth in response to an environmental stimulus, such as photo-periods.

Plants

207

Tropic responses trigger plant growth that aligns with the directionality of an environmental stimulus. Examples of tropisms are positive (toward) and negative (away from) light (phototropism), and positive (down) and negative (up) from gravity (geotropism). Nastic responses are the movement of some parts of a plant in a manner not related to the directionality of the stimulus. Some common nastic movements occur in response to touch (seismonasty), temperature (thermonasty), or daily light/ dark cycles (photonasty). Seismonasty occurs when plant leaves wilt or close in response to touch, thermonasty occurs when spring flowers, such as the crocus open, and photonasty occurs during the opening and closing of flowers and leaves of some plants in response to light intensity between night and day. Examples include the evening primrose which opens its flowers at night and the morning glory, which closes its flowers at mid-day.

PHotosyntHesis and resPiration Plants both produce and need carbon dioxide, oxygen, and water. Photosynthesis requires carbon dioxide and water and produces oxygen and carbohydrates. Alternatively, respiration requires oxygen and breaks down the carbohydrate molecule, producing water and carbon dioxide (as shown in Figure 19.5). Growth, movement, production of hormones and enzymes, reproduction, transport, and regulation of fluid pressure are all respiration processes that require energy supplied from the breakdown of starch molecules.

Figure 19.5 Relationship Between Photosythesis and Respiration (Drawing by Patricia Patterson)

208

Plants

At dawn and dusk of every day plants experience what is known as equal compensation points, when production and consumption of carbon dioxide, water, and oxygen are equal. At all other times the plant experiences unequal compensation points. During daylight hours, carbon dioxide and water are absorbed and oxygen is given off and during the night, oxygen is absorbed and water and carbon dioxide are given off.

water and nUtrient UPtake and transPort systeMs Plants have mechanisms to regulate uptake, use, and discharge of water. Water regulation is controlled by direct exchange of gases and water vapor with the environment in a process known as transpiration, a passive process requiring no energy. During transpiration plants regulate the flow of oxygen, water, and carbon dioxide in and out of the plant at times of unequal compensation or in response to environmental changes in the amount of water in the environment. When vascular plants need to conserve or release water in response to environmental conditions, guard cells on stomata in dermal tissue will close or open to regulate an internal water balance. Plants transport fluids, nutrients and other substances by means of xylem and phloem tissues located in the stem, leaf, and root. Xylem and phloem cells employ mechanisms of active (requiring energy from the plant) and passive (uses capillary action, gravity and diffusion) transport to move fluids and solutes such as nutrients, hormones and enzymes from organ to organ. Xylem cells are dead cells reinforced with lignin, a tough structural molecule. The xylem tissue transports water and minerals from the root to the stem and leaf making a “one-way” transport system, up from the soil toward the stem and leaf. Osmosis is the process plants use to bring water and minerals through xylem tissue from roots to leaves and stems. Osmosis is diffusion across a membrane in response to differences in pressure (from high to low). As water evaporates or is used in photosynthesis, the pressure in the upper parts of plants becomes less, relative to that below where root cells are absorbing water, and water moves upward through the xylem tubes in response to the pressure gradient. Phloem tissue is lined with living cells and is reinforced with cellulose not lignin, making it more flexible. Phloem transports water and sugars from leaves to other parts of the plant. Starches are assembled from the transported sugars “on site” in the part of a plant where food is stored. Figure 19.6 shows the directional flow of nutrients and water as they are transported by the vascular system in stems.

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209

Figure 19.6 Xylem and Phloem (Drawing by Patricia Patterson)

sexUal and asexUal reProdUction Plants can reproduce both sexually and asexually, making them highly adaptable to diverse environmental situations. All plants have a unique sexual reproductive cycle known as “alternation of generations,” which means that the male and female reproductive cells of every plant species are made by two distinctly different plants known as the gametophyte and the sporophyte. The gametophyte plant generation has a single set of chromosomes (1N), and the sporophyte plant generation has a double set of chromosome (2N) just like higher animals have in all of their cells except for their reproductive cells (gametes). In simple (non-vascular) plants such as mosses and ferns, the gametophyte and sporophyte generations live as distinctly separate plants. In vascular plants the gametophyte generation, though a separate plant, is usually found attached to the far larger sporophyte generation. In seed-bearing plants the male gametophyte is known as the stamen. The stamen produces pollen, which is the male gamete. The female gametophyte of seed-bearing plants is known as the pistel. The pistel produces an ovule, or unfertilized “egg.” A sporophyte generation embryo is created from the fusion of a male (pollen) and a female (ovule) gamete. The sporophyte generation in turn, produces male and/or female gametophytes. Asexual reproduction refers to the process by which new individuals of a species are produced solely from the cells of a single parent. Plants produced asexually from a single parent are called clones because they are genetically identical to the parent plant. All parts of a plant can produce new plants.

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Stems produce new plants from rhizomes, bulbs, corms, or tubers. Rhizomes (runners) are stems near the ground that can form roots, and then shoots. Strawberry plants, irises, day lilies, and ferns are examples of plants that propagate asexually using rhizomes. Bulbs, corms and tubers are underground stems where food is stored, and from which new plants can grow. Tulips, potatoes, and onions are examples of plants that grow from bulbs, corms, and tubers. Roots produce new plants by sending up new shoots from their roots. This is common in many shrubs like boxwood, in plants like bamboo, and in some trees. Leaves of some plants produce new plants on their margins. Coleus is an example of a plant whose leaves produce new plants.

Plants

review QUestions—cHaPter 19 1. Members of the plant kingdom do not share this characteristic a. Are multi-cellular. b. Reproduce by alternation of generations. c. Make their own food. d. Have specialized tissue. 2. Pine Trees can be classified as a. cone-bearing non-vascular plants. b. seed-producing vascular plants. c. monocotyledon seed producing plants. d. spore-producing vascular plants. 3. Seaweeds are classified as non-vascular plants because they a. have no specialized tissues. b. are not green. c. do not have roots. d. do not reproduce by alternation of generations. 4. All parts of a vascular plant contain a. conducting tissue. b. meristem tissue. c. ground tissue. d. all of the above. 5. Determinate and indeterminate growth cycles in plants are governed by a. genetic factors. b. hormones and enzymes. c. photo-periodicity. d. temperature changes. 6. The major role of enzymes produced by plants is to a. help the plant use less energy for chemical reactions. b. tell the plant when to die. c. induce tropic responses. d. tell the plant when to flower.

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7. Plants that open or close their leaves or flowers in response to day and night are exhibiting a. phototropism. b. thermonasty. c. photonasty. d. seismonasty. 8. At dawn and dusk plants experience equal compensation points which means that a. rates of oxygen production and consumption are equal. b. plants take in more carbon dioxide than they give off. c. plants need to take in water from the air. d. plants aren’t photosynthesizing sugar molecules. 9. Nutrients that move through the xylem in the stem flow a. from the root to the leaf. b. from the leaf to the root. c. both to and from the root and leaf. d. none of the above. 10. Plants can create clones which arise from a. stems. b. roots and stems. c. roots, stems or leaves. d. leaves. 11. In alternation of generations a. sporophytes produce other sporophytes. b. gametophytes have the same number of chromosomes as sporophytes. c. gametophytes of more complex plants can’t be seen. d. gametes fuse to produce the sporophyte. (Answer Key: 1. d, 2. b, 3. a, 4. d, 5. a, 6. a, 7.c, 8. a, 9. a, 10. c, 11. d) Works Cited Educational Testing Service (2011). Topics Covered. Middle School Science (0439). http://www.wts.org/Media/Tests/PRAXIS/taag/o439/topics_4.htm, retrieved April 18, 2011. Hamilton, J and C. Robinson., eds. (2005). DK Visual Encyclopedia of Science. New York: Dorling Kindersley Publishing Ltd. Homeostasis: Plants (online reference). University of Hamburg, http:// www.biologie. uni-hamburg.de/b-online/library/at-removed/u3aos23.html. Retrieved April 18, 2011.

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Patterson, B. Patricia (2005 – 2011). Lecture notes for botany unit. Department of Education, Wesley College, Dover, DE, US. Rogers, Kirsteen, L. Howell, A. Smith, P. Clarke, and C. Henderson, eds. (2003). The Usborne Internet-linked Science Encyclopedia. London: Usborne Publishing. Whittles, K. and A. Goldie (1993). Concise Dictionary of Biology. London: Tiger Books International.

Chapter 20

ANIMALS—PART I Kim Cleary Sadler

digestion Digestion involves the breakdown of food into smaller chemical units that can then be used for a multitude of functions by the body. Although no system in the animal body is more important than the other, the only way that animals are able to obtain energy to fuel cellular work and provide raw materials for cells is through food. Intestinal parasites simply absorb nutrients through their body covering, in comparison to animals like earthworms and humans that have a tubein-a-tube body design that permits an ingestive pathway. The process of digestion breaks food down into small molecular units that are the building blocks for life. These building blocks are often listed on a food label and they include carbohydrates (break down into simple sugar or glucose, used for energy), proteins (break down into amino acids, used for body structure and enzymes), fats or lipids (break down into fatty acids, used for energy and protection like oils and waxes), and nucleic acids (break down into nucleotides, used for energy and DNA structure). Mechanical and chemical processes facilitate the breakdown of food through structures in the digestive system. The mouth includes lips, teeth, and a tongue which initiate mechanical breakdown through the process of chewing. The mouth chemically initiates digestion through salivary glands that produce watery saliva with a pH of 7.0 that contains enzymes specific for carbohydrate breakdown. The esophagus is a tube that connects the mouth to the stomach and is composed of smooth muscle which contracts in wavelike motions (peristalsis) to move food toward the stomach. The stomach is a stretchy mucus-protected bag with folds that

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allow expansion to store, mix, and break down proteins. Stomach pH is 2.0–3.0, which is very acidic but protective against pathogens that can cause illness. The digested food moves in a controlled manner through a valve to the small intestine, which is about 30 feet in length. The first several feet of the small intestine continue digestion through enzymes produced by the pancreas which also neutralize acids from stomach. The liver aids in fat breakdown by producing bile which is stored and released from the gall bladder into this part of the small intestine. The remaining portion of small intestine is lined with microscopic finger-like projections called villi that increase surface area for absorption of nutrients into the blood; inside intestinal villi are capillaries and lymph vessels (these structures absorb fatty acids). The small intestine connects to the large intestine which is about 3 feet in length. The large intestine is also known as the colon and the primary function is water absorption. Solid waste produced from food and bacteria is called feces and exits the large intestine through the rectum and anus. Constipation occurs if inadequate water and fiber are included in the diet. The colon also contains diverse populations of bacteria that assist in vitamin K production and immunity.

circUlation The circulatory system in animals can be thought of like a transportation network that brings materials to cells and removes wastes. Animals with simple structural organizations (like a sponge or a flatworm) move substances in and out at the cellular level, whereas complex animals that don’t have most of their cells in contact with the environment have mechanisms for circulating materials to their cells. An open circulatory system, found in insects and some mollusks, pumps blood into an internal cavity that bathes the tissues in an oxygen and nutrient-rich substance. In a closed circulatory system, nutrient and oxygen-rich blood is transported through blood vessels; this system is found in earthworms, squid, and all vertebrates. The structures associated with the closed circulatory system are blood vessels (the transportation pathway), blood (the substance being transported), and the heart (basically a pump that moves the blood within this closed system). Blood vessels that transport blood away from the heart are called arteries; these blood vessels are under tremendous pressure and have thick elastic walls. Arteries connect to arterioles which connect to the smallest blood vessels known as capillaries where nutrient, gas, and waste exchange occurs as blood cells squeeze through in single file. Blood returns to the heart through veins; capillaries connect to microscopic venules which merge to form larger thin-walled veins which contain valves that prevent blood from flowing backwards. The heart has a chamber that receives blood (atrium) and a thick muscularwalled chamber (ventricle) that squeezes the blood through the blood vessel network. Animals that don’t have lungs, like fish, have a 2-chambered heart (1 atrium and 1 ventricle) where blood enters the atrium and exits via the ventricle. Animals

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like frogs and lizards have a 3-chambered heart (2 atria and 1 ventricle) where deoxygenated blood enters the right atria, moves to the ventricle where is it is pumped to the lungs and oxygenated, returning to the left atrium, moving back to the single ventricle, and then pumping blood under pressure, to the body. In the 3-chambered heart there is mixing of oxygenated and deoxygenated blood in the ventricle. Animals with a 4-chambered heart (2 atria and 2 ventricles) have separate circuits that prevent mixing of deoxygenated and oxygenated blood (as shown in Figure 20.1). The pulmonary circuit receives blood on the right side of the heart (right atrium and right ventricle) that moves to the lungs for gas exchange and returns oxygen-rich blood to the left side of the heart. The systemic circuit moves the oxygenated blood from the left side of the heart (left atrium and left ventricle) throughout the entire body. Valves separate the heart chambers and prevent blood from flowing backwards (valves are also found in the large blood vessels connected to the heart). The sound of the heart beating is the opening and closing of the appropriate heart valves. Heart murmurs are caused by heart valves that don’t close correctly and can be detected by listening to the heart with a stethoscope.

Figure 20.1 Diagram of the human heart: trace the pathway with your finger as oxygen-poor blood travels from the body into the vena cava’s to the right atrium, into the right ventricle and to lungs via the pulmonary artery; oxygen-rich blood returns via pulmonary veins to the left atrium, into the left ventricle and pumped to the body through the large aorta. (Drawing by Emily Guitar)

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The rhythmic contractions of the heart are controlled by the autonomic nervous system and specialized patches of heart tissue in the right atrium called the sinoartial node (SA) and atrioventricular node (AV). The SA and AV nodes are the pacemakers of the heart and these patches of tissue first signal simultaneous contraction of the two atria through the SA node, which then signals simultaneous contraction of the two ventricles through the AV node. Heart contraction and rate function is determined clinically through an electrocardiogram (ECG) that detects electrical potential fluctuations. The cardiac cycle has two parts: systole (contraction) and diastole (relaxation). Blood pressure is a function of these two events and arterial pressure is measured with a blood pressure cuff in millimeters of mercury. If your blood pressure is 120/80 your systolic pressure (contraction of the ventricles) is 120 and your diastolic pressure is 80 (relaxation of the ventricles). Cardiovascular disease is a leading cause of death directly related to the accumulation of sticky plaques inside blood vessels that decrease the diameter, thereby increasing blood pressure (think about putting your thumb over a garden hose). When plaques break free and lodge in the blood vessels that nourish the heart, a heart attack occurs. When plaques break free and lodge in the lungs, a pulmonary embolism occurs, and when plaques break free and lodge in the blood vessels supplying the brain, a stroke results. Blood contains essential substances composed of 60% liquid, known as plasma which is primarily water with a pH of 7.4, and 40% cells. The cellular portion is made in the bone marrow and is composed of the following three components: (a) red blood cells (erythrocytes) that transport oxygen gas via hemoglobin, (b) white blood cells (leukocytes) that have nuclei and provide immune function, and (c) platelets which are fragments of cells that enable blood to clot by sticking to breaks in blood vessels and converting a clotting agent into protein fibers that stop blood flow.

resPiration Respiration is the process of breathing or ventilation, where oxygen is inhaled and carbon dioxide is exhaled through various organs associated with the respiratory system. Animals that are very flat and small, like flatworms, are able to obtain oxygen through diffusion because their cells are exposed directly to the environment. More complex animals absorb oxygen through moist surfaces like the skin (earthworms), openings on the body (such as spiracles in insects), gills (fish), or lungs (amphibians, reptiles, birds, mammals). In humans, inhalation moves air in through the contraction of the diaphragm muscle located under the lungs. When the lungs expand or increase in volume, the pressure inside the lungs decreases and air rushes in. During exhalation, the diaphragm muscle relaxes, lung volume decreases, air pressure increases, and air rushes out. Ventilation is a voluntary action and also an involuntary action con-

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trolled by the autonomic nervous system (think about the ability to hold your breath). The carotid arteries, which supply blood to the brain, monitor the pH of the blood through chemoreceptors. Carbon dioxide levels increase when activity levels increase and as carbon dioxide enters the blood plasma, it chemically converts to a bicarbonate ion and a hydrogen ion; this causes the blood to become acidic. In response to the change in pH levels, nerve impulses communicate with the diaphragm muscles and ventilation rate increases. As carbon dioxide is removed from the blood plasma, pH levels return to normal, and ventilation rate slows down. Respiratory system structures associated with gas exchange in humans are located in the head and the chest. Air enters and exists through the nasal cavity (nose, pharynx, larynx) and moves into a passage called the trachea that connects the nasal cavity to the thoracic cavity. The trachea is covered with a movable flap of tissue which prevents food from entering the trachea when swallowing, but opens during inhalation and exhalation. The trachea is lined with cartilage rings that keep the windpipe open—you can feel these rings from the front of your neck. The trachea connects to branching tubes inside the lungs called bronchi and bronchioles that get smaller and smaller in diameter; these transport air in and out of the lungs. Microscopic air sacs called alveoli are located at the end of bronchioles and are covered with capillaries. This is the site of gas exchange in the lungs, where oxygen transported by red blood cells and carbon dioxide from the blood plasma diffuse in opposite directions across the moist alveolar membrane and capillary wall.

excretion Metabolic activity in living things generates by-products that can be toxic to the organism and must be removed efficiently before these products accumulate and cause harm. The primary functions of the excretory system are to regulate the water balance in extra cellular fluid and to remove metabolic wastes, such as ammonia, that cross cell membranes. Animals utilize different ways of regulating excretory processes through structures that collect fluids, selectively filter the fluids, reabsorb what is needed, and excrete what is not needed. For example, marine animals excrete ammonia directly through dilute urine, while birds, reptiles, and insects concentrate ammonia into uric acid (looks like white paste), and amphibians and mammals convert ammonia in the liver to a less toxic form called urea. There are several organs associated with the human excretory system. Humans have a pair of kidneys composed of tissue which contains millions of microscopic filtering units called nephrons. The nephron (shaped like a paperclip with a bulb on one end) is a specialized microscopic structure associated with renal arterioles and capillaries that filter the blood, reabsorb water and other vital substances, and secrete toxic by-products, such as urea. Urine is composed of water, urea, and other unwanted substances filtered from the blood by the nephron and

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is collected in the kidney. Structures called ureters drain urine from the kidney which is stored in the expandable bladder. Nerves and muscles regulate bladder function as urine leaves the bladder through the urethra. This structure is short in length in women but longer in length in men because it runs inside the penis.

iMMUnity The main function of the immune system is to provide protection from foreign invaders (pathogens) that can attack from outside or inside the body. We notice this defense system when we experience inflammation from an injury, feel sick, or suffer from allergies (redness, swelling, runny nose, sore throat, fever). Structures associated with the immune system include lymph nodes, lymph vessels, thymus gland, spleen, and specialized white blood cells made in the bone marrow that circulate between the bloodstream and lymphatic system to coordinate immune system functions. In a healthy person the immune system is always active and like any good defense system, there are multiple levels of security that exist to prevent infections. The first natural or innate level of defense is a nonspecific barrier that is both physical (skin, mucous membranes, and cilia) and chemical (oils, wax, stomach acid, urine, and helpful bacteria). The second level of defense is also nonspecific and becomes available in seconds. When injured, we undergo an inflammatory response. A substance known as histamine causes blood vessels surrounding the injury to leak and permit roaming white blood cells to move freely into the assaulted area. This increase in blood flow to the area causes the inflamed site to exhibit redness, an increase in temperature, swelling, and pain. You experience pain because the swelling puts pressure on nerve endings. Next, proteins in the blood leak into the tissues and assist the white blood cells. Special types of white blood cells can recognize pathogenic molecules and deliver these molecules to specific immune cells called lymphocytes. The third level of immune response is specific to the type of pathogen, infection, or toxin. There are two categories of specific immune responses—antibodymediated and cell-mediated responses. Antibody-mediated and cell-mediated responses are similar to high security identification systems because they can quickly screen pathogenic molecules and remove them. In the antibody-mediated processes, lymphocytes called B cells (which are produced and mature in the bones) secrete antibodies to immobilize pathogens by binding to molecules on the pathogen called antigens. At the same time the antibodies are produced, some B cells are stimulated to become memory B cells that remember this pathogen for future attacks. Vaccinations are effective because when exposed to the same pathogen at a later time, your memory B cells recall those antigens and quickly disable the pathogen.

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In the cell-mediated response, lymphocytes called T cytotoxic cells (killer T cells) recognize foreign antigens and kill the tumor or virus-infected cells. Autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, and acquired immune deficiency (AIDS) are caused by the body’s defense system attacking its own cells or failing to produce the correct type of immune cell. For example, AIDS is caused by the destruction of T cytotoxic cells (killer T cells) by the human immune deficiency virus (HIV).

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review QUestions—cHaPter 20 1. Which of the following is an important feature of the process of digestion? a. The production of white blood cells. b. The provision of nutrients and raw materials for cells. c. The provision of oxygen and removal of carbon dioxide for cells. d. The removal of ammonia-like compounds from the blood. 2. The acidic pH of the stomach provides which of the following? a. Protection from harmful organisms. b. An environment for the growth of harmful organisms. c. Appropriate conditions for the breakdown of fats. d. All of the above. 3. How many chambers are in the human heart? a. 1 atrium and 1 ventricle. b. 2 atria and 1 ventricle. c. 2 atria and 2 ventricles. d. 3 atria and 2 ventricles. 4. Which blood vessel listed is thin-walled and permits exchange of gases and nutrients? a. Arteries. b. Arterioles. c. Capillaries. d. Veins. 5. During inhalation and exhalation, what process describes how oxygen and carbon dioxide move in and out of the alveoli? a. Osmosis. b. Photosynthesis. c. Electrostatic attraction. d. Diffusion. 6. The excretory system a. circulates blood throughout the body. b. maintains the correct water balance in the body and filers the blood. c. produces specialized cells to provide immunity and protection from infectious organisms. d. breaks down food into smaller chemical subunits to nourish the body.

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7. Which of the following relationships is incorrect? a. Kidney...nephron. b. Lung…alveoli. c. Bone marrow…blood cells. d. Large intestine…intestinal villi. 8. During an inflammatory response, which chemical substance causes blood vessels at the injury to leak and bring fluids and white blood cells to the site? a. Histamine. b. Dramamine. c. Atrazine. d. Colchicine. (Answer Key: 1.b, 2.a, 3.c, 4.c, 5.c, 6.b, 7.d, 8.a)

Chapter 21

ANIMALS—PART II Vanessa Hunt

resPonse to stiMUli A change in the external environment that causes an organism to react is called a stimulus. A stimulus often activates one or more of the animal’s senses. Visual stimuli could be as complex as the appearance of a potential mate, or as simple as the appearance of food or a predator. Other stimuli could be tactile (pain or vibrations in the environment), auditory (a mouse hearing an owl hoot, or a bird hearing the song of its own species), or olfactory (smelling food or a predator). Stimuli may also be provided or modified by physical changes in the environment, such as changes in salinity, pH, light, temperature, and oxygen concentration. For example, a male lizard will respond with courtship gestures to the visual stimulus of a female lizard swollen with eggs if and only if he is ready to breed. The male lizard’s breeding readiness is in turn a function of the environmental condition of day length (photoperiod), which attains the correct duration for lizard breeding in the spring months only. A reaction to a stimulus is called a response. The ability to respond to an environmental stimulus is a key characteristic of living organisms. Responses vary with the stimulus and also with the complexity of responses available to the organism. For example, a unicellular organism may contract when touched, where a more complex organism may run, swim, or fly away in response to a tactile stimulus. A moth may respond to the stimulus of a light being switched on by flying toward it, whereas a cockroach is likely to run away from it. Most animal behavior is built on a complex set of responses that also incorporate some physiological reactions to stimuli. A familiar example of a complex

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response to a simple sensory stimulus is the ‘fight or flight’ response. If an animal hears or sees evidence of a predator, it will usually show one or two complex behaviors—fighting or fleeing. Each behavior involves a complex set of physiological responses to the original stimulus or stimuli. Cardiac and respiratory activity may increase, glucose will be released to the bloodstream to fuel muscular activity, digestive activity will slow, blood pressure will change, pupils will dilate, and senses such as hearing and peripheral vision may become temporarily less acute as the organism focuses on the stimulus before it.

HoMeostasis However complex a response to a stimulus becomes, the animal still needs to maintain a stable environment to function properly. This stable internal environment is called homeostasis. Temperature, pH, and ion concentration (including salinity) must be maintained within a narrow range for the cell to function correctly. Such limits are particularly important for the progress of cellular reactions that are catalyzed by enzymes, such as the breakdown of toxic H2O2 in the body to harmless H2O and O2 molecules (catalyzed by the enzyme catalase), and the digestion of proteins in the stomach (catalyzed by the enzyme pepsin). Enzymes such as catalase and pepsin typically only work correctly within certain ranges of temperatures, pH levels, and salinities. Outside of these ranges, the enzyme will become inactivated or break down. Thus it is of critical importance that a stable internal environment is maintained within cells, regardless of changes in the external environment of the animal. In multicellular animals, the different organ systems work together to control the internal environment of the animal, often by negative feedback loops and sometimes by positive feedback loops. A negative feedback loop corrects the stimulus or condition that caused it, whereas a positive feedback loop amplifies or increases the stimulus or condition that caused it. An example of negative feedback is temperature regulation. If the internal environment of an animal is becoming too hot for maximum efficiency (the stimulus), the feedback will be in the form of cooling mechanisms (such as sweating or flushing of the skin as blood vessels dilate) that serve to reduce the stimulus. Conversely, if the internal environment of an animal becomes too cold, feedback will be in the form of production of extra metabolic heat (requiring calories to be burned) that reduce the stimulus. Positive feedback loops that function in homeostasis occur less frequently than negative feedback loops. One example occurs in the process of blood clotting, The positive feedback loop is initiated when injured tissue releases signal chemicals that activate platelets in the blood. An activated platelet releases chemicals to activate more platelets, causing the rapid formation of a blood clot. Another example is in mammalian lactation, or nursing: the more the baby suckles, the more milk is produced, via a surge in prolactin secretion.

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The endocrine and the nervous systems are the major homeostatic control systems in higher animals, although most systems have some homeostatic components. The endocrine system works to bring about homeostasis more slowly, and with more persistent effect than the nervous system. The nervous system is involved in more rapid responses to deviations from normal conditions, such as the temperature regulation described above.

endocrine systeM The endocrine system consists of eight major glands (as shown in Figure 21.1) that produce hormones, chemical messengers that act upon and regulate the activities of cells and organs that have specific receptor sites for these hormones (a stimulus-response mechanism in each case). Hormones are secreted into the bloodstream by the manufacturing gland and delivered to the target organ by the circulatory system. The major endocrinal glands and the hormones they produce are described below.

Figure 21.1 Endocrine System (Drawing by Megan Ritchie)

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The Hypothalamus is located in the middle of the base of the brain and is approximately the size of a pea. It produces hypothalmic-releasing and release inhibiting hormones that stimulate or suppress the release of hormones in the anterior pituitary gland. Thus the hypothalamus serves to regulate the hormones of the anterior pituitary. The anterior pituitary is located below the hypothalamus and is the size of a small bean. Specific hypothalmic hormones bind to receptors on specific cells of the anterior pituitary, and stimulate or inhibit release of the hormones produced here. Four of the hormones produced by the anterior pituitary gland are described below. Growth hormone works to stimulate protein, fat, and carbohydrate metabolism, bone growth, and muscle growth. Thyroid stimulating hormone or TSH stimulates the thyroid gland to release thyroid hormones. Thyroid hormones target more cells in the body than any other hormone, affecting cellular differentiation, growth, and metabolism, and have important effects on normal development and growth. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) target the ovaries and testes, and are important regulators of reproductive functions. The posterior pituitary gland is an extension of nerve tissue from the hypothalamus that sits behind the anterior pituitary. This tissue is a storage site for two hormones, antidiuretic hormone (ADH) and oxytocin (OT). Antidiuretic hormone increases the reabsorption of water by kidney tubules, thus decreasing the amount of urine produced. Oxytocin stimulates uterine contractions during childbirth, and release of milk from the mammary glands when nursing The thyroid gland is one of the largest endocrine glands and is located in the neck. It produces two thyroid hormones, tri-iodothyronine (T3) and Thyroxine (T4), that travel though the blood to all tissues of the body. These two hormones increase metabolism of food, thereby increasing energy and heat production, and they also increase the rate of protein synthesis The parathyroid gland consists of four small parathyroid glands, approximately the size of a large rice grain, located on the back of the thyroid gland. They secrete parathyroid hormone (PTH) which is used to maintain proper blood calcium levels The adrenal cortex secretes three types of steroid hormones. These hormones promote growth during puberty, supplying estrogen to males throughout life and to women after menopause. They are also responsible for maintaining normal blood pressure and volume. The adrenal medulla secretes epinephrine (adrenalin) and norepinephrine (noradrenaline) in response to stress. Epinephrine and norepinephrine released from the adrenal medulla have the same effects on target organs as direct stimulation by sympathetic nerves, although their effect is longer lasting. The pancreas is located in the upper left portion of the abdomen and functions in digestion in addition to being part of the endocrine system. Certain cells in the pancreas called islets of Langerhans produce the hormones glucagon and insulin. Glucagon stimulates the liver to break down glycogen into glucose and to convert

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fats and amino acids into energy for metabolic use. Insulin is an essential hormone because it allows glucose to enter cells from the bloodstream by increasing the permeability of cell membranes to glucose. The ovaries are located in the pelvic cavity of females on either side of the uterus and produce the hormones estrogen and progesterone. Estrogen has several functions, including promoting the maturation of the egg and stimulating the growth of the lining of the uterus for implantation of a fertilized egg. Progesterone also prepares the endometrium to become a potential placenta by promoting the storage of glycogen and the growth of blood vessels. The testes secrete androgens such as testosterone that orchestrate the growth and development of the male reproductive system and trigger male puberty later in life. Bird songs, amphibian calls, the deeper voice of adult male humans, facial hair, colors in the feathers of male birds, the skin of male fishes, muscle mass, and behaviors such as sex drive and aggressiveness are mediated by androgens.

nervoUs control Responding to stimuli in the external and internal environment is critical to animal survival, and it is the nervous system that mediates this stimulus-response process. The nervous systems of most invertebrate animals are relatively simple, consisting of fewer neurons (nerve cells) arranged in less complex networks than in vertebrate animals. More elaborate nervous systems provide for more nuanced and complex responses to stimuli. As the complexity of nervous control increases in animal groups, it is accompanied by increased cephalization (the increasing concentration of nervous tissue toward the anterior or ‘head end’ of an organism) and the appearance of a brain to process and coordinate responses to information. The basic unit of communication in the nervous system is the neuron—a cell specialized for communicating electrochemical information. Although a neuron is sometimes called a nerve cell, a nerve is a name for a bundle of axons enclosed in a sheath that provides a common pathway for the transmission of impulses. A cluster of interconnected nerves is called a ganglion (plural: ganglia). Neurons have a fundamental three-part structure consisting of dendrites for input, an axon for conduction of the signal, and axon endings for output or response (as shown in Figure 21.2). Individual neurons connect with one another at junctions, called synapses. When an electrochemical nerve impulse reaches the synapse, it releases a neurotransmitter (a chemical messenger that conveys information in the nervous system) that diffuses across the synapse and triggers a new impulse in the dendrites of adjacent neurons.

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Figure 21.2 Neuron (Drawing by Megan Ritchie)

inverteBrate aniMals Simple invertebrates such as Cnidarians (a group of aquatic animals that includes jellyfish, corals, sea anemones, and hydras) have a rudimentary network of neurons called a nerve net (as shown in Figure 21.3). In such nerve nets, a neuron typically extends into each region of the body, such as the anemone tentacles or the sea star “arms.” Each neuron is connected to others by a network, but there is no brain to coordinate impulses when a neuron is stimulated. The nerve impulses are conducted in all directions from the point of stimulation, throughout the entire “nerve net.” There is no means of processing the information to make a specific response; thus, the nerve net provides only very general responses to the environment.

Figure 21.3 Cnidarian Nervous System (Drawing by Megan Ritchie)

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In Echinoderms (the sea stars, sea urchins, and sea cucumbers), the nervous system is a little more complex. A nerve ring surrounds the mouth of the sea star in the central disc, and this ring connects the radial nerves that branch through each arm. This centrally located nerve ring enables coordinated movement of the animal’s five arms (as shown in Figure 21.4)

Nerve Ring

Radial Nerve Cord

Figure 21.4 Echinoderm Nervous System (Drawing by Megan Ritchie)

Other invertebrate groups, such as arthropods and mollusks, show a trend toward greater cephalization. In Arthropods (the largest animal phylum that includes insects, spiders, and crustaceans), the head region contains a brain (two pairs of ganglia) which receives nerve impulses from highly developed sensory structures such as antennae and compound eyes. The information received is then sent to other parts of the body through a ventral (lower surface of the animal) nerve cord that in turn differentiates into a pair of ganglia in each body segment. This arrangement of sophisticated sensory structures connected to a brain that can relay responses to other areas of the body is very effective, as evidenced by the difficulty of swatting a fly, as it detects movement and responds with reflexive escape behaviors. The phylum Platyhelminthes (bilaterally symmetrically flatworms, such as planaria), have a somewhat more specialized, although still simple, nervous system. This phylum is where neurons are first observed organized into bundles surrounded by connective tissue (ganglia). There is also a rudimentary brain consisting of a pair of ganglia at the anterior end of the animal, which is connected by two longitudinal nerve cords (bundles of nerves) to the nerve nets throughout the rest of the planarian body (as shown in Figure 21.5). The ganglia receive stimuli from the sensory structures (including a pair of eyespots that respond to light) and transmit them up longitudinal nerve cords to the brain, which then directs specific responses from the muscle cells. Thus flatworms have sufficient nervous system apparatus to make specific responses to stimuli such as retreating when touched or moving away from light. The brain and two longitudinal nerve chords of the flatworm constitute the simplest central

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nervous system (CNS) known among the animals. The remainder of the nerves are collectively known as the peripheral nervous systems (PNS).

Figure 21.5 Phylum Platyhelminthes Nervous System (Drawing by Megan Ritchie)

Mollusks (including snails, mussels, clams, octopuses, and squid) vary in the degree of cephalization. However, molluscan nervous systems do have a basic common plan, based upon a pair of longitudinal nerve cords, one dorsal (running the length of the back of the animal) and one ventral (running up the lower surface of the animal). There are paired nerve connections to major sensory sites and sensory organs.

verteBrate aniMals Vertebrate animals (fishes, reptiles, amphibians, birds, and mammals) have the most specialized nervous systems, with a central nervous system (CNS) consisting of a brain and spinal cord, and a peripheral nervous system (PNS) consisting of ganglia and nerves that enable the central nervous system to communicate with the remainder of the organism’s body (as shown in Figure 21.6). The vertebrate nervous system is highly cephalized, with the majority of neurons concentrated in a brain located in the head of the animal. Every chordate embryo has a hollow nerve cord that becomes the brain and spinal cord, and together these comprise the central nervous system. The original nerve cord, or neural tube, is subdivided into forebrain, midbrain, and hind brain subdivisions, with the hindbrain contiguous with the anterior end of the spinal cord. Both the spinal cord and the brain consist of “white matter” and “gray matter.” White matter refers to bundles of axons coated with a sheath of myelin, an insulating substance composed of protein and lipids that also serves to propagate nerve impulses. Gray matter is composed of the nerve cell bodies and dendrites. In the spinal cord, the white matter is at the surface, and the gray matter inside. This pattern is reversed in the brain, where the gray matter is on the outside (the cerebral cortex) and the white matter inside.

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Figure 21.6 Human Nervous System (Drawing by Megan Ritchie)

The peripheral nervous system is divided into the afferent system, which delivers stimuli to the brain, and the efferent system, which delivers responses from the brain to the skeletal muscles, smooth muscles, and glands (known collectively as the effectors). The efferent part of the PNS is further divided into the somatic system (signaling the skeletal muscles) and the autonomic system (signaling the smooth muscles and glands). The somatic system controls the contraction of skeletal muscles, producing body movements. Although the somatic system is primarily under conscious and voluntary control, some contractions of skeletal muscles are unconscious and involuntary. These include the reflexes, shivering, and constant muscle contractions that maintain body posture and balance. The processes controlled by the autonomic nervous system are mostly involuntary, and include digestion, sweating, blood circulation, various functions of the reproductive and excretory systems, and contraction of smooth muscles throughout the body. The autonomic nervous system contains two subdivisions— the sympathetic and parasympathetic nervous systems, which are always active, and have opposing effects on the organs they affect, enabling precise control. For example, in the circulatory system, sympathetic neurons stimulate the force and rate of the heartbeat, and parasympathetic neurons inhibit these activities. In the digestive system, sympathetic neurons stimulate the movement of materials through the small intestine, and parasympathetic neurons inhibit these activities. These opposing functions of stimulation and inhibition enable precise regulation of involuntary body functions.

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The sympathetic division of the autonomic nervous system is most influential in situations involving psychological or physical stress. Under such conditions, signals from the sympathetic division increase the heart rate, constrict blood vessels and raise blood pressure as a result, dilate the bronchioles of the lungs to aid breathing, induce sweating, and dilate the pupils to enhance vision. Activities that are less important in an emergency, such as digestion, are suppressed by the sympathetic system. In contrast, the parasympathetic division is most influential in lower stress situations and physiological maintenance activities such as digestion, insulin secretion, and immune system activity.

tHe MUscUloskeletal systeM The skeleton is an interconnected system of bones that has four major functions. First, bones serve to support the body, and to protect certain internal organs from injury. For example, the skull protects the brain, and the rib cage protects the heart and lungs. Second, bones provide locomotion as they are moved at the joints by the contraction of attached muscles. A joint is where two adjacent bones or combination of bones and cartilage meet. Third, bones are responsible for blood cell production. The active bone marrow found in certain bones is the primary tissue responsible for the formation of blood. Fourth, bones regulate blood calcium levels. Excess calcium is stored in bone tissue, and can be removed to maintain an appropriate level of calcium in the blood. Blood calcium is critical to functioning of muscles and nerves, and is necessary for blood clotting.

divisions and coMPonents of tHe HUMan skeleton

The human skeleton contains 206 bones, (as shown in Figure 21.7), connected by ligaments. It is divided into the axial skeleton and appendicular skeleton. The axial skeleton includes the bones of the skull, the hyoid bone, the middle ear bones, the vertebral column, and the bony thorax. The appendicular skeleton includes the bones of the limbs and the bones of the pelvic (hip) and shoulder girdles. Descriptions of the components of the axial skeleton are given by Table 20.1 and descriptions of the components of the appendicular skeleton are given by Table 20.2.

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Figure 21.7 Human Skeleton (Drawing by Megan Ritchie) Table 21.1 Bones of the Axial Skeleton

Skull

Braincase consists of eight cranial bones. Face consists of 14 facial bones. Immovable joints between bones are called sutures. Paranasal sinuses are air cavities that lighten the skull and provide resonance for the voice. Vertebral Supports trunk and head and protects spinal cord. Individual bones Column or vertebrae as follows: seven cervical, 12 thoracic, 5 lumbar, 5 sacral, 4-5 coccygeal (fused into coccyx). Cartilaginous discs act as shock absorbers between adjacent vertebrae. Rib cage Sternum and 12 pairs of ribs. All ribs articulate with thoracic vertebrae. True ribs (first seven pairs) also articulate directly with sternum via costal cartilages; false ribs (pairs eight, nine, and ten) articulate with costal cartilage; floating ribs (pairs eleven and twelve) do not articulate ventrally.

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Table 21.2 Bones of the Appendicular Skeleton

Shoulder

Scapula with shoulder muscles. Articulates with humerus of upper arm. Clavicle (collarbone). Braces the scapular Arm Humerus (upper arm). Articulates with scapula and ulna (elbow). Radius and Ulna (forearm). Aarticulate with each other and the carpals (wrist) Wrist and Eight Carpals (wristbones), five metacarpals (hand bones), five Hand phalanges (fingers). P e l v i c Two hip bones, each composed of three fused bones: ilium, ischium, Girdle and pubis. Articulate with femur (thigh bone) at the acetabulum. A n k l e Seven tarsals or ankle bones. Calcaneus or heel bone. Five metatarand Foot sals or foot bones. Fourteen phalanges toes. Two phalanges make up each big toe, and three phalanges are in each of the other toes

Bone tissUe

Bones are organs made up of bone tissue, bone marrow, blood vessels, epithelium, and nerves. Bone tissue is composed of a bone matrix and bone cells. The matrix is composed of calcium salts and collagen. The calcium level in this matrix changes constantly as calcium is removed from bone and taken into the blood, and is restored to the matrix by dietary calcium. The function of the bone cells is to regulate the calcium level in the bone matrix. Bone tissue is divided into compact bone and spongy tissues. Compact bone forms the hard exterior of the bones and spongy tissue fills the interior. The tissues are identical in their components, but differ structurally. Ossification is the process of forming new bone tissue, and occurs when bones form in fetal development, and when they grow or heal.

forM and fUnction in Bones

Bones are extremely varied in size and shape, from the pea sized wrist bones to the long bones of the thigh. The form of the bone reflects its function in the skeletal system. Bones are generally classified into the following groups: 1. Long bones: bones where length exceeds width, such as the arm and leg bones. 2. Short bones: tiny cube-shaped bones, such as those found in the wrist and ankles, predominantly composed of spongy bone. 3. Flat bones: thin, flat, and curved bones, such as those that form the ribs, breastbone, and skull. 4. Irregular bones: bones that cannot be classified as long, short, or flat. They include the hip bones, vertebrae, and various bones in the skull. 5. Sesamoid bones: small round bony masses embedded in certain tendons that may be subjected to compression and tension. The largest sesamoid bone is the patella, which is embedded in the tendon of the quadriceps femoris at the knee.

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tHe MUscUlar systeM tHe Major MUscles of tHe Body

The human body contains more than 600 muscles which are divided into four groups, including muscles of the head and neck, muscles of the trunk, muscles of the arm and shoulder, and muscles of the hip and leg (as shown in Figures 21.8 and 21.9). The majority of the muscles are attached to the bones by tendons and the primary function of this system is to move the skeleton. A secondary function is the production of heat, contributing to the maintenance of a stable body temperature (homeostasis).

Figure 21.8 Anterior Muscles (Drawing by Megan Ritchie)

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Figure 21.9 Posterior Muscles (Drawing by Megan Ritchie)

The electrochemical impulses that cause muscles to contract are transmitted by the nervous system. Contraction of muscles for even the smallest movement is ultimately dependent on the brain. The motor areas of the frontal lobes of the cerebrum generate electrical impulses that travel along the motor nerves to the muscle fibers. The brain also regulates changes in heart rate, respiratory rate, and the diameter of blood vessels. Coordination of movements that require alternate contraction and relaxation of muscles, such as walking, is also regulated by the brain. The circulatory system becomes involved as heart rate increases during muscular contractions that produce movement. This system is also responsible for delivery of oxygen to the muscles via the bloodstream, and in removal of waste products such as carbon dioxide and lactic acid.

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MUscle strUctUre and arrangeMent

Skeletal muscles are composed of thousands of individual muscle cells, also known as muscle fibers or myocytes. Muscle cells work by contraction, in which they shorten and pull upon an attached bone to produce a movement. The number of fibers in a muscle that actually contract during a specific task is dependent upon the amount of work to be done. Opening a curtain will involve contraction of fewer muscle fibers than opening a heavy door. Muscles are generally arranged around the bones of the skeleton as antagonists or synergists. Antagonistic muscles have opposing functions. For example, the biceps muscle on the front of the upper arm, and the triceps muscle at the back of the arm are antagonists. The biceps contracts, shortens, and flexes the forearm, bending the elbow. The triceps contracts, shortens, and extends the forearm, straightening the arm. Joints that can move in a variety of directions require several sets of antagonists. Synergistic muscles work together to perform the same function. When the biceps muscle flexes the forearm and bends the elbow, as described previously, two additional muscles work in synergy to accomplish this. The particular contribution of each muscle depends on the position of the hand. Different muscles are called into play, depending on the rotation of the palm. Note that the difficulty of some movements depends on the position of the hand. Chin-up exercises are easier with the palms toward the face, as this position allows stronger muscles in the synergistic group to be the prime movers. Stabilizing a joint during movement, such as the contribution of the shoulder muscles to the action of the biceps for the fine movement required when raising a glass to the mouth, is also synergistic.

soUrces of energy for MUscle contraction

Contraction of muscles is largely an aerobic activity, thus involving the respiratory system. Adenosine Triphosphate, or ATP, provides the energy needed for muscle fibers to contract. A single muscle fiber may contain several billion filaments, each of which uses 2500 ATP molecules per second when actively contracting. Very little ATP is stored in muscle fibers. A resting fiber contains enough ATP to initiate a contraction, after which ATP must be generated at the same rate it is used. Cellular respiration, which produces ATP from the breakdown of glucose in the presence of oxygen must therefore increase as muscles contract. In turn, this demand for oxygen increases the respiratory rate. Carbon dioxide is a waste product of cellular respiration and must be exhaled, again involving respiratory activity.

anatoMy of skeletal MUscle

Each skeletal muscle is attached at its origin to an area of bone. The other end of the muscle is called the insertion point and is attached to a second bone by a tendon. Each muscle is composed of thousands of cylindrical muscle fibers that

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run from the origin to the insertion, and are bound together by connective tissue. Blood vessels and nerves run through the muscle via this connective tissue. The muscle fiber consists of an array thousands of contractile units called sarcomeres, which are arranged longitudinally to form cylinders called myofibrils (as shown in Figure 21.10). Thick filaments of the protein myosin are at the center of the sarcomere, and thin filaments of the protein actin are at the ends. It is this arrangement of filaments that gives skeletal muscle a striated appearance. The sarcomere is surrounded by the sarcoplasmic reticulum, which is the muscle cell analogy for the endoplasmic reticulum of other cell types. The sarcoplasmic reticulum stores calcium (Ca2+) ions, essential to the contraction process. Muscle Fiber

Myofibril Sarcomere

Figure 21.10 Muscle Fiber (Drawing by Andrew Cross)

tHe contraction Process:

A relaxed muscle cell has a resting potential via an electrically polarized sarcolemma. The outside of the sarcolemma is positively charged relative to the inside. Sodium (Na+) ions are concentrated outside the cell, and potassium (K+) and negative ions are concentrated inside the cell. Contraction begins with the arrival of a nerve impulse at the tip of the motor neuron, which stimulates the release of acetylcholine. Acetylcholine generates electrical changes by opening sodium channels and the movement of sodium (Na+) ions into the muscle cell and a small voltage, called an action potential, is created in the muscle fiber. This action potential stimulates release of Ca2+ ions from the sarcoplasmic reticulum. This initiates events within the muscle fiber that bring about contraction of the actin and myosin proteins, resulting in each sarcomere in the fiber shortening. This shortening or contraction occurs as actin and myosin fibers sliding over each other.

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review QUestions—cHaPter 21 1. Most animal behavior involves which of the following types of reactions? a. Psychological. b. Anatomical. c. Physiological. d. Emotional. 2. Which of the following maintains a state of physiological balance within a living organism? a. Reproductive hormones. b. Fight or flight response. c. Homeostasis. d. Digestion. 3. Which of the following factors are responsible for the proper functioning of enzymes? a. Temperature, pH, and ion concentration must be maintained within a narrow range. b. Oxygen concentration, pH, and light must be maintained within a narrow range. c. Adequate nutrients must be available. d. Genetic factors are entirely responsible for enzyme functioning. 4. In which of the following does a negative feedback loop occur? a. Blood pressure regulation. b. Childbirth. c. Blood clotting. d. Fight or flight response. 5. A hormone affects ____________. a. all tissues b. tissues that have receptors for that hormone c. reproductive tissues d. tissues in need of repair 6. Which of the following glands regulates the body’s metabolism? a. Hypothalamus. b. Thyroid. c. Adrenal Gland. d. Parathyroid.

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7. Which part of the neuron is responsible for receiving electrical responses? a. Synapse. b. Axon. c. Filament. d. Dendrite. 8. The phyla below are characterized by nerve nets and lack of a brain with the exception of the _________. a. Echinoderms b. Cnidaria c. Vertebrates d. Platyhelminthes 9. Which system found in vertebrate animals is most influential during an emergency? a. Central Nervous System. b. Sympathetic Nervous System. c. Parasympathetic Nervous System. d. Peripheral Nervous System. 10. Which of the following is not a primary function of the bones? a. Regulation of calcium levels. b. Production of blood cells. c. Protection of vital organs. d. Control of muscles. 11. Which of the following is a function of the muscular system? a. Production of heat. b. Transmission of nerve impulses. c. Protection against disease. d. Regulation of hormone levels. 12. Muscle fibers are composed of which of the following? a. Sarcomeres. b. Membranes. c. Nerve endings. d. Hormones. (Answer Key: 1.c, 2.c, 3.a, 4.c, 5.b, 6.b, 7.d, 8.c, 9.b, 10.d, 11.a, 12.a)

Chapter 22

ECOLOGY Peter Rillero

PoPUlation dynaMics Perhaps you have observed a deer, coyote, raccoon, oak tree, or cactus in the wild. This organism is part of a population composed of all the other organisms of the same species living in a particular area. The organism interacts with other species in the area. All the species in the area are called a community. Members of the community interact with the nonliving environment, such as parts of the soil, air, light, and water to form an ecosystem. The factors of an ecosystem are biotic (living) and abiotic (not living). This chapter explores the interactions that occur in ecosystems and describes common terrestrial and aquatic ecosystems.

social BeHaviors Whether in real life or nature films, observing social behaviors (interactions between animals of the same species) can be fascinating. Altruism exists when an animal does a good thing for a member of the same species, such as a member of an elephant herd nuzzling a calf in the right direction. Dominance is observed when one or more group members play a controlling role with the members, such as with the alpha pair of wolves. The dominant male and female wolf have the most freedom; they choose the best places to sleep and get access to the food first. Other wolves follow their lead, depending upon their hierarchy in the pack. Wolves, like many other animals, also show territoriality as a social behavior. Territoriality is the pattern of behaviors that are used to defend a geographic area

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against other members of the same species. A male wolf or dog marking his territory with scented urine in strategic areas is an example of a territorial behavior.

intrasPecific coMPetition Intraspecific competition occurs when members of the same species vie for the same resources. As populations increase in size, the competition can intensify. When a small population is introduced into an area where the organisms obtain their needs and can avoid predators, the population is likely to grow exponentially. A graph of population growth (y-axis) versus time (x-axis) for organisms in this situation typically resembles the letter J, as shown in Figure 22.1, and for this reason this is called a J-shaped curve.

Figure 22.1 A J-shaped growth pattern indicates population growing without limiting factors. (Drawing by Peter Rillero)

As the population increases, more organisms live in the same area, increasing the population density, and competition between organisms increases. There will eventually be one or more essential factors that are in short supply, and these become limiting factors for population growth. The growth rate slows and the population may remain at a relatively constant level. A graph of population growth versus time for organisms in this situation resembles the letter S, as shown in Figure 22.2, and for this reason this is called an S-shaped curve. The term carrying capacity refers to the maximum number of organisms of a species (or population size) that a particular area can support. In the graph, the carrying capacity is indicated with the letter K.

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Figure 22.2 A population grows until it reaches the carrying capacity of the area. (Drawing by Peter Rillero)

Species that are physically larger living in stable areas, like antelope in a savannah, tend to exhibit the S-shaped growth patterns. These organisms typically produce relatively few offspring and they care for their offspring well. Organisms with this type of lifestyle are called K-selected. On the other hand, smaller organisms such as mosquitoes that live in areas where environmental conditions frequently and dramatically change, often produce large amounts of offspring with little or no parental care. In favorable conditions, large numbers of offspring will reach adulthood and reproductive age. As adults they again produce large numbers of offspring, which causes a massive peak in the population size. Because environmental conditions change or the population size is unsustainable, the population eventually crashes. Species with this growth pattern are called R-selected.

intersPecific relationsHiPs Interspecific relationships are relationships that occur between two different species. In a community, a herbivore seeks to eat plants, a carnivore seeks to eat animals, and an omnivore seeks to eat either plants or animals. One category of interspecific relationships in a community is called predator-prey relationships, and these occur when animals seek other animals to eat. Speed and heightened senses are necessary for the predator to get its food or for the prey to escape. The interactions of a species and the characteristic of those species that enhance their survival help define the niche of that species. We can begin to describe the niche

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of a southern white rhinoceros as grass-eating, diurnal, taking good care of its offspring, and having the ability to protect itself from predators due to its enormous body size, two horns, and super thick skin. Another category of interactions in a community is called symbiosis, which is a situation that results when two or more species live in proximity to enhance the survival of at least one of the species. There are three types of symbiosis. In mutualism, both species benefit from the close interaction. For example, a lichen, which you might see growing on a rock or tree, is actually two species living together. The fungus provides the container for the algae. The algae conduct photosynthesis and provide nutrients for the fungus and itself. In commensalism one species benefits, while the other has negligible or no impact from the association. An orchid growing on a branch of a tree in a rainforest is an example of commensalism. The orchid benefits from being higher up from the ground to get light but because the orchid doesn’t absorb nutrients from the tree, the tree is not affected. In parasitism the relationship is definitely win–lose because the parasite gains at the expense of a host. A tapeworm living in your intestine would steal nutrients from you as it grew and produced thousands of eggs.

sUccession Imagine a volcanic island emerging from the sea as just a lump of rock. In time, erosion weathers the rock into smaller particles. Wastes from birds mix in with the particles. Some small spores and seeds carried from other landforms settle and grow. First moss and grasses appear, then larger bushes, and after a much longer time trees would appear. The gradual change in life in an area is called succession. Primary succession occurs in a place that has never had life; secondary succession occurs when a natural area is disturbed such as in a forest fire.

staBility of ecosysteMs and tHe effects of distUrBances Ecosystems are composed of living organisms and the non-living environment. To be sure, living things interact, such as when one organism eats another for food. The living and nonliving interactions are also important such as a plant using sunlight, carbon dioxide, and water to produce glucose molecules. Certain types of communities tend to form in certain areas. The most obvious characteristic of a community is the vegetation or type of plants that grow in the area, such as trees, bushes, grasses, or cacti. The vegetation that grows is influenced by the amount of light, water, and the temperatures in the area. The stable community that develops in an area is called the climax community. This could be a beechmaple forest in the northeastern part of the United States, a ponderosa pine forest in northern Arizona, a tropical rainforest in Costa Rica, or a savannah in Kenya. While a climax community is relatively stable, disturbances of the ecosystem can occur on small and large scales. These disturbances can be natural, such as

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a fire or flooding, or the result of human impact such as clear cutting forests or converting natural areas into places for human activities. In 1988, Yellowstone Park had a fire that burned 793,000 acres (36% of the park) of forest dominated by lodgepole pine trees. Little was left on this land except scorched soil. The first plants to return were small, fast growing plants and grasses. Then bushes gradually appeared, and overtime trees returned through the process of succession.

energy flow Light energy from the Sun provides the “fuel” for the ecosystems you have experienced. By combining atoms from carbon dioxide and water, photosynthetic plants and algae convert the light energy into the energy stored in organic molecules, such as sugars and other carbohydrates, fats, and proteins. The photosynthetic organisms use these molecules for growth and repair or break these molecules apart, yielding energy for use. Herbivores eat the photosynthetic organisms and obtain the energy-rich organic molecules, which they can also break to use the energy. Carnivores feed on the herbivores and also obtain the energy-rich molecules. The path of energy through an ecosystem can be depicted as a food chain, such as shown in Figure 22.3. Usable energy is continually lost from the system, as organisms use the energy to supply their energy needs. While materials are used over and over again, it is important to realize that organisms in the ecosystem do not recycle energy. It is used and converted to other energy forms, such as heat energy, that are no longer available to meet the energy needs of living things. Thus, new energy must be constantly supplied, and this is done through the Sun’s energy and photosynthetic organisms.

Figure 22.3 A food chain shows the flow of energy and matter in an ecosystem. (Drawing by Peter Rillero)

BiogeocHeMical cycles While energy makes a one-way journey through living organisms, matter is continually recycled. The molecules in you today were not only in the living things of the food chains you are part of, but your molecules were in millions of other living organisms. There are three important cycles that play a role in this process: (a) the carbon cycle, (b) the nitrogen cycle, and (c) the water cycle.

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carBon cycle

All organic molecules have a carbon framework. Glucose, for example, has a chain of six carbon atoms that make a loop. The carbon atoms connect to other carbon molecules and most also have a hydrogen (H+) and hydroxide ion (OH-) attached. Plants use the energy in sunlight to split hydrogen from oxygen in water molecules and combine hydrogen and carbon dioxide molecules to eventually form glucose. From glucose, other organic molecules are made, including more carbohydrates, fatty acids (for making oils), and amino acids (for making proteins). In photosynthesis, plants and algae pull carbon dioxide out of the atmosphere and release oxygen. The carbon cycle is shown in Figure 22.4. In respiration, plants and animals use oxygen to break these energy-rich molecules to liberate energy in useful forms for the organisms. The two waste products produced as a result of this are carbon dioxide and water. Respiration returns carbon dioxide to the atmosphere.

Figure 22.4 The carbon cycle shows the flow of carbon between living things and the non-living environment. (Drawing by Peter Rillero)

Combustion is similar to respiration, in that oxygen is used to liberate energy from energy-rich molecules, with carbon dioxide given off. So if wood is burning or gasoline is combusted in an automobile engine, carbon dioxide is given off.

nitrogen cycle

Nitrogen is an important element in amino acids, the building blocks of proteins, and in nucleic acids, such as DNA and RNA. The availability of nitrogen in soil can be a limiting factor for plant growth. Although 78% of the atmosphere is ni-

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trogen, this exists as N2, which is a very stable molecule and not usable by most living things. Plants absorb their nitrogen from the soil, and there are several ways for the soil to get this nitrogen. One way is through nitrogen-fixing bacteria in the soil that can use atmospheric nitrogen and convert it to forms that can be absorbed by plant roots. Some nitrogen-fixing bacteria live in root nodules of leguminous plants, such as beans. In this mutualistic relationship, the bacteria provide the usable nitrogen compounds and the plant provides carbohydrates. Lightning can also help convert stable N2 molecules into usable forms. Since nitrogen is a component of living things, the decay of living materials returns nitrogen into the soil. Humans may also add nitrogen fertilizers to areas, which can increase plant growth. Run off of the extra nitrogen, however, may negatively impact other areas, especially aquatic ecosystems.

BioMes Biomes are major regions of the world composed of communities. The most common terrestrial biomes are deciduous forests, tropical rainforests, deserts, grasslands/savannas, taiga, and tundra. To be sure, species that exist in grasslands in Tanzania are different than the species that exist in grasslands in Russia; however, they resemble each other because the similar climates and soil conditions create similar ecosystems. The terrestrial biomes are summarized in Figure 22.5.

Figure 22.5 Biomes are influenced by temperature and precipitation. (Drawing by Peter Rillero)

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There are also several major types of aquatic ecosystems in the world, which depend upon environmental factors including salinity (dissolved salt concentration), depth, and temperature. These are presented in Figure 22.6. The way we classify biomes allows us to study them, but because they are connected, molecules and energy circulate freely through different biomes.

Figure 22.6 Aquatic ecosystems are affected by salinity. (Drawing by Peter Rillero)

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review QUestions—cHaPter 22 1. Which of the following includes all of the interactions of living things with each other and with their abiotic factors? a. Ecosystem. b. Community. c. Population. d. Biotic. 2. A graph of population size versus time yields a graph that is shaped like the letter “J”. Which of the following is most likely to account for this? a. There is a successful predator feeding on the population. b. The organisms in the population are able to meet their needs and avoid predators. c. There is a limiting factor that is hindering population growth. d. The carrying capacity for this population has been exceeded. 3. Which type of symbiosis is characterized by two organisms interacting so both benefit? a. Abiotic. b. Parasitism. c. Commensalism. d. Mutualism. 4. The interactions of a species and characteristics that enhance survival help define the __________ of that species a. Niche b. Commensalism c. Succession d. Mutualism 5. Which of the following processes would have the immediate effect of removing carbon dioxide from the atmosphere? a. Combustion. b. Respiration. c. Photosynthesis. d. Symbiosis. 6. Which of the following statements is true of the carbon cycle? a. Plants use energy from the sun to produce water molecules. b. Land plants absorb and use carbon dioxide from the air. c. Oxygen is released into the air during combustion. d. As a result of respiration, the amount of CO2 in the air is decreased.

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7. Which of the following statements is true of the nitrogen cycle? a. Lightning is an important aspect because it converts unstable nitrogen into a more stable form. b. The availability of nitrogen can be a limiting factor for plant growth. c. Terrestrial plants absorb most of the nitrogen they need through their leaves. d. The amount of oxygen and carbon dioxide in the atmosphere exceeds the amount of nitrogen. 8. Which biome has abundant rainfall and is also very warm as a result of being near the equator? a. Desert. b. Tropical rain forest. c. Taiga. d. Tundra. 9. Complete the following analogy: A carnivore is to meat, as an herbivore is to __________. a. herbs b. insects c. plants d. vegetarians 10. Which type of organisms is directly responsible for bringing nitrogen from the air into the soil? a. Bacteria. b. Fungi. c. Beetles. d. Moss. (Answer Key: 1.a, 2.b, 3.d, 4.a, 5.c, 6.b, 7.b, 8.b, 9.c, 10.a)

PART VI EARTH SCIENCES

Chapter 23

PHYSICAL GEOLOGY Jeff Thomas

Mineral and rock forMation A mineral is a naturally-occurring inorganic solid that has a crystalline structure and predictable chemical composition. A rock is a combination of minerals and / or non-living organic matter. A mineral can form in thousands of ways such as by the cooling of molten materials (quartz), the evaporation of liquids (salts), and the changing of the chemical composition of rock minerals due to heat and pressure (e.g. garnets). Rocks form three ways: molten rock that cools and solidifies (igneous rocks), pre-existing eroded rocks (sediments) that are cemented and compacted together (sedimentary rocks), and preexisting rocks that change chemical composition due to extreme heat and pressure from the earth (metamorphic rocks).

identification and classification of different tyPes of Minerals, rocks and soils Minerals are identified by their physical properties that include color, streak, luster, crystalline structure, and hardness. Color is the least reliable method to identify a mineral. For instance, quartz can be white, pink, or purple. Streak is the color of the powder that is left behind when the mineral is rubbed against a harder surface. Luster is how shiny an object appears (e.g. metallic luster). Crystalline structure is the pattern or arrangement of atoms of a mineral. Basic shapes include cubic, tetragonal, orthorhombic, hexagonal, trigonal, triclinic, and monoclinic. Cleavage is how a mineral breaks which is determined by its crystalline structure. Hardness is the resistance of a mineral to being scratched. Moh’s Hardness Scale

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helps to determine the hardness of a mineral—1 is the softest (i.e. talc) and 10 is the hardest (i.e. diamond). The hardness of a mineral and how it breaks differs. For instance, glass is a hard substance, yet it breaks easily. Minerals are classified based on their chemical composition. For instance, the mineral group oxides has a chemical composition that consists of a metallic element bonded with oxygen (e.g. magnetite: Fe3O4). The most common mineral group is silicates which make up most of the earth’s surface. Examples of silicates are feldspars, quartz, and garnets. Rocks are classified by how they form. Igneous rocks are classified by how quickly the molten rock hardens into solid rock and by its chemical composition. Molten rock near or above the surface of the earth is called lava. When lava hardens, it cools quickly because it is exposed to the atmosphere and forms very small mineral crystals that are not typically visible with the naked eye. If lava cools instantly, no crystals will form and this is known as glassy texture. This type of igneous rock is classified as extrusive or volcanic. Molten rock below the surface of the earth is called magma. When magma hardens, it cools more slowly because the rock above it traps the heat (much like a lid on top of a boiling pot of water) and forms larger crystals that are visible with the naked eye. This type of igneous rock is classified as intrusive or plutonic. As for the chemical composition, there are basaltic (or mafic) and granitic (or felsic) igneous rocks. Basaltic rocks have a higher percentage of heavier elements such as iron and magnesium and have a darker color. Examples of basaltic rocks include basalt (extrusive) and gabbro (intrusive). Basalt comprises most of the bedrock on the ocean floor. Granitic rocks have a lower percentage of heavier minerals and have a lighter color. Examples of granitic rocks include granite (intrusive) and ryholite (extrusive). Granite is common on the Earth’s continents. Sedimentary rocks comprise most of the rocks on the surface of the earth and are classified by the way sediments or rock fragments form into solid rock. The two classifications of sedimentary rocks are clastic and chemical. Clastic sedimentary rocks are cemented and compacted from various sizes of rock fragments. Examples of clastic sedimentary rocks include conglomerates (from gravel), sandstone (from sand), and shale (from silt). Chemical sedimentary rocks form when dissolved minerals settle out of (or precipitate out of) solutions such as water. Examples of chemical rocks include rock salt and limestone. If the rock also has organic materials (e.g. shells, skeletal remains), then it is classified as a biochemical sedimentary rock. Examples include coal and fossil limestone. Metamorphic rocks form from preexisting rocks that change due to heat, pressure, and other chemical agents from the earth. They are classified as foliated and non-foliated rocks. Foliated rock forms as two tectonic plates collide (see Plate Tectonics) and create conditions of extreme heat and pressure. As a result, foliated rocks have large, visible crystals and have banding or layers. Examples of foliated rocks are slate (derived from shale) and gneiss (derived from granite). Metamorphic rocks that undergo less pressure and/or heat will be non-foliated.

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These rocks have no banding or layering, and have small crystals. A common non-foliated rock is marble (derived from limestone).

eartH’s layers A cross-section of the Earth is similar to that of a hard-boiled egg. The shell of an egg is similar to the crust, the white part of the egg is similar to the mantle, and the yolk of an egg is similar to the core. These layers are shown in Figure 23.1.

Crust 0-100 km thick

Man

Mantle

tle

2,900 km

re Co

km Core 5,100

er ut O

Liquid

Solid

Inne r C ore

6,378 km

Figure 23.1 Earth Layers (Drawing by Andrew Cross)

Most of our understanding of Earth’s layers comes from the study of seismic waves or earthquake waves. Seismic waves include P and S waves. P waves are longitudinal waves that travel through any material and S waves are transverse waves that only travel though solids. The crust is the solid outer-most layer of the earth and it is made mostly of granitic and basaltic rocks. Granitic rocks make up most of the continental crust while the basaltic rocks make up most of the oceanic crust. The continental crust is thicker (approximately 32km) than the oceanic crust (approximately 8km). The mantle is denser and hotter than the crust due to the increasing pressure of the earth. The thickness of this layer is approximately 2,900km. The mantle

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has a similar composition to the oceanic crust and includes elements such as magnesium, iron, aluminum, silicon, and oxygen. The upper part of the mantle and the crust is also known as the lithosphere while the lower part is referred to as the asthenosphere. The lithosphere is solid, whereas the asthenosphere is more plastic-like, due to the greater temperature and pressure. The core is made mostly of iron. The upper part of the core, called the outer core, is primarily a liquid, due to the extreme heat. The inner core is comprised of solid iron, due to the increasing pressure which changes the liquid to a solid. It is theorized that iron core produces the Earth’s magnetic field that protects us from harmful radiation from the sun. The outer core is approximately 2300 km thick while the inner core is approximately 1200 km thick.

folding, faUlting, eartHQUakes, and volcanoes Earth’s lithosphere is divided into sections known as tectonic plates (as shown in Figure 23.2). The boundaries of these plates collide, separate, or slide past one another. These plate movements cause most faults and folding of the crust as well as most earthquakes and volcanoes.

North American Plate

Eurasian Plate

Eurasian Plate Juan De Fuca Plate Philippine Plate

Caribbean Plate Cocos Plate

Pacific Plate Australian Plate

Arabian Plate

Equator

Nazca Plate

African Plate South American Plate Australian Plate

Antarctic Plate

Scotia Plate

Figure 23.2 Tectonic Plates (Drawing by Andrew Cross)

Faults are cracks in the crust and they can be found anywhere on a plate. Faults, however, are concentrated near plate boundaries. There are three types of faults: normal, thrust or reverse, and strike-slip. Normal faults occur when one block of the earth moves apart relative to the other block (as shown in Figure 23.3). In addition, the earth from one side of this fault moves downward relative

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to the other side. Normal faults are located near diverging plate boundaries (when two plates move apart). Thrust or reverse faults occur when one block of the earth collides with another block (as shown in Figure 23.3). The earth from one side of this fault moves upward relative to the other side. These kinds of faults are associated with converging plate boundaries. In some cases, folds in the crust occur along converging plate boundaries due to compressional forces as two plates collide. Strike-slip or transform faults occur when blocks of the earth slide parallel past one another (as shown in Figure 23.3).

Normal

Thrust

Strike-slip

Figure 23.3 Faults (Drawing by Andrew Cross)

Converging plate boundaries form mountain ranges, and volcanic and oceanic trenches. These landforms form when a dense oceanic plate goes underneath a less dense plate. Diverging plate boundaries mostly occur when two oceanic plates move apart. These develop mid-ocean ridges (oceanic mountain ranges) and rift valleys such as the Mid-Atlantic Ridge. Transform fault boundaries generally connect converging and diverging plate boundaries such as the San Andreas Fault. Earthquakes can occur anywhere, but they occur more frequently near plate boundaries. The magnitude of an earthquake also tends to be greater near these boundaries. For instance, the 2004 Indonesian earthquake occurred on a converging plate boundary. This was the third largest earthquake recorded. However, in 1812, a strong earthquake occurred in Missouri which is not located on a major plate boundary. The Richter Scale measures the intensity of the seismic waves. Minor earthquakes have a magnitude of 1 or 2 and major ones have a magnitude of 8 or 9. To

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determine the location of the earthquake, at least three seismic recording stations must triangulate the focus. The focus of an earthquake is where the break occurs along the fault. The epicenter is located on the surface directly above the focus (as shown in Figure 23.4)

Epicenter

Focus

Figure 23.4 Epicenter (Drawing by Andrew Cross)

The three main types of volcanoes are cinder cones, composite, and shield. Cinder cone volcanoes are explosive. They are mostly made up of cinders and tend to have steep sides that rise approximately 1000 feet. Composite volcanoes are made up of cinders and lava flows that create steep sides that rise more than 10,000 feet. These tend to be the most dangerous types of volcanoes. Shield volcanoes mainly emit lava and gases and also have elevations more than 10,000 feet. However, they have gentle slopes since the lava spreads over large areas. Most volcanoes occur when two plates collide along converging plate boundaries, or more specifically, when an oceanic plate collides with either a continental or another oceanic plate. For instance, in the Pacific Northwest, the Juan de Fuca plate collides with the North American plate forming a line of volcanoes parallel to the plate boundary. This includes volcanoes such as Mt. Rainer, Mt. St. Helens, and Mt. Shasta. Other kinds of volcanoes form due to hot spots (see Plate Tectonic Theory) such as Kilauea on the Big Island of Hawaii.

Plate tectonic tHeory The Plate Tectonic theory can help explain most geological processes such as mountain building and the rock cycle. As stated previously, the lithosphere is divided into sections known as plates. The plate tectonic theory was first conjectured by Alfred Wegener when he published The Origin of Continents and Oceans in 1915. His thesis stated that the continents where once together (known as Pangaea) and have since drifted apart. This idea was first known as “continental drift.” Evidence from his book includes the following: (a) the shapes of the continents seem to fit together (e.g. South America and Africa), (b) unique fossils found on either side of the Atlantic, (c) continental mountain ranges and rocks that

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were similar across oceans, and (d) climate evidence (e.g. tropical plants found in Greenland). Initially, his idea was rejected by the scientific community. During the mid 20th century, however, other evidence was uncovered to support his theory. For instance, mid-ocean ridges were discovered during WWII. These underwater mountains are geologically young and volcanically active. Molten rock spreads from the center of these mountains. Once the molten rock solidifies, it moves perpendicular to the spreading center at a rate between 1 to 15 cm/year. As a result, the age of the rocks progressively becomes older the further away from spreading center. This provided evidence that the plate moves. During the mid part of the 20th century, geologists noticed that most earthquake and volcanic activity occurs along narrow bands that line up with plate boundaries. Hot spots on the surface of the earth are further evidence that the plates are moving. Hot spots are stationary areas below the plates that create volcanic activity at the surface. These hot spots form chains of volcanic activity and landforms such as the Hawaiian Islands. All of this additional evidence evolved into the widely accepted Plate Tectonic Theory.

Hydrologic cycle The cyclical movement of water above, on, and below the surface of the earth is known as the hydrologic or water cycle. There are six main processes of the hydrologic cycle: (a) evaporation, (b) transpiration (c) condensation, (d) precipitation, (e) runoff, and (f) infiltration/percolation (as shown in Figure 23.5) Condensation

Water Storage in the Atmosphere

Water Storage in Ice and Snow

Precipitation

Transpiration Evaporation

Surface Runoff

Freshwater Storage

Water Storage in Oceans

Ground Water Discharge

Ground Water Infiltration

Figure 23.5 The Water Cycle (Drawing by Andrew Cross)

Snowmelt Runoff to Streams

Ground Water Discharge Ground Water Storage

Ground Water Infiltration

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Evaporation occurs when water from the oceans, lakes, and rivers changes state from a liquid to a gas (also known as water vapor) and then rises into the atmosphere. Similarly, transpiration is when water from plants evaporates into the atmosphere. As water vapor cools, it condenses to form tiny liquid water droplets which in turn form clouds. As the water droplets accumulate, collide, and become heavier, they will then fall back to the surface as precipitation. Forms of precipitation are rain, snow, sleet, and hail. Precipitation will either runoff into rivers, lakes, and oceans or infiltrate or percolate into the soil or rock. This water then becomes part of the groundwater system. This groundwater can be absorbed by plants or move into lakes or oceans.

weatHering, erosion, and dePosition Weathering is the breaking down of solid rock to form sediments by either mechanical or chemical processes. Mechanical weathering is a physical process that breaks down rocks by moving water, wind, and ice as well as the abrasion of sediments hitting one another during such processes. Chemical weathering breaks down rocks by changing their composition (oxidation/rusting). Both processes work hand-in–hand because of mechanical weathering increases the surface area available for chemical weathering to act on it. Erosion differs from weathering. Erosion is the movement of sediments due to weathering. Examples of erosion include sediments moving by a blowing wind, a flowing river, or an advancing glacier. The rates of erosion differ based on the amount of force that is transporting the sediments. Fast moving streams, for instance, will move larger-sized rocks. Fast-moving streams often occur in mountainous regions that form V-shaped valleys with steep sides. As water slows, wind subsides, and glaciers retreat, these weathered rocks stop moving and are deposited, a process is known as deposition. The factors that affect deposition include particle size, shape, density, and the velocity of the process that is moving the sediments. Deltas, low-lying areas at the mouths of rivers, form from the deposition of sediments due to the decreased velocity of the river as it enters an ocean, lake, or another river. The smallest, least dense sediments travel the furthest as the river slows. Soil is a mixture of sediments, organic matter, water, and air that can support plant growth. Soil is classified by the parent rock from which it is made and the climate of the region. Types of soil are sand, silt, clay, and loam. Sand lacks organic material and does not retain water well. As a result, this sand is not conducive for plant growth. Silt is similar to sand except the particle sizes are smaller and it retains water more readily. This results in a greater concentration of nutrients for plant growth. Clay holds water very well and the particle sizes are even smaller than silt. Although there can be greater nutrients in clay, the lack of drainage of water can also be damaging for many plants. Finally, there is loam

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which is the best soil for plants. It is comprised of many different size particles that allow the right proportion of water and nutrients for plants to grow.

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review QUestions—cHaPter 23 1. All rocks are classified by a. color. b. composition. c. formation processes. d. texture. 2. Igneous rocks that form from lava are classified as a. clastic. b. extrusive. c. foliated. d. intrusive. 3. S waves can travel through all the following layers of the earth except a. continental crust. b. oceanic crust. c. outer core. d. mantle. 4. Most active volcanoes occur a. along converging plate boundaries. b. along transform boundaries. c. randomly around the globe. d. near hot spots. 5. A ____________ plate boundary is when two plates move apart. a. converging b. diverging c. subduction d. transform 6. The main reason an ocean plate subducts underneath another plate is because of its a. density. b. magnetic polarity. c. temperature. d. velocity.

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7. Which evidence was published in The Origin of Continents and Oceans? a. Climate evidence. b. Magnetic polarities. c. Mid-ocean ridges. d. Volcanic island arcs. 8. The position on the earth’s surface directly above the source of an earthquake is called a(n) a. epicenter. b. focus. c. inertia point. d. seismic site. (Answer Key: 1.c, 2.b, 3.c, 4.a, 5.b, 6.a, 7.a, 8.a )

Chapter 24

HISTORICAL GEOLOGY

Richard Batt and Robin Harris UniforMitarianisM Historical Geology deals with the history of the Earth and its inhabitants through time. Earth’s history is recorded in the rock record, which provides the only direct scientific evidence of what happened in the geologic past. The rock record has been interpreted in different ways. Until the late 1700’s, the commonly held belief was that the Earth was only a few thousand years old, based on consideration of Biblical records. Recognition that great changes in the Earth’s surface features have taken place favored an approach to interpreting Earth history called catastrophism, with catastrophic events suggested to account for the formation of rocks and the development of landscapes. During the late 1700’s Scottish physician James Hutton developed the concept of what became known as uniformitarianism, the idea that present-day processes operated in the past and can account for what is seen in the rock record, including landscapes. Processes such as uplift, weathering, erosion, and rock formation are generally slow, but Hutton suggested that given enough time, they could cause mountains to rise up, deep canyons to be carved, and thick piles of sediments to accumulate. Because uniformitarianism involves much slower processes than catastrophism, scientists who hold this view believe the Earth may be millions of years old, rather than thousands of years. Even though most processes that account for what is seen in the rock record appear to be slow, it has been recognized that “cata-

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strophic” events have taken place in the geologic past, including flooding due to collapse of glacial ice dams that held back large lakes, major volcanic eruptions, and impacts of extraterrestrial bodies.

stratigraPHy Stratigraphy is the study of the interpretation of layered rock (both sedimentary rock and volcanic products) or sediment (including glacial deposits). Because these materials accumulate layer by layer, examination of layered sequences provides valuable clues to determining the sequence of events that took place during their formation, an important tool in relative dating. Nicolaus Steno is credited with deriving three basic principles of stratigraphy during the 16th century; these are useful in both relative age determination and correlation from place to place. The Principle of Original Horizontality states that layers are laid down horizontally, so if they are not horizontal they were since moved to their present orientation. The Principle of Superposition states that in an undisturbed sequence, the layers at the bottom are the oldest (formed first), and those at the top are the youngest. The Principle of Original Lateral Continuity states that if matching sequences are found in two different areas, such as on opposite sides of a river valley, the rocks were originally continuous all the way across before the valley was formed. These three principles, plus the Principle of Cross-Cutting Relationships developed by Hutton (a fault or igneous intrusion cutting through a rock is younger than the rock it cuts through), allow one to determine the sequence of events that took place at a given locality, as well as to correlate to other localities where the same rocks are exposed. Also important in interpreting the history of an area is the recognition of unconformities. An unconformity is a surface representing a gap in time: missing information due to either erosion of previously-deposited rocks or a time of non -deposition. There are three major types of unconformity. In a disconformity, layers of sedimentary rock were not tilted before erosion and subsequent deposition of more sediments. If sedimentary rock layers were tilted or folded before erosion, an angular unconformity is formed when deposition is renewed. A nonconformity is formed when sediment is deposited on top of eroded igneous or metamorphic rock.

relative and aBsolUte tiMe Historical Geology, like any history study, requires a consideration of time: events recorded in the rock record occurred at specific times in the geologic past. Also, because Historical Geology deals with the geological history of the planet as a whole, not only must the sequence of past events be determined for local areas, but events must be correlated (shown to be equivalent) to what took place in other areas.

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Time in Earth history can be expressed in two major ways—relative time and absolute time. Relative time is the expression of time as a comparison: older, younger, or the same age. For example, rocks collected from two separate locations may be compared to each other by determining whether those from one formed before (are older than) those from the other. In contrast, absolute time refers to the actual age of a rock, or the actual time an event took place, expressed in years before the present.

fossil record and forMation The study of life of the geologic past is Paleontology, and fossils are the preserved evidence of this life. Fossils may represent either the remains of organisms (body fossils) or evidence of the activity of organisms (trace fossils). Body fossils often represent more durable parts, such as bone or shell, while burrows, trails, and footprints are examples of trace fossils. In order for any part of an organism to be preserved, the remains need to be buried. Because natural burial is most common beneath sediments, fossils are usually associated with sedimentary rock. After burial, organic matter (“soft parts”—tissues and organic skeletal structures) usually decay, while structures impregnated with minerals (“hard parts”—mineralized skeletons), have the best chance to be preserved as a fossil. Organic body parts may be preserved under unusual circumstances. Burial of organisms in anoxic (lacking dissolved oxygen) water prevents decay, but pressure from overlying sediments eventually converts the remains to carbonized films that preserve the details of the organism (carbonization). Organic material may also be preserved by some other means that prevents decay, such as encasing in amber, burial in a highly saline environment, or freezing. Skeletal structures may be preserved in a variety of ways. Mineralized skeletons may remain intact (preservation of original material). Porous structures, especially bone or wood, may become impregnated with minerals that fill each space to create a fossil showing the original microscopic detail (permineralization). Water percolating through sediments may dissolve away buried hard parts while at the same time ions precipitate out in their place as a different mineral (replacement). If sediment becomes cohesive before breakdown of buried skeletal material a hollow cavity, or mold, is left behind that preserves the detail on the outer surface of the skeleton. This mold may later become filled in with minerals, creating a cast. If a buried shell becomes filled before the shell itself dissolves away, an internal mold develops as the surface of the in-filling material preserves details of the inside of the shell. Because burial that is so vital to the preservation of the remains of organisms is sporadic (flooded rivers depositing mud on floodplains, influx of sediment into a sea, ash-fall from volcanic eruptions), and because even after burial remains

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may still break down without leaving a trace, the fossil record provides us with only a very small sample of what organisms lived in the geologic past. The record is biased toward species that had hard parts, and also toward environments in which sediments were likely to be deposited and not eroded away later.

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review QUestions—cHaPter 24 1. According to the concept of uniformitarianism, which of the following is not true? a. Catastrophic events have shaped most of the Earth’s surface. b. The rock record is based on processes that generally have not changed over time. c. It has taken a great deal of time for the Earth’s current landscape to develop. d. Processes such as erosion and mountain building have always occurred very slowly. 2. Stratigraphy involves which of the following? a. An examination of how heat and pressure may have shaped the Earth’s surface. b. A study of the fossil record to trace the development of Earth’s history. c. Examination of sedimentary rock sequences to determine the order of events that took place in their formation. d. An analysis of how heat and pressure affect rock formation. 3. Which of the following would be an example of relative time? a. Determining that a rock is older since it was found near the bottom of a sequence. b. Using radiometric dating methods to determine the age of a rock. c. Stating that a rock is approximately 12,000 years old. d. Examining the chemical composition of a rock sample. 4. Which type of fossil forms when a hollow cavity that is left behind by dissolving skeletal material is later filled with minerals? a. A mold fossil. b. A cast fossil. c. A soft fossil. d. A preserved fossil. (Answer Key: 1.a, 2.c, 3.a, 4.b,)

Chapter 25

OCEANOGRAPHY Jay Hunt

geograPHic location of tHe oceans and seas There are five world oceans—the Pacific, the Atlantic, the Indian, Southern (or Antarctic), and the Arctic. The Pacific Ocean is the largest (over 156 million square km, about 33% of the earth’s entire surface) and deepest (average depth over 4,028 meters). The Arctic is the smallest (about 14 million square km) and shallowest (average depth about 1,205 meters).

tHe Pacific ocean

The Pacific is the world’s largest ocean. It is bounded on the north by the Arctic Ocean, on the west by Asia and Australia, on the east by North and South America, and on the south by the Southern Ocean (at 60° S latitude). It covers 1/3 of the earth’s surface and includes the deepest ocean location on earth, the Mariana Trench (10,923 meters). The equator is sometimes used to divide the ocean into a North Pacific Ocean and a South Pacific Ocean.

tHe atlantic ocean

The Atlantic is the world’s second largest ocean. It is bounded on the north by the Arctic Ocean, on the west by North and South America, on the east by Europe and Africa, and on the south by the Southern Ocean (at 60° S latitude). It is about 77 million square km in size (about 16% of the earth’s surface) and has an average depth of 3,926 meters. The equator is sometimes used to divide the ocean into a North Atlantic Ocean and a South Atlantic Ocean.

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tHe indian ocean

The Indian is world’s third largest ocean, although it is only slightly smaller than the Atlantic, covering 69 million square km. It is bounded on the north by Asia, on the west by Africa, on the east by Australia, and on the south by the Southern Ocean (at 60° S latitude). It has an average depth of 3,963 meters.

tHe soUtHern ocean

The Southern Ocean was delineated by the International Hydrographic Organization in the Spring of 2000. It covers 20 million square km, making it similar in size to the Arctic Ocean. Although there are some authors who still resist recognizing the Southern as a fifth ocean (extending the southern border of the Atlantic, Pacific, and Indian oceans to the continent of Antarctica), most oceanographers now recognize the Southern Ocean due to its unique nature. It is bounded on the south by Antarctica, but it has no east or west boundary. This is because the Antarctic Circumpolar Current is the only major ocean surface current not impeded by land as it circles the globe. It is this current that influences the northern boundary of the Southern Ocean, which was set by the IHO at 60° South latitude.

tHe arctic ocean

The Arctic is the world’s smallest ocean and its most shallow, covering only 3% of the earth’s surface. It is unique among earth’s oceans as being mostly covered by ice for much of the year. It is also unusual in the amount of land that borders it. It is virtually surrounded by the northern extents of Eurasia and North America. There is a small connection to the Pacific Ocean through the Bering Straight, and several broader connections with the Atlantic.

forMation and MoveMent of ocean waves The interaction of the surface of the ocean with winds in the atmosphere is responsible for generating ocean surface waves. The size of waves is related to factors including wind speed and duration, fetch (the distance over which wind blows) and water depth. The nature of any wave is to transmit energy (the wave) without much (or any) translocation of mass. For example, a wave may travel across an entire ocean, but as a wave passes any given point, the water molecules move in circles and essentially do not travel with the wave. Waves that continue to travel without the winds that originally created them are called swells. Waves interfere with each other by combining to form larger waves (constructive interference), smaller waves (destructive interference), or more typically a combination of the two (mixed interference). These complicated mixed waves represent what most people associate with the open ocean surface.

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anatoMy of a wave

The orbital motion of water particles makes them rise to the peak of the circle, called the wave crest, and fall again to the base of the circle, called the wave trough (see Figure 25.1). The vertical distance between the crest and the trough is called the wave height, while the distance between two sequential crests (or troughs) is called the wavelength. The orbital motion of water particles decreases with depth, until the wave energy is negligible. This occurs at approximately ½ of the wavelength and is called the wave base. This means that the energy of a wave will not have any influence in water deeper than the wave base. Therefore, when a wave approaches the shore and the wave base reaches the seafloor, it will disturb the seafloor and begin to be influenced by it. Wave height will begin to increase as water is pushed upwards. The wave will eventually break as the crests spill over and cascade downward in the familiar line of “breakers” that occurs near the seashore. This typically happens when the wave height is about 1/7 of the wavelength (wave height/wavelength is called wave steepness).

Figure 25.1 Anatomy of a Wave (Drawing by Jay Hunt)

tides A tide is a special kind of wave that has a wavelength that spans thousands of miles and is strongly influenced by the moon. It is a common misconception to view the moon as revolving around a static earth. Rather, the earth and moon each revolve around their common center of mass (barycenter). Two tidal bulges (crests of the wave) typically occur on earth at any given time, one facing the moon and one facing away from the moon. The bulges result from the interaction of lunar gravity and centripetal forces generated by the entire system. In many places, the two bulges result in semi-diurnal tides, two high tides (and two low tides) occurring during a lunar day (about 24 h 50 min). However, diurnal tides (one high tide per lunar day) and mixed tides (more variable high and low tides) can also occur due to other factors including topography and the interference patterns of the tide

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waves themselves (note: tides are not related to tidal waves (tsunamis), which are typically generated by tectonic events). Although tides are heavily influenced by lunar gravity, there are many other influences as well, including interference from other tides, regional topography, and the sun’s gravity. When the gravity of the sun and the moon act together on the earth, the high tides are highest and the low tides are lowest. These are called the spring tides, and they occur when the moon is full or new. When the gravity of the sun and the moon act in opposition to each other (i.e. the sun and moon are at roughly 90° angles from each other with respect to the earth, such as when the moon is in 1st or 3rd quarter), the high tides are not so high and the low tides are not so low. These are called neap tides.

sUrface and deeP-water cUrrents While ocean surface currents tend to travel in the same general direction as surface winds, their path is deflected by Coriolis Forces. The result of Coriolis Forces tends to move ocean surface currents toward the right in the northern hemisphere (clockwise in major ocean centers or gyres) and to the left in the southern hemisphere (counterclockwise in major ocean gyres). Deep-water currents are driven primarily by thermodynamic properties in the world’s oceans. As heat is transported from surface waters at the equator towards the poles, it begins to cool. The cold, saline water near the poles is generally the densest oceanic surface water on the planet, with water near Antarctica slightly denser than near the Arctic. These water masses sink to the seafloor and travel back toward the equator and beyond along the seafloor, until they begin to rise back toward the surface. In this way, heat is transferred from the equator to higher latitudes, bringing a moderate climate to many areas of the planet that would otherwise be very cold (e.g. northwestern Europe). This Global Ocean Conveyor, as it has been described, is critical for explaining why liquid water occurs over most of the latitudes of our planet, and it is an example of how the oceans regulate the temperature on earth, making it more suitable for life as we know it.

toPograPHy and landforMs of tHe ocean floor and sHorelines The area along the shore that occurs between low tide and high tide is called the intertidal (or littoral) zone. Below the low tide, the seafloor gradually deepens along a relatively shallow underwater ledge, called the continental shelf. The shelf is narrow near active tectonic regions (active continental margins) and broader in non-tectonic regions (passive continental margins). The shelf extends to the continental shelf break, an area where the slope of the seafloor increases. The break marks the boundary between the continental shelf and the continental slope. Sediments that accumulate near the bottom of the slope are known as the continental rise, and these in turn lead to vast expanses of flat seafloor called the

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abyssal plains (so called because they are typically at depths greater than 4,000 meters). The abyssal plains are occasionally broken by deep, narrow canyons called trenches. Trenches are usually deeper than 6,000 meters and the deepest (the Mariana Trench) is nearly 11,000 meters deep.

seafloor featUres

The ocean floor has huge mountain ranges and extensive canyon and valley systems, just as we find on land. Underwater mountains, or seamounts, can sometimes grow tall enough from volcanic activities to break through the sea surface and become islands, such as the Hawaiian Island chain. In fact, if mountain height were measured from the seafloor, Mauna Kea in Hawaii would be the tallest mountain in the world, far taller than Mount Everest. Underwater seamounts provide refuge for many species to gather in the open ocean. They force cold, nutrient rich, water from the deep upward nearer the surface, creating opportunities for plankton to thrive and, in turn, the animals that feed on them. Sometimes, a mountain chain can be created by the separation of two oceanic plates. Such Mid-ocean Ridges are common in most of the world’s oceans. The Mid-Atlantic Ridge runs north to south, along the midline of the entire Atlantic Ocean, making it the longest (and one of the largest) mountain chains in the world. Sometimes mountains are created when earth plates collide, such as the Rocky Mountains and Andes Mountains of North and South America. But when such a mountain chain is separated from the mainland by a sea, the chain is called an Island Arc. The islands of Japan are a good example of an island arc, separated from Asia by the Sea of Japan.

PHysical and cHeMical ProPerties of seawater and nUtrient cycles of tHe ocean There are many physical and chemical properties of seawater that are important in oceanography. Ocean water is salty and has many elements dissolved in it. The abundance of these dissolved ions is relatively similar across much of the world’s oceans. This is called the rule of constant proportions.

teMPeratUre

In the deep sea, the temperature is consistently cold. Below 1,000 meters, the temperature varies between 2°C and 4°C. From 1,000 meters up to the surface, sea temperature rises gradually except for a rapid change in temperature over a short change in depth called the thermocline. The thermocline can be relatively shallow near the equator (about 50 meters), getting gradually deeper and less pronounced at higher latitudes, until it eventually disappears near the poles as uniformly cold water extends from the deep to the surface. In fact, surface polar waters will ultimately get colder than the waters below and sink to the seafloor, driving deep-ocean circulation patterns.

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salinity

The salinity of seawater is defined as the total number of particles by weight dissolved into water. Traditionally, this is defined in parts per thousands (ppt). Full oceanic seawater is about 35 ppt. Therefore, about 35 grams of salts are dissolved in 1000 g of seawater (1 kg, or 1 liter). The major particles, or solutes, dissolved in seawater are relatively constant across the oceans. The two most important are sodium (Na+) and chloride (Cl-), which comprise almost 86% of ocean salts. Magnesium (Mg2+) and sulfate (SO4)2- make over 11%, with calcium (Ca2+) and potassium (K+) each contributing over 1% of the remainder. Taken together, these six major ions account for more than 99% of salts in the oceans. Virtually every known naturally occurring element can be found in trace amounts in the seawater, and contributes to the tiny remaining fraction of ocean salts.

density

The density of seawater increases with salinity and as the water gets colder. Seawater density is usually expressed in g/ml or some equivalent (Kg/m3). The average density of seawater is about 1.025 g/ml, with a range from about 1.020 to 1.030 covering most of the world’s oceans. As expected, density tends to be less on the surface and increases with depth. Like temperature, there is a rapid change in density associated with a relatively small change in depth in the upper 1,000 meters, called a pycnocline. Since salinity in a given area of the ocean does not vary much, the pycnocline often appears as a mirror image of the thermocline in a depth profile.

PressUre

Air surface pressure at sea level is defined traditionally as 1 atmosphere (1 ATM, or 760 mmHg) under standard conditions. Pressure increases with water depth by about 1 ATM for every 10 meters. For comparison, the pressure change in the atmosphere that occurs between the top of Mount Everest and sea level is equivalent to the change in water from the surface to about 20 meters in depth. Since the average depth of the oceans is nearly 4,000 meters, the enormous pressures in the deep sea have a considerable impact on the biology and ecology of animals that live there. Indeed, the pressures are so great in the deepest oceans that many physical, chemical, and geologic processes are different than on land. For example, water temperature near deep-sea hydrothermal vents frequently exceeds 350°C without boiling, due to the high pressures.

ligHt

Most of the world’s oceans are completely devoid of sunlight. In general, organisms that undergo photosynthesis are restricted to the upper 200 meters of the ocean. Furthermore, different colors of light travel different distances in water. Red light travels the least, with purple and orange disappearing next, followed by yellow, green, and finally blue. In the deep sea, where sunlight is absent, most

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species are bioluminescent, producing their own light. Bioluminescent light is typically blue in order to travel the farthest in water, although there are rare exceptions.

nUtrient cycles

Living organisms require energy to grow and reproduce. Organisms can either acquire energy by ingesting other organisms (animals and zooplankton) or making their own through photosynthesis (plants and phytoplankton). Ultimately, nutritive energy comes from organic carbon compounds like the sugar glucose produced during photosynthesis. The process takes in carbon dioxide and water and, in the presence of sufficient light, produces glucose and oxygen. Carbon is therefore an essential nutrient for biological systems. But it is important to remember that plants and phytoplankton also need other elements in order to be healthy and undergo photosynthesis. For example, nitrogen is essential for building chlorophyll, while phosphorus is necessary for building many molecules used in the chemical pathway of photosynthesis. There are many other nutrients necessary for photosynthesis, but nitrogen and phosphorus are often in limited supply in seawater. Carbon, nitrogen, and phosphorus originate from the elemental earth and the atmosphere. Therefore an understanding of how these elements are introduced and recycled through biological systems is important.

tHe carBon cycle

In order to be useful to living organisms, carbon in CO2 must be converted into the simple sugar glucose. When CO2 in the atmosphere mixes with water, it becomes available to plants and phytoplankton for photosynthesis. The carbon is converted to glucose, or fixed through a process called primary production. Carbon in glucose is then passed up the food chain to animals through feeding. Some CO2 is returned to the sea by the respiration of plants and phytoplankton. Animals also pass carbon back to the sea through respiration. When any living organism dies, it decays and becomes detritus (pieces of dead organic matter), and eventually dissolves completely into seawater (called dissolved organic matter or DOM). Carbon is returned to the seawater in this way as well. Additionally, animals, plants, and phytoplankton return some carbon back to the environment through excretion while alive. Some animals also feed directly on detritus and can recycle carbon this way. The carbon cycle is also tied to rocks and sediments. This is because when CO2 mixes with water, it becomes carbonic acid and the bicarbonate ion (HCO3)-. The bicarbonate ion can be combined with calcium to create calcium carbonate (CaCO3) and other related materials, which are used by many organisms for hard parts such as shells and bones. These hard parts sink to the seafloor after death and become part of the sediment, or given enough time, rocks such as limestone.

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tHe nitrogen cycle

Nitrogen occurs naturally as a gas (N2) in our atmosphere. It cannot be used in this form by living organisms, except by some bacteria (e.g. cyanobacteria), which have the ability to convert it to nitrate (NO3)-, the biologically useful form of nitrogen. Nitrogen gas from the atmosphere dissolves into water and is converted by bacteria into nitrate, which is absorbed by plants and phytoplankton, although a little is returned by excretion. Nitrogen is passed up the food chain through feeding as with carbon, and is returned to the environment through death and decomposition, as with carbon.

tHe PHosPHorUs cycle

Phosphorus enters the oceans mostly through the weathering of terrestrial rocks, with a small amount from the atmosphere. It enters in the form of phosphate (PO4)3-, which is the biologically useful form. Phosphates are absorbed by plants and phytoplankton, although a little is returned to seawater by excretion. Phosphate is passed up the food chain through feeding as with carbon and nitrogen, and is returned to the environment through death and decomposition, as with carbon and nitrogen.

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review QUestions—cHaPter 25 1. Which ocean is the smallest and shallowest? a. The Arctic. b. The Atlantic. c. The Indian. d. The Pacific. e. The Southern. 2. Which ocean was recently described? a. The Arctic. b. The Atlantic. c. The Indian. d. The Pacific. e. The Southern. 3. When two waves combine in such a way as to create a larger wave, this is called a. constructive interference. b. destructive interference. c. mixed interference. d. fetch. e. none of the above 4. The distance between two successive wave crests is called the a. wave height. b. wave steepness. c. wavelength. d. wave base. e. fetch. 5. Tides are influenced by a. the gravity of the moon. b. the gravity of the sun. c. interference from other tides. d. regional topography. e. all of the above.

Oceanography

6. The relatively shallow underwater ledge near shorelines is called the a. Continental Rise. b. Continental Shelf. c. Continental Slope. d. Continental Shelf Break. e. Abyssal Plains. 7. The average amount of salts dissolve in 1 liter of seawater is about a. 1 gram. b. 2 grams. c. 10 grams. d. 15 grams. e. 35 grams. 8. A relatively rapid change in density with small change in depth is called a. a thermocline. b. a pycnocline. c. the shelf break. d. an ocean conveyor. e. none of the above. 9. The color of light that travels farthest in water is a. red. b. yellow. c. green. d. blue. e. purple. 10. In order to undergo photosynthesis, phytoplankton and plants need a. carbon dioxide. b. water. c. nitrogen. d. phosphorous. e. all of the above. (Answer Key: 1.a, 2.e, 3.a, 4.c, 5.e, 6.b, 7.e, 8.b, 9.d, 10.e)

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Chapter 26

METEOROLOGY Robert Cohen

atMosPHeric layers Except for clouds and precipitation, which consist of solid or liquid water, the atmosphere is made up of gases that are invisible for the most part. We know the gases are there because of two quantities, pressure and temperature. Thus, it should not be too surprising that we measure the atmosphere in terms of pressure and temperature. The pressure is greatest near the surface of the Earth and decreases as you move up in the atmosphere. Unlike air pressure, the air temperature is not necessarily cooler or warmer at higher altitudes. During the day, the temperature near the Earth’s surface may be significantly warmer than the air above it. At night, on the other hand, the temperature near the Earth’s surface may be cooler than the air above it. However, there are some general features of the air temperature that we can describe in terms of an average atmosphere. We’ll focus on the atmosphere between the surface and 85 km high (about 53 miles). At an altitude of 85 km, over 99.99% of the atmosphere would be below you (i.e., at that altitude the sky would appear black instead of blue). The average atmosphere can be broken into four layers, based upon the temperature. Suppose you ascend upward through the atmosphere (in a balloon, for example). As you ascend, you’d find that the temperature would alternate between cooling with height and warming with height (as shown in Figure 26.1).

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Figure 26.1 Temperature (°C; horizontal axis) with height (km; vertical axis); for comparison, Mt. Everest is around 9 km high (Drawing by Robert Cohen)

First, you’ll find that the temperature decreases as you ascend, reaching a chilly –57°C (–70°F) at a height of around 11 km or so (about 7 miles; clouds tend to be restricted to this layer). We call this region the troposphere (“tropo” comes from the word for “mixing,” which is what produces the clouds). The reason the atmosphere is warmer near the surface is because the atmosphere is mostly transparent to the solar radiation associated with the sun’s rays. The solar radiation is able to pass through the atmosphere until it reaches the Earth’s surface, at which point the radiation is absorbed and the Earth’s surface warms up, subsequently warming the air near it while the air above it stays cool. However, as you continue to ascend in the balloon, you’ll find that the temperature no longer gets colder with height. Instead, the temperature remains pretty much the same until you reach a height of around 20 km (12.4 mi) at which point it gets warmer and warmer as you ascend, reaching –2.5°C (27°F) at a height of 48-51 km (30-32 miles). We call this region the stratosphere (“strato” comes from the word for layered, which is the opposite of mixing). The air temperature then cools with height, reaching –86°C (–123°F) at 8691 km (53-56 mi), before warming again. The top layer, the one that warms with height, is called the thermosphere (“thermo” because it is warm) while the one below it is called the mesosphere (“meso” because it is in the middle). It is important to note that we use a similar terminology to refer to the zone between each layer. The tropopause is the region where the atmosphere transitions from the troposphere to the stratosphere, the stratopause is the region where the

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atmosphere transitions from the stratosphere to the mesosphere, and the mesopause is the region where the atmosphere transitions from the mesosphere to the thermosphere. The reason it is warm at a height of 48-51 km and warm at heights greater than 91 km is the same reason it is warm at the Earth’s surface—solar radiation is being absorbed. The air molecules at the top of the atmosphere, being the first to encounter the sun’s rays, will absorb more than the molecules below them. Then, at a height of 48-51 km, the solar radiation is absorbed by a gas called ozone that is particularly good at absorbing radiation in the ultraviolet region of the sun’s radiation. It is a good thing the ultraviolet radiation is absorbed prior to reaching the Earth’s surface, as ultraviolet radiation causes sun burn and skin cancer. Please note that there are other ways of classifying the structure of the atmosphere. This classification scheme uses temperature. Other classification schemes might use composition or electrical properties. It is common, for example, to add an additional layer, the exosphere, which corresponds to the transition between the thermosphere and space.

cHeMical coMPosition of tHe atMosPHere As mentioned in the previous section, the atmosphere is made of gas molecules. Almost all of the molecules are nitrogen. You probably already know that some of the molecules are oxygen, since we breathe oxygen. However, most of the molecules are nitrogen, with oxygen only making up about one-fifth of the molecules. Pollutants make up only a tiny fraction of the atmosphere, but they can have a significant impact on our life. For example, carbon dioxide makes up around 0.04% of the atmosphere, yet its steady increase is a major contributor to global warming. Ozone makes up an even smaller fraction of the atmosphere, yet it only needs to be 0.000008% of the air in order to be unhealthy for sensitive people.

seasonal, latitUdinal and daily variation of solar radiation latitUdinal variation of solar radiation

As mentioned in the first section, the Earth’s surface absorbs solar radiation, and this warms its surface. One might think that the equator is warmer because it is closer to the sun than the Earth’s poles. However, the difference in distance is very small compared to how far away the sun is from the Earth. As such, the impact of the distance on the surface temperature is miniscule. Rather, the orientation of the surface is the main reason why the Earth’s equator tends to get warmer than the poles. When the surface is oriented perpendicular to the sun’s rays, as the ground at the equator tends to be, it will intercept (and thus absorb) more solar radiation than if it is oriented parallel to the sun’s rays (as shown in Figure 26.2).

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Figure 26.2 Earth’s surface around the equator is oriented perpendicular to sun’s rays. Around the poles, the surface is parallel to sun’s rays. (Drawing by Robert Cohen)

seasonal variation of solar radiation

Since the Earth’s axis of rotation is tilted relative to its orbital plane, the area of the Earth that intercepts the most solar radiation periodically alternates between the northern hemisphere and the southern hemisphere (as shown in Figure 26.3), leading to seasons that are warmer (summer) and cooler (winter).

Figure 26.3 Orientation of Earth during different seasons (Drawing by Robert Cohen)

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daily variation of solar radiation

The air near the surface warms up during the day because the surface absorbs solar radiation. The air near the surface cools down at night because the surface gives off radiation (infrared, not visible). One factor that impacts how much the air near the surface cools off during the night is the presence of water vapor and clouds. Water vapor is a strong absorber of infrared radiation (carbon dioxide also absorbs infrared radiation, but less so). This is why the air temperature at night does not cool as much when the sky is cloudy or the air is humid. Without these gases (called greenhouse gases), more radiation would make it through the atmosphere and the surface would cool so much that the average temperature at the surface would only be about –18°C (0°F).

gloBal wind Belts By convention, the Earth’s equator is at latitude zero degrees and the poles are at latitude 90 degrees. Locations within 30 degrees of the equator (i.e., between 30°N and 30°S) are known as the tropics and locations between 30 and 60 degrees are known as the mid-latitudes. As shown in Figure 26.4, the wind tends to come from the west in the midlatitudes, where most of the world’s population lives. This is not to say that the wind is always from the west because it isn’t. However, it is from the west more than it would be if the wind direction were totally random.

Figure 26.4 Illustration of global wind belts (Drawing by Robert Cohen)

The tendency of the wind to come from the west is known as the mid-latitude westerlies. It is more pronounced at the tropopause than at the surface. In fact, the wind near the tropopause can be quite fast, which leads to significantly less

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flight times for airplane flights traveling eastward versus westward. Such highspeed winds in the mid-latitudes are typically restricted to a band known as the jet stream. Outside of the mid-latitudes, we tend to observe winds from the reverse direction (i.e., from the east). Poleward of 60°N and 60°S we call them the polar easterlies and in the tropics they are known as the trade winds. Between the westerlies in the mid-latitudes and the easterlies in the tropics is a region of relatively calm winds known as the doldrums. At the equator, nestled between the trade winds on either side of the equator, lies the intertropical convergence zone (ITCZ).

sMall-scale atMosPHeric circUlation At any given time, the wind direction may not correspond to the directions described in the previous section. This is because the air in the atmosphere is constantly changing. Just as water on a stove continually mixes, so does the air in the atmosphere. How quickly it changes depends on what we are looking at. For example, if you took a satellite picture of the Earth, the clouds would look pretty similar from one minute to the next. Only when comparing pictures taken over several hours would you start to see a difference. In comparison, if you took a picture of the smoke coming out of a chimney, you’d easily see differences between pictures taken only seconds apart. The tendency is that larger circulations evolve over longer time periods. Small circulations, like that associated with the motion of chimney exhaust or the movement of leaves, have life cycles on the order of seconds or minutes. Such circulations are called microscale circulations. Larger circulations, like those associated with the global wind patterns discussed in the previous section , have life cycles on the order of days or weeks. In between these two extremes, there are mesoscale circulations and synoptic scale circulations. Both describe weather circulations with synoptic scale circulations being larger, like those associated with high and low pressure systems, and mesoscale circulations being smaller, like those associated with thunderstorms and tornadoes. Mesoscale circulations (so named because “meso” means “middle”) have life cycles on the order of hours whereas synoptic scale circulations have life cycles on the order of days. The word synoptic means “one view” and refers to the size of the circulations depicted on the standard weather observation maps (where observations from a single time are plotted).

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ways to indicate tHe MoistUre content of tHe air sPecific HUMidity

As mentioned previously, between 1-4% of the atmosphere is water vapor. This fraction is known as the specific humidity. Though it can be reported as a percentage, it is usually measured in terms of grams of water vapor per kilograms of air (e.g., 15 g/kg).

aBsolUte HUMidity (water vaPor density)

Another way to indicate the water vapor content is the absolute humidity (or water vapor density), which is the mass of water vapor per volume. A typical absolute humidity is around 0.01 kg / m3, or about one-hundredth of the density of air (the density of air is about a thousand times smaller than the density of liquid water).

relative HUMidity

It is more common to use relative humidity to describe how much water vapor is present because relative humidity indicates how close we are to the point where the water vapor will start to condense. That point is called saturation. At saturation, we say the relative humidity is 100%. Any additional water vapor will condense to form liquid water droplets. Unlike specific humidity and absolute humidity, the relative humidity does not tell us how much water vapor is present. It only tells us how close we are to saturation. Since it is easier for water to condense when the water vapor is cooler, less water vapor is needed to produce saturation at lower temperatures.

dew Point and frost Point

While it is possible to reach saturation (100% relative humidity) by evaporating water, the more common method is by cooling the air. By cooling the air, less water vapor is needed for saturation. Once saturation is reached (100% relative humidity), further cooling results in condensation and dew forms. For this reason, this temperature is called the dew point (or the frost point if that temperature is below freezing).

cloUd and PreciPitation tyPes PreciPitation tyPes

When the temperature falls to the dew point, some water vapor condenses to form droplets. If the air is near Earth’s surface, the droplets form on surfaces. If the air is above the Earth’s surface, there is no surface to condense onto and so the droplets form on tiny little particles called cloud condensation nuclei. The result is a cloud full of droplets. When cloud droplets get big enough, they fall as rain. Rain is one type of precipitation, which is water that falls to the ground. If the

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temperature is cold enough, ice crystals are formed instead of water droplets. When the ice crystals get big enough, they fall as snow. Usually, air is colder the higher one goes in the troposphere, so unless it is colder throughout the troposphere (as in winter), the ice crystals will melt before hitting the ground, at which point they will fall as rain. Sometimes, however, the air is cooler just above the ground than higher up. In those cases, the raindrops can freeze upon hitting the ground. We call that freezing rain. If the raindrops freeze into tiny little balls of ice prior to hitting the ground, we call that sleet or ice pellets. Larger balls of ice, called hail, can fall from the sky. Hail forms when updrafts push raindrops up into regions where the temperature is below freezing, causing the raindrops to freeze. With a strong enough updraft, the ice pellet can be pushed into the freezing region multiple times, growing bigger each time. The hailstone falls to the ground when either the updraft diminishes or the hailstone grows big enough that the updraft is not sufficient to keep it aloft.

cloUd tyPes

Cloud droplets or ice crystals form when the air is cooled, and air cools when it rises. The greater the rising, the more cooling that occurs. For this reason, thunderstorms and intense rain are associated with deep clouds that extend through a large depth of the troposphere. In comparison, shallower clouds may bring only light precipitation or none at all. A common cloud classification scheme uses Latin words. For example, the small fluffy clouds typically seen during fair weather are called cumulus clouds because “cumulus” means “heap” or “pile” in Latin. Prior to rain, one might see an increase in very high feathery-like clouds called cirrus clouds, where “cirrus” means “curl” in Latin (as in a “curl of hair”). As the rain gets closer, the clouds may appear as one layer covering the whole sky. Such clouds are called stratus clouds, where “stratus” means “spreading” in Latin. Finally, the rain comes, and we call those nimbostratus clouds or cumulonimbus clouds, where “nimbus” means “cloud” or “mist” (from the same Latin root as the word “nebula”). There are many more variations on these names as well.

Major tyPes of air Masses Suppose you wanted to forecast the temperature for tomorrow. One way to do this would be to first identify the wind direction. How does this help? If the air is coming from a region that is hot and muggy, chances are tomorrow will likewise be hot and muggy. On the other hand, if the air is coming from a region that is cold and dry, chances are tomorrow will be cold and dry. This is because it takes time to change the characteristics of a large volume of air. So, if the air is hot and muggy, chances are that air will still be hot and muggy tomorrow.

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Regions of air that have similar characteristics of temperature and moisture are called air masses. We tend to name air masses based upon their temperature and moisture characteristics. Consequently the names are combinations of two words. The first word is either maritime or continental. Maritime air masses come from over the ocean and, as such, are moist. Continental air masses come from over the land and, as such, are dry. The second word is either polar or tropical. Polar air masses come from regions closer to the pole and, as such, are cold. Tropical air masses come from regions closer to the tropics and, as such, are warm. Consequently, air masses tend to be grouped into the following four types: continental polar (dry and cold), maritime polar (cold and damp), continental tropical (dry and warm) and maritime tropical (warm and muggy).

low- and HigH-PressUre systeMs PressUre differences and wind

Whereas the air pressure decreases as one ascends in the atmosphere, at a single altitude the air pressure is roughly the same all around the Earth. Still, there are slight differences in air pressure even at the same altitude (the differences are about 2-3% of the air pressure). These slight differences result in wind as higher pressure air pushes into regions of lower pressure air. For example, at the surface a difference in pressure of only 1% over a distance the length of Pennsylvania would be sufficient to produce a wind speed of several hundred miles per hour!

low-PressUre systeMs

As higher pressure air converges into a region of lower pressure air, something strange happens. The air circulates around the lower pressure air, rather than converging directly into it. The circulation has to do with the rotation of the Earth. The Earth, along with all of us and the atmosphere, is rotating about its axis. This rotation is very slow (twice as slow as the hour hand on a clock), too slow for us to notice, but it is there nonetheless. Just as a skater spins faster when the skater’s arms are brought toward the chest, the air spins faster when it converges inward toward the low pressure center. The direction of circulation is the same as the Earth’s rotation, which appears to be counter-clockwise when looking down upon the northern hemisphere (as shown in Figure 26.5). Meteorologists call all such circulating low pressure systems cyclones. Note that many people associate the word “cyclone” only with tropical cyclones or tornadoes, the latter of which are very intense low pressure circulations.

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Figure 26.5 Spinning of low-pressure systems like hurricanes vs. spinning of Earth (Drawing by Robert Cohen)

HigH-PressUre systeMs

High pressure systems are sort of the reverse of a low pressure system. Since air is forced from high to low pressure, air diverges away from a high pressure system. Just like a skater whose rotation rate slows when the arms are pushed away from the chest, high pressure systems rotate slower than the Earth. In the northern hemisphere, which appears to rotate counter-clockwise (by an observer looking down on the Earth), that slower rotation will appear as a clockwise rotation of wind.

frontal systeMs The circulation around a low pressure center tends to produce precipitation and storms. To understand why, consider that in the northern hemisphere, air tends to circulate counter-clockwise around a low pressure center. This means that warm air is pushed northward east of the low pressure center. As the warm air gets pushed northward, it encounters colder air. The boundary between the approaching warm air and the cold air, like approaching infantry in a battle, is called a warm front. A warm front is illustrated on a weather map by a line with semicircles (see far northeast United States in Figure 26.6). West of the low pressure center, cold air is pushed southward. The cooler air tends to be associated with clearing skies. However, just as there is a warm front where the warm air approaches the colder air east of the low pressure center, there is a cold front where the cold air west of the low is pushed into warmer air further south. A cold front is illustrated on a weather map by a line with triangles (see Great Lakes and mid-Atlantic regions in Figure 26.6). Along the fronts, both warm and cold, clouds and precipitation form as the warm air is pushed upward and cools. Clouds and precipitation tend to be different along a cold front than along a warm front, however. Along a warm front, the

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clouds and precipitation tend to cover a larger area and the precipitation is not as intense as along a cold front.

Figure 26.6 Map with fronts (Drawing by Robert Cohen)

interPretation of weatHer MaPs When people refer to a weather map, they frequently mean a synoptic map like the one shown in Figure 26.6. The center of the high and low pressure systems are designated by H’s and L’s, respectively. Cold fronts and warm fronts are indicated by lines with triangles and semicircles, as discussed in the previous section. The map may also include lines for stationary fronts, which are boundaries between the warm and cold air that are neither moving into the warm air nor moving into the cold air (indicated by lines with triangles on cold side and semicircles on the warm side, as in the northern plains in Figure 26.6). There are also boundaries across which there is no temperature contrast. Troughs (wind shifts but no temperature difference) and dry lines (dry air moving into moist air) are indicated by dashed black lines (see southwest United States in Figure 26.6). An occluded front is somewhat like a trough and a dry line, with dry cold air moving into moist cold air (indicated by lines with triangles and semicircles on the same side, as shown north of the Great Lakes in in Figure 26.6). In general, a weather map is created is by making observations. When plotted on a map, each observation is indicated by a symbol, such as the one in Figure 26.7, that describes the temperature, dew point, wind speed and direction, cloud cover and weather, if any.

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Figure 26.7 Weather Station Symbol: According to this weather station, the temperature is 60°F, the weather is moderate rain, the dew point is 55°F, the pressure is 1013.2 mb, the cloud cover is approximately 50%, and the wind is 15 knots from the southeast (Drawing by Robert Cohen)

weatHer forecasting There are two general ways of forecasting the weather. One way is to identify patterns and apply those patterns to the weather. For example, we have noticed that weather systems tend to move from west to east in the mid-latitudes. Consequently, if we are in the mid-latitudes and notice precipitation occurring to our west, we might forecast precipitation for our area. Similarly, a radar loop can show how the precipitation has moved during the past hour or so, and this can be used to predict what areas will experience precipitation in the next hour or so. While this first method is useful for short forecasts, it is not as useful for predicting how weather systems will evolve or where and when precipitation will likely form or decay. The second way of forecasting the weather is to use our knowledge of how the atmosphere works. For example, since we know that lowpressure systems tend to produce precipitation and storms, you can monitor the approach of storms simply by observing the air pressure at your location. If the air pressure is decreasing, that suggests that a low pressure system is approaching, possibly bringing precipitation and storms. On the other hand, if the air pressure is increasing, that suggests that higher pressure air is approaching, possibly bringing clearer skies. Furthermore, in the northern hemisphere, we know that a low pressure system will spin counter-clockwise. That means that east of the low pressure center, the winds will tend to be from the south (as shown in Figure 26.5) while west of the low pressure center the winds will tend to be from the north. Since air is warmer to the south (in the northern hemisphere), that means temperatures are typically warmer east of the low pressure center and cooler west of the low pressure center. In practice, you should use both methods to forecast the weather. The first method can provide a sense of where rain bands are moving, whereas the second method can be used to predict whether it will get warmer or colder. Meteorologists rely on the second method, in particular, to make forecasts for a day or more. To do so, they rely on computer models, which use equations of physics to specify the relationships between temperature, pressure and wind.

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The entire atmosphere is broken down into small blocks, with each block assigned a specific temperature based upon observations. The model then uses the temperature for each block to determine what the pressure is for each block and then uses the pressure differences between each block and the surrounding blocks to determine the wind for each block. The wind is then used to predict the change in temperature during a very short time (e.g., a minute). Of course, making a forecast for only a minute or so would not be too useful. So, the new temperature forecast is used to figure out the new pressure for each block which, in turn, is used to determine the wind for each block. The cycle is then repeated, over and over for each block, until the desired forecast time.

regional and local natUral factors tHat affect cliMate MoUntains and tHe rain sHadow

Much of what has been discussed so far assumes a uniform surface. In reality, we know that there are mountains and coasts and such and these things impact the weather. When the wind is blowing and there is a mountain in the way, the air is forced to either go over it or around it. For a mountain chain, the air goes up one side and down the other (as shown in Figure 26.8).

Figure 26.8 Mountains and Rain Shadow (Drawing by Robert Cohen)

As the air ascends, it expands and pushes the other air out of the way. This expansion cools the air (even if the air it pushes out of the way happens to be warmer). If the air cools below the dew point, condensation occurs and a cloud forms. For this reason, clouds and precipitation can occur on the side of the mountain where the air is ascending, whereas it is drier on the opposite side (since the water had condensed and fallen out of the air). As the air descends down the other side of the mountain, it warms back up because the air gets compressed as it descends. The descending air is actually warmer than the ascending air since energy is added to the air when water condenses.

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land/sea Breeze

Breezes can be set up along the coast because of differences in air pressure between the land and the sea. During the day, the land gets warm, which results in a lower pressure. Wind blows from the sea, now at a higher pressure, toward the land. This is called a sea breeze. At night, we observe the reverse circulation, called a land breeze. The land gets cold, which results in a higher pressure. Wind then blows from the land, now at a higher pressure, toward the sea.

How HUMans affect and are affected By cliMate HUMan inflUences on cliMate

The sun is the major driver behind climate. However, human activities are also known to affect climate. For example, how much the surface warms during the day depends on how dark the ground is (darker hues will absorb more solar radiation and thus warm more) and whether the ground is moist (some of the solar energy is used during evaporation). Human activity can drastically change these characteristics, however. For example, urban areas tend to be warmer than the surrounding areas because of the effect of activities such as cutting trees (removing moisture) and covering the ground with asphalt (making the ground darker). This is called the heat island effect. The heat island effect only warms the urban area. It does not lead to other areas getting warmer. On the other hand, the burning of fossil fuels produces carbon dioxide, which is a greenhouse gas that impacts the overall temperature of the Earth.

cliMatic inflUences on HUMans

Climate has a huge effect on humans. We plan our days around the weather and we plan our communities around the climate. Normal weather changes are typically not a problem. We know how to deal with those. Unexpected changes can be devastating, however. Floods, blizzards, heat waves and droughts are just a few examples where extreme weather can be problematic both in terms of human health as well as in property losses. Longer-term changes are also problematic. A major volcanic eruption, for example, can put a lot of dust in the upper atmosphere, leading to cooler than normal temperatures for an extended period of time. The 1816 “year without a summer” in parts of the United States and Europe may have been caused, in part, by the eruption of Mount Tambora (Indonesia) in 1815.

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review QUestions—cHaPter 26 1. Which of the following is most responsible for the temperature warming with height in the stratosphere? a. The absorption of solar radiation at the Earth’s surface. b. The absorption of solar radiation by ozone in the upper atmosphere. c. The absorption of solar radiation at the top of the atmosphere. d. The mixing of air in the troposphere. e. The mixing of air in the stratosphere. 2. Oxygen makes up what fraction of the atmosphere? a. 100% b. 80% c. 20% d. 1% e. There is no oxygen in the atmosphere. 3. The equator is warmer than the poles principally due to which of the following reasons? a. The equator is closer to the Sun than the poles. b. There are more hours of daylight on the equator than on the poles. c. At the equator the Earth’s surface is perpendicular to the sun’s rays. d. There are more trees on the equator than near the poles. 4. In the mid-latitudes (30° to 60°), in which direction do winds in the troposphere tend to blow? a. Toward the north. b. Toward the south. c. Toward the east. d. Toward the west. 5. Which of the following circulations would most likely have the longest life cycle? a. Microscale circulations such as eddies produced by trees and buildings. b. Mesoscale circulations such as thunderstorms and tornadoes. c. Global circulations such as the prevailing westerlies of the mid-latitudes. d. All sizes of circulations have similar lengths of their life cycle. 6. A wet towel is hung out to dry. In which case would it dry quickest? a. 80°F and 100% relative humidity. b. 40°F and 100% relative humidity. c. 40°F and 50% relative humidity. d. The towel wouldn’t dry in any of these cases. e. The towel will dry in the same amount of time for all the cases.

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7. Suppose the entire troposphere is below 0°C (32°F), the freezing point of water. Which of the following precipitation types is most likely? a. Rain. b. Freezing rain. c. Sleet. d. Hail. e. Snow. 8. Which of the following air masses would most likely cause hot and muggy conditions along the east coast of the United States during the summer? a. continental polar. b. maritime polar. c. continental tropical. d. maritime tropical. 9. Suppose the tomorrow’s weather is predicted to be rain. Which of the following observations would be consistent with the rain being associated with a low pressure system? a. Falling pressure and winds from the south. b. Falling pressure and winds from the north. c. Rising pressure and winds from the south. d. Rising pressure and winds from the north. 10. Which of the following is indicative of a cold front passing through? a. Rain and then falling temperatures. b. Rain and then rising temperatures. c. Clear skies and falling temperatures. d. Clear skies and rising temperatures. 11. In Figure 26.6, what kind of feature is indicated by the line that crosses the Great Lakes? a. Cold front. b. Warm front. c. Stationary front. d. Occluded front. e. Dry line. 12. Which of the following forecasts is most appropriate for point A on the map shown in Figure 26.6? a. Rain today then clearing with cooling temperatures. b. Rain today then clearing with warming temperatures. c. Clear today then rain with cooling temperatures. d. Clear today then rain with warming temperatures.

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13. Air of temperature 20°C and dew point 15°C starts up one side of a mountain. What is the likely temperature and dew point on the other side of the mountain? a. 20°C temperature and 15°C dew point. b. 15°C temperature and 15°C dew point. c. 15°C temperature and 10°C dew point. d. 25°C temperature and 15°C dew point. e. 25°C temperature and 10°C dew point. (Answer Key: 1.b, 2.c, 3.c, 4.c, 5.c, 6.c, 7.e, 8.d, 9.a, 10.a, 11.a, 12.a, 13.e)

Chapter 27

ASTRONOMY David Buckley

Units of distance The universe is big, too big for our tiny minds to imagine. For this reason astronomers use units of measurement that are unlike any others. For example, the distance between the Sun and the planet Mercury is about 36 million miles. So if someone was to ask you “Is Mercury far from the Sun?” What would you say? Thirty-six million miles is certainly a huge distance. However, unless you knew that Mercury is the first planet from the Sun, or that the Earth is 93 million miles from the Sun, you would have a hard time judging. So astronomers have invented a special “yardstick” to measure distances in the solar system—the Astronomical Unit or AU. One AU is equal to the Earth’s average distance from the Sun, or about 93 million miles (150 million kilometers). The convenience of the AU as a measuring stick is that we can express the distance of other planets as multiples or fractions of the Earth’s distance from the Sun. For instance, Mercury is 0.39 AU from the Sun. Because this is a decimal number less than 1, you know immediately that Mercury is closer to the Sun than we are. Mars resides about 1.5 AU, or 50% farther from the Sun than us. Jupiter is about 5 times farther from the Sun (5.2 AU) and Saturn is just under 10 times farther than we are (9.5 AU). The farthest major planet from the Sun is Neptune. It’s about 40 times farther from the Sun than Earth is (40 AU). It took the Voyager spacecraft 12 years to journey from Earth to Neptune in the 1970’s and ‘80’s. Yet, when it reached Neptune, Voyager was only one ten-thousandth of the distance to the nearest star to our Sun! The stars are at enormous distances from us. Even the closest are hundreds of thousands of AU’s from our solar system. So the AU is much too small

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of a yardstick to measure distances to stars. Instead, we turn to the fastest thing in the universe, light, to help us measure these vast distances. Light is so fast that it could circle the Earth seven times in a second. Yet it takes sunlight eight minutes to get to us from the Sun’s surface. So we could say that the Sun is eight “lightminutes” from the Earth. The outermost planets are a few “light-hours” from us, but it takes light years to journey the vast distances between the stars. For this reason, astronomers often measure the distances to stars in light years. A light year is about 9.5 trillion kilometers. The light year also has another wonderful aspect as a unit of measurement. It tells us how far back in time that we are seeing. For example, the star Vega is about 26 light years away from us, so when we see Vega on a clear summer night, we are seeing light that left its surface 26 years ago. When we look at the many stars in the night sky, we are seeing them all at different times in the past, depending upon their distances. Professional astronomers more often use a unit called the parsec (pc) to measure interstellar distances. A parsec is 3.26 light years, and is slightly less than the typical spacing of stars in our region of the Milky Way galaxy. Galaxies are immense conglomerations of hundreds of billions of stars that are often hundreds of thousands of light years across, separated by distances of millions of light years. Therefore, astronomers use kiloparsecs (kpc), which are units of a thousand parsecs (just like a kilometer is a unit of a thousand meters) to measure distances within our galaxy. For distances to other galaxies, astronomers use an even bigger measuring stick of megaparsecs (mpc), or millions of parsecs.

origin and life cycle of stars. If it wasn’t for gravity, stars could not exist, and it would be a cold and dark universe. Gravity is the force that pulls all masses together, but you need a lot of mass all in one place for gravity to really do its job. Fortunately, there is a great deal of gas and dust in our galaxy in Giant Molecular Clouds. Sometimes, parts of these clouds get “clumpy” or dense enough so that gravity starts pulling everything toward the center of the clump. As the clump shrinks in on itself, it gets hotter and hotter, as gravitational energy is turned into heat. It eventually becomes a young star when the central temperature is hot enough for the star to create its own nuclear energy. The nuclear fusion in the core is what makes the star shine and it helps the star provide enough gas pressure to keep it from collapsing under the force of its own gravity. Stars spend the longest part of their lives (the “prime of their lives”) as main sequence stars, turning hydrogen into helium in their cores. The biggest, most massive of these stars are the brightest, sometimes up to 100,000 times as bright as our Sun, and are the “gas guzzlers” of the universe. They shine hot, blue and bright. They live fast and die young! The puny, red, low mass stars are the “misers” of the universe. They burn so faintly, sometimes only 1/10,000th as bright

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as our Sun, and slowly, that their life spans are much longer than larger stars. Stars don’t last forever. They can only battle gravity for as long as their fuel supply lasts. When the fuel runs out, the star cools off and gravity starts to make it shrink again. Most stars try to burn their “garbage,” which is composed of the helium they produced during the prime of their lives. When they succeed, they become very bright and their outer layers inflate to produce a Giant or Supergiant star. But even the garbage runs out, and when that happens, the star’s core begins to collapse. A star’s final collapse generally results in one of three exotic objects, a white dwarf, a neutron star, or a black hole. Medium and low mass stars like our Sun will lose their outer layers and their central cores will collapse to a sphere the size of Earth (about a million times more dense than solid rock). This hot but faint ember is called a white dwarf. It is the remains of a star that will slowly cool off for billions of years. Big, heavy stars go out with a bang. The collapse of their cores, which has made elements as heavy as iron during their supergiant stage, will be quick and violent, so violent that the outer layers of the star will be blown out into space in a spectacular supernova explosion. The collapsed core that remains after the supernova will be either a neutron star or a black hole. Neutron stars are so dense that a sugar cube sized piece of one would weigh as much as a mountain. Imagine a million mile wide star crushed to the size of a city and spinning like a high speed lighthouse beacon several times a second. Pulsars are such spinning neutron stars and are sometimes found in the center of the ragged remains of supernova explosions. Sometimes, the core of a star is too heavy to be kept from collapsing even by the incredibly dense material of a neutron star. If so, it will crash through the neutron star stage and shrink to a tiny point. The surrounding region of space will be cut off from the rest of the universe. The strength of its gravity will be so great that not even light can escape. This is a black hole. If a black hole is far away, its gravity is not any stronger than a normal heavy star. But since gravity gets stronger the closer you get, and you can get really close to the mass at the center of a black hole, the gravity gets incredibly intense and has profound effects on the nature of space and time.

cHaracteristics of tHe sUn Many textbooks say that the Sun is an average star. This is only true if you consider scoring in the 95th percentile of a test as “average.” Ninety five percent of the stars in our galaxy and the universe are smaller and dimmer than our Sun. However, the really heavy, bright stars of our galaxy are so much brighter and more spectacular that they make our Sun seem rather ordinary. But it’s not a bad thing, because if our Sun was more spectacular it would live a very short life and it would also be too hot for life on Earth to exist. For us, the Sun is just right.

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The Sun looks like it has a definite surface. But it is not solid. It is a hot ionized gas all the way through. The visible surface of the Sun, called the photospherere, is where the Sun becomes opaque. Just like a puffy, white fair-weather cloud seems to have a definite “edge,” the Sun also seems to have an edge. The cloud, inside that “edge,” is like a hazy fog. Inside the photosphere, the Sun is like a very hot bright fog. We can’t see through the Sun, just like we can’t see through the cloud, because light is scattered all over and can’t travel in a straight line. Because the Sun is a hot ionized gas, its interior is really more like the inside of a flame or a shimmering fluorescent light bulb, because the light is scattered by electrons rather than the tiny water droplets that are found in a cloud. Just inside the Sun’s photosphere the hot gasses are churning turbulently like a hot pot of soup. This is a process called convection, where hot blobs of gas called granules are rising, releasing their heat at the photosphere, then sinking back down to get warmed up again, like the blobs of wax in a lava lamp. Occasionally, a magnetic disturbance at the photosphere will trap a bunch of these blobs so that they cool off more than normal. The cooler trapped patch of gas gives off less light than the surrounding hotter gas and so appears to us as a darker sunspot on the face of the Sun. Individual sunspots are like blemishes, because they come and go. But there is a sunspot cycle, where the sun goes from lots of blemishes, to very few, and then back again about every 11 years. The churning convective region only extends about one-fourth of the way from the photosphere to the Sun’s center. Inside are the radiative region and the central core. The core is where the action is! That’s where temperatures between 10 and 15 million degrees Kelvin force hydrogen nuclei (protons) to smash together to become helium nuclei, creating several particles (photons) of energy in a process known as nuclear fusion. The newly created photons don’t know which way is out, and there are electrons about every centimeter or so that try to push them in a different direction. So the Sun’s radiative zone is like a giant 3-D pinball machine with the photons getting bumped all over the place as they try to get out. Surrounding the Sun’s visible photosphere is the dimmer atmosphere or “chromosphere” and the even dimmer but vast “corona” that extends over a million miles into space. They are both only visible on the Earth’s surface during a total eclipse, when the Moon hides the brilliance of the photosphere.

tHe solar systeM The solar system consists of our Sun, eight major planet, dozens of moons, a few dwarf planets, and countless comets, asteroids and meteoroids. Of the eight major planets, the four inner or Terrestrial planets (Mercury, Venus, Earth & Mars) are relatively small, dense and have solid surfaces. The four outer or Jovian planets (Jupiter, Saturn, Uranus & Neptune) are large, low in density, and have no solid surface upon which to land.

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Generally speaking, bigger planets hold on to their internal heat longer than small planets, just like a cake taken out of an oven will take longer to cool than a cupcake. So the smallest bodies of the inner solar system, our Moon and Mercury, cooled off quickly. Because they are cold inside, there is no heat to drive geological processes like volcanoes and crust motion that might erase craters that formed when the planets were young. Also, because they are small, their weak gravity makes it impossible for them to hold on to a gaseous atmosphere, so that there is also no wind or weather erosion to change the surface. Because of this, the smallest bodies tend to have surfaces that are changed the least by weathering and geological processes. The largest of the inner planets, Earth and Venus, both have atmospheres which, especially for Earth, can cause erosion and change the surface. Both are also large enough to have held on to more of their internal heat. This heat drives geological processes like volcanoes, earthquakes and mountain building on Earth and, to a lesser extent, on Venus. This is why you will find very few craters on the surface of Earth and Venus. Their surfaces have been modified through a combination of erosion by their atmosphere and changes due to internal geological forces. Mars is a “tweener,” larger than the Moon and Mercury but smaller than Earth or Venus. Mars held on to its internal heat long enough to form huge volcanoes, lava fields and canyons on much of its surface. However, its interior has since cooled off and it is now geologically dormant, and still retains a heavily cratered moonlike surface over more than half of its surface. There is some wind erosion due to its thin carbon-dioxide atmosphere. The outer Jovian planets do not have solid surfaces. Once called the “Gas Giants” because they are made mostly of light gasses, these gasses are liquefied due to the high pressure inside these large planets. Jupiter and Saturn both have a candy striped pattern of clouds on their visible surfaces, outlining rapid jet streams in their atmospheres that may be driven as much by their internal heat as by heat they receive from the Sun. They both have fierce winds and long-lived hurricane-like storms in their atmospheres. Each of the Jovian planets has a mini-solar–system of moons. Some of these moons, like Jupiter’s moons Ganymede and Callisto and Saturn’s moon Titan are similar in size to the planet Mercury and would be considered planets if they were orbiting around the Sun. Most are rather icy bodies. Saturn, Uranus and Neptune also have rings of icy particles, while Jupiter’s small ring seems to be made of tiny dust particles. In addition to the major planets, there are thousands of rocky asteroids in the Solar System. They mostly orbit the Sun in the asteroid belt, between Mars and Jupiter. The first object discovered in the asteroid belt, Ceres, in 1801, was first labeled a new planet, but then downgraded to a “minor planet” a few years later when more objects were found there. It is now considered a “dwarf planet” and is the largest object in the asteroid belt.

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Pluto is also now considered a dwarf planet. The problem is that Pluto was discovered about 60 years too soon, long enough for many people to get emotionally attached. It was designated as the ninth planet when it was discovered by American astronomer Clyde Tombaugh in 1930. However, in the early 1990’s, advances in technology allowed dozens of other Pluto-like bodies to be found out beyond Neptune. These icy bodies in what is now called the “Kuiper belt” are similar to, but larger than, most comets. Since some of these objects are even larger than Pluto, it was inevitable that Pluto would be downgraded from a major planet, just as Ceres was. Comets spend most of their existence in the outer Solar System. We only notice them when they fall into the inner solar system. The Sun’s heat then vaporizes their surface, releasing dust and gas that is blown back by the sunlight creating an often spectacular head and tail.

eartH’s Motion and Units of tiMe It was confirmed a mere four centuries ago that the Earth spins on its axis once a day and orbits around the Sun once a year. Indeed, that’s where we get the units of time for days and years. Without the Earth’s motion, both units of time would be meaningless. The Earth actually spins on its axis a full 360 degrees relative to the distant stars in about 23 hours and 56 minutes (the Earth’s Sidereal rotation). But since the Sun is so much more important to us in telling time, we set our clocks according to how the Earth spins relative to the Sun. Because the Earth travels about one degree in its orbit around the Sun each day, the Earth has to spin about 361 degrees to make the Sun appear in the same place in the sky. This takes about 4 minutes longer than the actual Sidereal rotation. So a Solar Day on Earth (the time between noon and noon the next day or sunrise and the next sunrise) is 24 hours long. Since we tell time by the Sun, one very important time of day is mid-day or noon, when the Sun is halfway between sunrise and sunset. The Sun, of course, seems to move East to West across the sky because the Earth is turning toward the East. The meridian is an imaginary arch separating the eastern half of the sky from the western half. So the Sun spends the morning hours in the eastern sky (ante-meridian or a.m.), crosses the meridian at noon (its highest point in our sky) then spends the afternoon (post-meridian or p.m.) in the western sky. Since the Earth is round, noon for someone in New York is going to be different than noon for someone in Los Angeles. So the Earth is divided up into 24 time zones that are about 15 degrees of longitude wide. People in a specific time zone set their clocks according to when noon occurs for them. Someone in a time zone just to the east of you will have noon occur an hour earlier, and so their clocks will be set one hour ahead of yours. Someone one time zone to the west will be an hour behind you because their noon will occur one hour later. If you live in the center

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of a time zone, noon usually occurs about the time it’s supposed to, when the Sun is crossing the meridian. But if you live on the eastern or western margins of a time zone, astronomical noon might occur up to a half hour early or a half hour late respectively. And of course this is only for standard time. When we “spring ahead” to daylight savings time in March every year, we shift astronomical noon to 1 p.m., effectively borrowing an hour of daylight from the early morning and putting it in the evening where it is more useful for people coming home from work.

eartH’s seasons One of the biggest misconceptions in all of astronomy is that seasons are caused by our distance from the Sun. It is true that the Earth’s distance from the Sun varies slightly (about +/- 2%) during the year, so it seems only natural that people would conclude that we would have summer when we are closer to our celestial “campfire” and winter when we are farther away. Two facts immediately show this to be false. First, we are closest to the Sun around the 2nd week of January (the dead of winter for us in the northern hemisphere) and farthest from the Sun around the Fourth of July (when we are having summer cookouts and pool parties)! Second, the seasons are reversed in the southern hemisphere. Since we are all on the same planet, how could someone in Australia be closer to the Sun at the same time we are farther from the Sun? They can’t, and so distance from the Sun has nothing to do with the seasons. One obvious change that does seem to go hand in hand with the change in seasons is the length of the days and nights. In summer, the days are longer and the nights are shorter. In winter, the reverse is true. Since we warm up when the Sun is up during the day and cool off when it is down at night, it is clear that one of the reasons we have seasons is the amount of time the sunlight strikes various parts of the earth at different times of the year. The second, less obvious, change that is related to the seasons is the height of the Sun in the daytime sky. Though surprisingly few people seem to notice, the Sun is much higher in the summer sky and much lower in the winter sky. Because the Sun is so low in the sky in the winter, its heating rays are spread out over a much larger area of the Earth’s surface, making for very inefficient heating. In the summer, the Sun’s rays shine down at a more direct angle and so they heat the surface much more efficiently. So it’s a “double whammy.” In the winter, we not only get less hours of sunlight, but the sunlight that we get is at a less direct angle. In summer, we get long hours of very direct sunlight which, on a sweltering summer day, might seem like too much of a good thing. What is the underlying cause of all this? The answer to this question is the tilt of the Earth’s axis. As the Earth orbits around the Sun, as though on a flat table-top, its spin axis (its north and south poles) does not point straight up and

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down, but at a 23 ½ degree angle. Over the short term, the Earth doesn’t wobble as it goes around the Sun, but maintains its orientation in space (our North Pole pointing toward Polaris, the “North Star”). Therefore, on one side of the Sun (as shown in Figure 27.1) the northern hemisphere seems to be bowing toward the Sun, causing the long days and more direct solar rays of summer. Six months later, we are on the other side of the Sun (as shown in Figure 27.1), and the northern hemisphere seems to be tilted away from the Sun, causing long cold nights and the low Sun angle of winter days! But remember, it’s NOT about distance. When we are tilted away in winter, people in South America are tilted toward the Sun and have the long warm days of summer!

Figure 27.1 Seasons and the tilt of the Earth’s axis. (Drawing by David Buckley)

eartH-Moon-sUn systeM As the Earth goes around the Sun once a year, our Moon faithfully follows along in orbit around us. It takes about 4 weeks (27.3 days to be more precise) for the Moon to orbit the Earth relative to the stars (its sidereal period). That means that if the Moon is in a particular constellation tonight, it will be back in that same constellation in the sky in 27.3 days (as shown in Figure 27.2). This is where we get the idea of a month, which comes from the root word “moon.” But since you can’t fit a nice even number of lunar months in a year, we tack on a few days on most months to make 12 of them fit into a year. The cycle of phases (or synodic period) depends on the alignment of the Moon with the Earth and the Sun. At the same time that the Moon is orbiting the Earth, the Earth is travelling about 1 degree per day in its orbit around the Sun. Therefore, at the end of one orbit, the Earth has travelled about 27 degrees or so around the Sun. So to re-align itself with the Sun, the Moon has to go an extra 27 degrees or so in its orbit, which takes it about two more days for a total of 29 ½ days.

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In Figure 27.2, the first image shows the Earth, Moon and Sun lined up. The second image shows the Earth and Moon after the Moon has completed one orbit (its sidereal period). But because the Earth and Moon have travelled around the Sun, it takes a little over two days for them to line up again.

Figure 27.2 The relation between the Moon’s sidereal and synodic periods. (Drawing by David Buckley)

PHases of tHe Moon What does cause the Moon’s changing appearance or phases? Just like the Earth, the Moon is a solid round object, and just like the Earth, sunlight can only fall on half of the Moon at any moment. So like Earth, the Moon has a daytime side and a nighttime side. Since the Moon travels around the Earth, we see different amounts of the daytime side and the nighttime side, depending on its angle from the Sun in our sky. When it’s less than 90 degrees from the Sun in the sky, (as shown in Figure 27.3) it is slightly closer to the Sun than we are. So we see more of its nighttime side, and the Moon will appear as a Crescent (or as the unviewable New Moon when the entire night side is pointed at us). When it’s more than 90 degrees away from us, it’s slightly farther from the Sun than we are. Then we see more of the daytime side of the Moon and it appears more than half illuminated. At those times, it will be either a Gibbous Moon, when we see most of the illuminated side, or a Full Moon, when the entire day side is pointed toward us and the Moon is exactly opposite the Sun in our sky. Twice a month, we will see the Moon almost exactly 90 degrees from the Sun in our sky, and we will see it look like a “half” Moon. When it is one fourth of its way around its cycle, going from “waxing” crescent, to “waxing” gibbous we call that First Quarter. When it’s ¾ of the way around, transitioning from “waning” gibbous to “waning” crescent, we will see its other half and call it Third Quarter (or sometimes Last Quarter).

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Figure 27.3 Moon Phases (Drawing by David Buckley)

ecliPses Based on Figure 27.3, it would seem that every time there is a New Moon we would expect the Moon to block out the Sun as seen from Earth and cause a Solar Eclipse. We might further expect that every time there is a Full Moon, the Moon should pass into the Earth’s shadow causing a Lunar Eclipse. But that just doesn’t happen very often! There are two problems with Figure 27.3. First, the Earth and Moon are drawn much bigger than they really are compared to the Moon’s distance so that you can see them and still fit the diagram on the page. Therefore, the shadows cast and the possible targets they will be cast are much smaller than they appear. Second, the page is a two dimensional flat surface, and space is 3-D! If you imagine that the flat page represents the flat plane of the Earth’s orbit around the Sun, the Moon’s orbit would not be on that flat page, but would be tilted by five degrees. Each month the Moon would spend half of its orbit “above” the page and the other half of its orbit “below” the page. In other words, at New Moon, the Moon usually passes either above or below the Sun as seen from the Earth, and at Full Moon, the Moon usually passes either above or below the Earth’s shadow. During most months, the Moon is “too high” or “too low” for an eclipse to happen. However, there are two places where the Moon crosses the plane of the Earth’s orbit (our imaginary flat “page”). These two crossing points are called nodes and twice a year, the nodes become lined up perfectly with the Earth and

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Sun. But that doesn’t guarantee an eclipse because the Moon has to show up in the right place at the right time. If the Moon is New when the nodes are lined up, it will pass precisely between the Earth and Sun, and there will be a solar eclipse. If the Moon is full when the nodes are lined up, it will pass directly behind the Earth and into its shadow, causing a lunar eclipse. The darkest part of the Moon’s shadow, called the umbra, points directly away from the Sun and is the shape of a long skinny cone. The part of the Moon’s umbra that reaches Earth during a solar eclipse is so narrow that it makes a spot less than 200 miles wide. This dark spot sweeps across the Earth’s surface very fast and if you are standing along the path of the shadow the entire visible disk of the Sun will be obscured for several minutes. This is a total solar eclipse, the most spectacular kind. The sky will go dark in the middle of the day, the ghostly glow of the corona will appear around the silhouette of the Moon’s disk, and several bright stars and planets will be visible. Luckily, these eclipse paths can be precisely predicted years in advance in case you want to travel to see one. But if you are not directly in the path of the Moon’s umbra, you may still be in the path of its larger penumbra, where there is a partial solar eclipse. It is the partial part of the solar eclipse that is dangerous to stare at, mainly because the Sun is always too bright to stare at without damaging your eyes. However, there are several perfectly safe methods for viewing a partial solar eclipse such as safe solar filters, eclipse glasses, and several simple projection techniques. A special type of partial eclipse is an annular solar eclipse. Often dramatically called a “ring of fire” eclipse, an annular eclipse happens because sometimes the Moon eclipses the Sun when it is in one of the farther points of its orbit around the Earth and the cone of the umbra comes to a point before it reaches the Earth. So if you are standing right in the path below the umbra, you will see a Moon that looks too small to cover the Sun, and a ring or annulus of the Sun’s visible surface will surround the silhouette of the Moon. Lunar eclipses are usually seen by many more people than total solar eclipses, because instead of needing to be in the narrow path of the Moon’s umbra, you merely have to be on the side of the Earth that is facing the Moon while it goes into the Earth’s shadow. So a lunar eclipse will be visible from at least half of the Earth’s surface. One of the curious things about a total lunar eclipse is that even when the Moon is completely immersed in the darkest part of the Earth’s umbra, it still can be seen glowing a coppery red color in the sky! This would not be possible if not for the Earth’s atmosphere. It’s the air around us that scatters sunlight. That’s why we have twilight even after the Sun goes down in the evening. It’s the Earth’s atmosphere that scatters enough sunlight toward the eclipsed Moon to give it the coppery red glow. If you were an astronaut on the Moon during a lunar eclipse, you would see the Earth in the lunar sky eclipsing the Sun. But there would be a bright reddish ring around the silhouette of the Earth. You would be looking at all the sunrises and sunsets all over the world at the same time.

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satellites and geosyncHronoUs orBits. The Moon is our only natural satellite. A satellite, by definition, is an object that is in orbit around a planet, but what is an orbit and why don’t satellites fall down? Well, actually they are falling, but they keep missing the ground. This is going to require some explanation. Imagine that you throw a ball perfectly horizontally. The ball will start falling in a curved path to the ground as soon as you release it. The faster you throw it, the more gradual the curve, and the farther it will go before it hits the ground! Now imagine you are up on a high tower with a high powered rifle or cannon. So high, in fact, that you have to wear a space suit because you are above the Earth’s atmosphere. If you fire the cannon, the shell will travel a great distance before it hits the Earth’s surface. But the Earth’s surface is curved, not flat. So if you increase the speed of the cannon’s shell, it might travel ¼ or even one-half of the way around the Earth before hitting the ground. Eventually, if it’s fired fast enough (about 17,500 mi/hr), it will curve toward the Earth so gradually that it will fall completely around the Earth and hit you in the back of the head 90 minutes later. That is orbiting. The shell continuously falls to Earth but never reaches the surface because the Earth passively “gets out of the way” due to its spherical shape! And since it is falling, any passengers inside the projectile will be in free-fall and will feel weightless, even though there is plenty of gravity pulling them toward the Earth’s surface. At a much greater height, say at 22,272 miles, the Earth’s gravity is significantly weaker, so anything you launch sideways will fall to Earth more slowly than it did only 100 miles up. This means that a satellite at that height can travel at a slower speed to fall around the Earth in a perfectly circular orbit. Since it travels more slowly and has a larger orbit, it takes 24 hours to orbit instead of 90 minutes for the much lower orbit. But this is the same time it takes the Earth to rotate, so if you are a careful rocket scientist, and put your satellite into this special type of orbit above the equator, it will seem to hover over one spot on the Earth’s equator forever. This is the only altitude at which satellites can seem to stay in the same place relative to the Earth’s surface. It’s called a geosynchronous orbit because it is synchronized with the Earth’s rotation. Geosynchronous satellites were first proposed by science fiction writer Arthur C. Clarke in 1945 and they are now used for communications satellites and the weather satellites that give us continuous images of weather patterns and developing storms. This is the reason that satellite TV dishes can point to a single place in the sky and continue to get signals without ever having to move.

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contriBUtions of Manned and UnManned sPace Missions Spaceflight began in October 1957 with the orbiting of “Sputnik I” by the Soviet Union and accelerated rapidly thereafter, due in large part to cold war rivalries. While the use of unmanned satellites for communications purposes or weather prediction blossomed because of commercial or scientific interests, human or “manned” spaceflight was almost entirely prompted by the rivalry between the United States and the Soviet Union. Americans were shocked when the Soviets became the first to put a human into orbit in 1961. A short time later, after Alan Shepherd became the first American in space on the first brief sub-orbital flight of Project Mercury, President John F. Kennedy set a goal to land a man on the Moon and return him safely to Earth by the end of the decade (a mere 8½ years away). The space race continued throughout the 1960s with the Soviets chalking up the first multi-passenger flights, the first woman in space, and the first “space walk.” Through the remainder of the Mercury program and then into Project Gemini, the Americans caught up and surpassed the Soviets by concentrating on skills necessary for a Moon mission, including long duration flight, rendezvous (two space craft meeting in orbit and flying in formation), and docking (the joining up of two spacecraft in space). Though the Apollo Moon program began tragically with the fatal fire that killed 3 astronauts in a pre-flight launch pad test, the delay of a year and a half refocused the NASA team on safety and details. After four Apollo test flights, including the memorable 1968 flight of Apollo 8 to orbit the Moon, the first landing on the Moon was completed on July 20, 1969 by Neil Armstrong and Edwin Aldrin. In the following 3½ years, 5 more landings were made and a total of 12 men walked on another world. Although the initial aim of the Apollo program was political, not scientific, the Moon missions provided a treasure trove of scientific information on the history of our Moon and the solar system. In recent years, conspiracy “theorists” have come up with shallow arguments that they say suggest that the Moon landings were faked, and staged here on Earth. Their claims can be easily dismissed with two pieces of evidence. First, the Moon rocks brought back to Earth by the Apollo astronauts are unlike anything that can be found or manufactured on Earth and have been circulated among geologists for in-depth study for the last 40 years. Secondly, the space race was a competition, one that the Soviet Union was not happy to lose. The Soviets had large radio telescopes and could have easily proven that we had faked the Moon landing if the astronauts’ radio signals were not coming from the Moon. Some of the greatest explorations of our Solar System have been done by robotic spacecraft. An armada of spacecraft has been sent to Mars over the years, with seven of them successfully landing. The rovers Spirit and Opportunity, designed to last for only three months, explored the surface of Mars for over six years. The various orbiters and landers have painted a picture of Mars that shows

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that it was a much more dynamic planet in the distant past, with more Earth-like temperatures and liquid water on part of its surface. Evidence of life, the “Holy Grail” of Mars exploration, has remained elusive. The greatest surveillance of the outer solar system was completed between 1977 and 1989, when the Voyager spacecraft visited the giant Jovian planets. In addition to the impressive, alien weather patterns and colossal storms on these planets, the Voyagers showed us dozens of interesting moons, including one with active volcanoes (Io), one with a possible subsurface ocean (Europa), and one with a thick atmosphere and possible seas of liquid methane (Titan). But the spacecraft that has likely expanded our knowledge of the universe more than any other is the Hubble Space Telescope which is in low Earth orbit, only 200 miles or so above the Earth’s surface. The Hubble is a respectable size, though its 92” diameter mirror is dwarfed by many observatory telescopes on the surface of Earth. The advantage of the Hubble is that it is up above the Earth’s distorting atmosphere, so it can observe distant stars and galaxies with a resolution and sensitivity greater than telescopes here on Earth.

scientific contriBUtions of reMote sensing Astronomy is different than other sciences because astronomers cannot do controlled experiments or analyze samples in the laboratory (other than the aforementioned Moon rocks or occasional meteorites that fall to Earth). Because of this and the extreme distances involved, astronomers rely heavily on remote sensing. Remote sensing involves using electromagnetic radiation, which includes various types of “invisible light” like radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays to study the universe. By using our understanding the nature of light and how celestial objects either give off or interact with light, both visible and “invisible,” we can glean information about the nature of these objects. This allows us to discern the physical properties of stars and galaxies that are thousands or even many millions of light years away. With the advent of satellites, it became possible to use remote sensing to look back on and study the Earth. One might wonder why it’s useful to leave the Earth to study it. Well, the simple answer is to improve the view. From orbit, you can get an overall view of large parts of the planet at once. From orbit it’s just as easy to view remote or inaccessible areas as heavily populated ones. The most obvious type of remote sensing that we experience in our everyday lives is the images from meteorological satellites of weather patterns that we see every evening on the local weather forecast. Visible images from these geosynchronous satellites stationed high above the equator can show us cloud patterns and tropical storms forming. Infrared photos can show us clouds even at night and give us information about their temperature. Lower orbiting satellites scan the surface using infrared radiometers that can give us global maps of both land and sea surface temperatures. A well known ap-

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plication of this is the monitoring of phenomena such as El Nino, the warming of water in the eastern pacific that can have far reaching effects on the weather in North America. Other satellites scan the Earth with various sensors to collect information about deforestation, agriculture, erosion, and mineral resources. Thus, remote sensing gives us the ability to get a truly global view of our planet.

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review QUestions—cHaPter 27 1. The light year is a unit that most often describes a. the length of time that the Earth travels around the Sun. b. the distance between planets of the solar system. c. the distance between stars in our galaxy. d. the age of the Universe. 2. The thing that determines the life cycle of a star more than anything else is a. its color. b. how massive it is. c. its location in the galaxy. d. how fast it spins. 3. The hottest part of the Sun is a. the sunspots. b. the convective region. c. the core. d. the chromosphere. 4. The inner planets are small and dense while the outer planets are big and have low densities. This is primarily because a. heavy materials are more attracted to the Sun than lighter materials. b. low density materials were driven away from the inner solar system by the solar wind. c. dense objects spin around the Sun faster and so they must be closer. d. only dense materials can survive the heat of the inner solar system and form planets. 5. The Earth is a geologically dynamic planet with earthquakes, volcanoes and moving continents. Mercury, on the other hand, is a geologically dead world still bearing the craters that it has had for billions of years. Why is this? a. Mercury is a small world that lost its internal heat rapidly while Earth is big and has never cooed off completely. b. The Earth has an atmosphere and Mercury does not. Geological processes need an atmosphere. c. Mercury spins too slowly for Geological processes to get started. d. Mercury’s heat is all on the outside, because it is so close to the Sun.

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6. It is much hotter in the summer here in the northern hemisphere because a. we are closest to the Sun in the summer time so we get more intense rays. b. the Earth’s tilt causes more hours of daylight and higher Sun angles in the summer. c. the Earth’s tilt causes the spin of the Earth to be slower in the summer. d. greenhouse gases build up more in the summer due to the Earth tilting toward the Sun. 7. Which is true of the Earth-Moon-Sun system? a. The Earth revolves around the Moon as the Moon revolves around the Sun. b. The Moon revolves around the Earth as the Sun revolves around the Earth. c. The Sun revolves around the Moon as the Earth revolves around the Sun. d. The Moon revolves around the Earth as the Earth revolves around the Sun. 8. The phases of the Moon that we observe from Earth are caused by a. the Earth’s shadow falling on the Moon and obscuring different amounts. b. the motion of the Moon around the Earth lets us see different amounts of its daylight side and night side. c. clouds obscure different areas of the Moon’s surface each month. d. craters on the Moon make parts of it look darker than other parts, and the Moon’s rotation lets us see more of the cratered areas sometimes and less at other times. 9. Why have more people seen total eclipses of the Moon rather than total eclipses of the Sun? a. Because the Moon is in the sky more often than the Sun. b. Because the size of the Moon’s shadow (umbra) is very small during a total solar eclipse, and you have to be standing right in it to see the total eclipse. c. Because total lunar eclipses last so much longer than total solar eclipses, it gives more people a chance to see one. d. Because the Moon doesn’t disappear during a lunar eclipse, but turns red, so it’s easier to view.

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10. Why can you point a dish antenna at a geosynchronous satellite without moving the antenna? a. Because the satellite is weightless and just hovers over the same spot on the Earth because gravity doesn’t affect it. b. Because the satellite is exactly halfway between the Moon and Earth and is held there by the gravity of each. c. Because the satellite is in a special orbit which allows it to fall around the Earth at the same rate that the Earth spins. d. Because its omnidirectional signal allows it to broadcast from any location, even the other side of the Earth. 11. The initial motivation for human exploration of space and the landings on the Moon was a. scientific. b. technological. c. economical. d. political. 12. What is the main advantage of remote sensing of the Earth from space? a. It allows global measurements of the Earth rather than just local measurements. b. Sensors are more reliable in the vacuum of space. c. It is easier to make a reliable measurement at a distance than close up. d. Data is more easily transmitted through geosynchronous satellites. (Answer Key: 1.c, 2.b, 3.c, 4.a, 5.b, 6.b, 7.d, 8.b, 9.b, 10.c, 11.d, 12.a)

PART VII SCIENCE, TECHNOLOGY, AND SOCIETY

Chapter 28

THE USES AND APPLICATIONS OF SCIENCE AND TECHNOLOGY IN DAILY LIFE Mary Lightbody

Humans are master manipulators, and since earliest recorded time have developed new technologies that extended their abilities to change the world to ensure their own comfort and survival. The degree of civilization we enjoy was made possible because humans learned how to change energy from one form to another, and how to use energy to do work for us. Starting with fire and the wheel, using simple machines to good effect, and finding new sources of energy, human inventions that improve the quality of life continually emerge. In the recent history of Earth, the impact of humans is considerable, as we gained new knowledge, found new ways to use and modify materials, developed systems to move things from one place to another, and explored places once unimaginable.

ProdUction and transMission of energy Energy is defined as the ability to do work. The forms of energy fall into two categories—kinetic and potential. In the category of potential energy are chemical, gravitational, mechanical, and nuclear energy, because energy in these forms is available to perform work, while those forms in the category of kinetic energy (electrical, thermal, and radiant) are already in motion.

energy ProdUction

Since the first power plants in the United States were developed in the late 1800’s, human use of energy has grown to staggering levels because once energy could be

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transmitted from the site of production to other locations, numerous limits were also removed. Table 28.1 Energy Sources

Energy Source Petroleum Natural Gas Coal Renewable Energy* Nuclear Electric Power

Distribution 36% 24.6% 0.8% 8% 8.4%

* Renewable sources include solar, biomass, wind, geothermal, and water (Total Energy, 2011).

Currently in the United States energy sources vary by region according to availability and the source, but overall the distribution of energy sources can be seen in Table 27.1. Recently interest in, research on, and development of economically feasible renewable energy sources are increasing, because we have such a heavy demand for energy. Currently just under 40% of our energy comes from petroleum, a little over 20% each from natural gas and coal, and under 10% each from nuclear and renewable sources (Total Energy, 2011). The energy generated from these sources is used in four main areas: industry (30%), commerce (18.2%), transportation (27.5%), and electric power generation (24.3%). The energy expended allows us to grow our food, to heat and cool our homes, and to move people and goods around the country. Demand for fuel for transportation is not expected to abate in the United States, given our heavy reliance on personal modes of transport, the layout of our cities, suburbs, and rural areas, our existing infrastructure, and the large distances within our borders. Dependence on oil imports from other countries gives us little control over costs nor continued assurance of its availability. Our own oil reserves have been heavily tapped already; new deposits are more difficult to access, and pose more risks to our environment. Interest in alternative energy sources will continue, but demand is not expected to increase significantly until costs of renewable energy can be reduced. One alternative that has promise is the biofuel industry. In the production of biofuel a plant crop (corn, for example) is ground up into small particles, which are then separated into sugars. The sugars are distilled to make ethanol, which can be used as a fuel additive but usually not as a complete substitute. Currently, ethanol is added to most gasoline at a ratio of 1:9 units across the U.S. Ethanol provides almost 30% less energy per gallon than gasoline, so fuel mixes with higher ethanol content will reduce mileage, and, worse, can damage older engines that were not designed to burn alcohol in any amount. Others decry the decision to use food crops to generate biofuels (such as corn or soybeans), suggesting this has the potential to threaten world food supplies. Still others argue that carbon dioxide is still released to the environment when ethanol fuels are burned, so it still causes environmental damage.

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It is true that the next crop in the fields will reabsorb CO2 molecules, so ethanol production does offer some promise as long as sufficient crop yields are produced each year to meet demands for food and for the biofuel industry. However, should there be weather events that disrupt the growing season, both industries could be impacted. Scientists are conducting research now on alternative plants options that may remove this conflict in the future. Researchers are studying whether seaweed, algae, or alder trees grown in vacant land not suited for field crops would be suitable and efficient substitutes for food crops in ethanol production.

transMission of energy

The source of our energy is not the only challenge related to our insatiable demand for energy. Other difficulties relate to the distribution of electricity and increasing efficiency of the grid. Extensive networks of energy transmission lines cross the United States. The networks (sometimes called the power grid) are largely above ground, and are carried on towers and poles, which put them at risk from natural events like earthquakes, falling tree limbs, or heavy snow and ice loads during weather events. This power grid is thought to be hopelessly outdated, and damage to the system through natural events or human errors has lead to widespread and long lasting power outages. Updating the power grid is becoming a higher priority item for power companies, states, and local municipalities, but engineers are faced with a certain number of constraints, both scientific and economic. For example, electrical power cannot be stored over long periods of time, so production should be metered to suit demand. In addition overloads can cause widespread damage to the grid, and lengthy power outages. Fortunately, upgrading the grid to new “smart grid” technology has started, with computer-based remote control and so called “smart” meters in some locations. These upgraded systems take advantage of two-way communication technology and rely on computer systems to automate much of the process. These strategies increase the efficiency of the energy grid systems, allow early detection and repair of overloaded circuits, and decrease the possibility of (human) error. Workers will no longer need to go house-to-house to read meters, or look for broken equipment; instead, they will be able to make repairs faster and work on modernization efforts. With our increased knowledge and the technical ability to tap into various energy sources come additional challenges. Some scientists have blamed global climate change on the exponential increase in carbon dioxide emissions in the last hundred years, caused by our reliance on burning fossil fuels as an energy source. Other scientists argue that the overall atmospheric temperature has not changed much over the last hundred years and, even if the earth is getting warmer, it is doubtful that carbon dioxide emissions would be responsible for any major changes in the earth’s climate. Nonetheless, the concerns regarding global climate change have affected production costs, because the easiest sources of known

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world oil and gas reserves have been tapped and new sources involve greater costs and increased threats to the environment. Some suggest that nuclear power may be an acceptable alternative, as it does not produce carbon dioxide emissions. In the past fifty years many nuclear power plants have been built around the world. Several different designs exist, but all are potential environmental disasters should earthquakes, tsunamis, fire, human error, or other accidents occur at a nuclear plant. For several decades nuclear power was seen as a reasonable source of electricity across Japan; only now, after the Fukushima plant disaster, are decisions to rely so heavily on nuclear power being questioned in that country and elsewhere. Alternative energy sources (including wind, hydro, tidal, geothermal, and solar) are now being studied by Japanese engineers, with the full support of the government and people of that devastated country. Other countries are assessing their own policies and are balancing the economic challenges against environmental concerns and potential design flaws.

ProdUction, storage, Use, ManageMent, and disPosal of consUMer ProdUcts The old expression about the cart and the horse is not as oblique as one might think. It was the ability of farmers in the 1500s to cut and store hay through the long winters that allowed them to keep and use horses to pull carts and wagons along dirt tracks from the farm to the cities, providing food for the hungry city dwellers. Over time the dirt tracks became roads or train tracks, the carts were replaced with trucks or trains, and horses were relied on to transport freight or people short distances within cities and urban areas until they too were supplanted. The consumer product industry prompted a number of innovations. The development of the compass and navigation tools to calculate latitude and finally longitude allowed ocean transport of goods and products from one continent to another, first with teas and blue and white china to and from Asia, followed by products that could be safely preserved and packaged for ocean voyages. The telegraph was invented, making communication much easier. Another advancement was the introduction of steam power, fueled by coal and petroleum. With the development of these new power plants, textile mills produced enormous quantities of cloth, which in turn lead to ready-made clothes. Paper mills created sufficient supplies of paper for books, newspapers, and mail-order catalogs. Libraries flourished, and public education past sixth grade, especially in the cities, became possible and desirable. As innovation soared, new industries sprouted up, both to make durable goods like cars and washing machines, and to serve the mass market with nondurable goods like towels and household items. Metalworkers created new steels and other alloys for industry and commercial products. Ceramics were developed that were suited for domestic products, industrial purposes, and building materi-

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als. The development of the assembly line and mass production of goods created the supply that consumers wanted, and transportation systems did not lag far behind. At first trains were sufficient to transport goods further and faster. With the invention of the horseless carriage, increasingly efficient systems emerged for the delivery of consumer products further afield. Deliveries required both trucks and an ever-expanding interstate highway system to provide access to places trains did not go. Still later the air industry provided even faster shipments, so food harvested in California or Florida early in the week could be on the table in Minnesota or North Dakota by the end of the week. Fish caught off the coast of Norway could be shipped to China to be filleted, and shipped back to markets in Norway more economically than the fish could be processed by local labor. This threat to local jobs, and the recognition that an increasingly large portion of our food and consumer product costs could be attributed to transportation costs, coincided with the recognition that the health of our environment was being threatened by human activities and our enormous appetite for fossil fuels. While “buy local” has become a more common refrain, echoes of “not-in-my-backyard” cries still can be heard when municipalities try to locate landfills, sewage treatment plants, cemeteries, and recycling centers in settings suitable by geology and land use patterns. Just as humans created the demand for consumer products to increase our quality of life, they also created waste that they no longer wanted. Non-durable items with short life expectancies were sold to the mass market and were thrown away. But where was “away”? Before regulations were put in place, unsightly, toxic, and dangerous trash heaps sprouted in by-ways and back acres. Even in areas where the population recognized the threat to clean water and air, landfills were a necessary part of modern civilization. In time, each city, town, and municipality created landfills for the greater good, to provide a suitable place to dispose of the broken, used up, and otherwise no longer needed items that consumers threw away. Regulations for the management of these sites were put in place to ensure that the engineering designs were followed during construction, that proper maintenance procedures were followed, and that monitoring was continued once the landfills were at capacity. Over time the most ideal sites have been used, as dictated by natural forces such as weather patterns, the location of ground and surface water, and the geology of the site. Now some states ship their garbage to other states, and some dump garbage out at sea. The need for appropriate sites and techniques to dispose of waste will challenge engineers far into the future. New technologies have already started to emerge that reduce waste, offering ways materials can be reused, and finally recycled. The latter aspect is becoming increasingly important, as once abundant natural resources become scarce, and more expensive in their original state.

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ManageMent of natUral resoUrces

Natural resources are substances that have value in their native state; they can be renewable and nonrenewable. Nonrenewables are fossil fuels that took long time periods to form, while renewables can be refreshed, given the proper conditions, weather, and growing seasons. Natural resources occur in different amounts in different geographic locations and are a primary factor both in the ability of a country to produce goods for consumption and export and in the comparative wealth of the country. Japan has very few natural resources aside from fish, must import all the fossil fuels it needs, and consequently has relied on highly efficient technologies and nuclear power to provide electricity for its population. In comparison United States has abundant natural resources, especially if natural resources is broadly defined to include recreational resources that have high aesthetic value. Learning to manage our natural resources with an eye to sustainable practices, increasing efficiency, and reducing waste will be a considerable challenge in years to come. With abundance has come a certain air of arrogance; we currently use and waste more per capita than can be considered a fair share of the natural resources of the world while people struggle for their very existence elsewhere on the globe. Learning to live with less wonted abandon will be better for the country in the long run. We will need new technologies to transmit electricity from its source to the use with less loss, to use materials more efficiently so less enters the waste stream, and to manage the natural resources available on the Earth to raise the economic status, health, and welfare of its people.

nUtrition and PUBlic HealtH issUes There are seven billion people currently eking out a living wherever they are on Earth. Over one billion live in China, another billion live in India. The communist government in China has attempted a number of measures to control its population, including the very controversial one-child policy adopted in 1979. Because these measures have slowed the growth of its population, demographers now predict that India’s population will exceed China’s by 2030. China’s decision has allowed more of its people to have adequate food and housing, although almost half its population lives in huge cities because jobs are more available there. Everywhere in the world there are people who live in better circumstances than others. Some have access to clean water, adequate shelter, and sufficient food for themselves and their children, and some do not. Some have access to excellent medical care, and live long and productive lives. Others live in shantytowns in very close proximity to their neighbors, and fall prey to diseases spread through inadequate sanitation, contaminated water, or through food supplies that are compromised. Among the life-threatening waterborne diseases are typhoid and diarrhea caused by internal parasites, bacteria, and viruses. The contamination of water supplies usually occurs when large populations are crowded into small areas

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that lack provisions for proper sanitation of human bodily wastes. This explains why immediate provisions of fresh water and attention to latrines are the first priorities of Red Cross and other volunteers who converge when natural disasters or local conditions overwhelm a population. In general the public health of citizens in the United States is far better than that of citizens of poor countries whose governments are not stable and are not able to provide for the welfare of the people. In the US people have access to fresh water by turning a tap at home, and can purchase clean and appetizing food at grocery stores located in residential areas. Our water supplies and water treatment systems are extensive; fresh water is precious, but very available and relatively inexpensive. Septic systems and sewage treatment plants collect and treat human waste products and prevent cross contamination of water. Among our natural resources are large areas of land that are well suited for growing food crops, and we have the technology to protect and preserve the food as it is harvested. Bountiful harvests and hungry people living away from the farms create the need for long-term storage of food. Food preservation at first relied on dehydration, smoking, and salting, and took advantage of the cooler temperatures provided in springhouses and root cellars. The discovery of the insulating properties of sawdust allowed people in temperate climates to cut and store ice from the winter months for use in the summer, and icehouses still exist in places across the world. Modern day inventions such as refrigerators and freezers, however, have allowed for safe food storage and decreased incidence of food-borne diseases. In those tropical and sub-tropical areas that still lack refrigeration, animals that are raised for food are sold in markets alive, to be killed, cleaned, prepared, and eaten by the consumer in a relatively short period of time. During food preparation most people in tropical areas learned to add spices and flavors derived from locally available plants; over time these traditions have become an ingrained part of the culture. Only recently have the antimicrobial properties of the spices been studied and valued (Billing and Sherman, 1998). Modern medicine gives us the ability to study what are sometimes called “old-wives tales” to assess their scientific value, but it also gives us the understanding of what causes some of the most debilitating diseases, whether by bacteria or viruses. The dedication of researchers and the advantages provided by new technologies such as the microscope, and the unraveling of genetic code, have allowed many drug therapies to evolve. These modern drugs and access to immunizations have removed the most frequent causes of death in many areas, have totally eradicated some diseases, and have extended life expectancies in areas where modern medicine has reached sufficient percentages of the population. When access to modern medicine is more difficult to achieve, advances in health are also challenged. With time and education, both of which can be enhanced through technology, it is hoped that nutrition and public health will also advance to those most hampered by economic, social, and political conditions.

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agricUltUral Practices Because modern practices have also advanced to farm fields, through the mechanization of farms, the availability of combine harvesters, and the use of modern and often sophisticated animal husbandry techniques, the world no longer faces food shortages. Modern technologies have also advanced to the farm fields. Farmers now drive around their fields with air conditioned cabs, equipped with Global Positioning Systems (GPS) and onboard soil analysis technologies, and deliver proportional amounts of fertilizer and soil additives to adjust the pH to optimal levels in targeted and specific locations. Many farm tractors now have automatic steering, which prevents overlaps, and overcomes the fatigue farmers used to suffer when planting fields 12-14 hours a day. With better information on weather conditions, farmers are better able to manage weather risks, and have better harvests as a result. Genetically modified seeds can be planted simultaneously with herbicides, so only the desired plants grow in large acres of monoculture. Irrigation systems are increasingly sophisticated as well. What is not clear is whether the reliance on chemical fertilizers is beneficial, either to the land or to the people who consume the crops. Many prefer organic foods, which are grown with natural fertilizers and with only natural agents against insect pests. In some areas, organic food growers are subject to the same food quality inspections as are their larger and more chemical dependent neighboring farm growers. In other areas of the country less regulation and inspection occurs. It may not be possible to determine the conditions in which meat chickens were raised, or eggs were produced for market, even though an organic label has been put on the meat or the eggs. Not all the problems related to food production and supply have been solved. Whether there are any adverse health effects caused by the consumption of genetically modified foods deserves further research. No one would want to provide food that added to the health risks of the consumer because this may be a case of needing more information to make an informed decision. What we do face are inadequate delivery systems, intransigent governments, and countries torn apart by war. In these circumstances food deliveries are difficult to maintain. The World Health Organization is prepared to step in, but may only go where invited. Even in the United States, with its large farms, and ample food supplies, there are people who go hungry because economic conditions are desperate.

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review QUestions—cHaPter 28 1. What percentage of energy in the United States currently comes from fossil fuel sources? a. 40% b. 60% c. 80% d. None of the above. 2. The energy grid in the United States is outdated. Which of the following is NOT a problem associated with this reality? a. Smart meters have a negative impact on efficiency and energy savings. b. Electric meters have to be read by a person traveling from residence to residence. c. Human error has caused widespread power outages. d. Power lines on towers above ground level are at risk from weather events. 3. Learning to manage our natural resources is key to sustaining life as we know it. Here are four options that may or may not contribute to a productive future: (1) increase the use of plastics as packaging materials, (2) reduce the amount of materials that enter our waste stream, (3) develop new technologies to manage our use of natural resources, and (4) allow nations with abundant natural resources to regulate prices. Which of these could be combined to support greater sustainability? a. 1 and 2 b. 2 and 3 c. 3 and 4 d. 4 and 1 (Answer Key: 1.c, 2.a, 3.b) Works Cited AAAS Atlas of Population and Natural Resources. “Population and Natural Resources: Energy”. American Association for the Advancement of Science. Accessed October 25, 2011. http://atlas.aaas.org/index.php?part=2 Billing, Jennifer and Sherman, Paul W. 1998. “Antimicrobial Functions of Spices: Why Some Like it Hot.” Quarterly Review of Biology 73:3-49. Total Energy. U.S. Energy Information Administration. Accessed October 25, 2011. http://www.eia.gov/totalenergy/.

Chapter 29

THE SOCIAL, POLITICAL, ETHICAL AND ECONOMIC ISSUES ARISING FROM THE USE OF CERTAIN TECHNOLOGIES Brendan Callahan

In many ways, this chapter differs from many that appeared earlier in the book. There are no difficult concepts or formulas to memorize. The best preparation for answering Science-Technology-Society (STS) questions is an understanding of contemporary societal issues that deal with science. Two areas of particular importance are those that deal with the medical field, and those that deal with human impact on the environment. The fully prepared science teacher has an understanding of multiple perspectives on these topics, backed by a strong understanding of scientific knowledge. The best sources are reputable newspapers and news reports free from the opinion that is popular in today’s media.

cloning, Prolonging life, and Prenatal testing cloning

Although most people probably think of reproduction when they hear the word “cloning,” there are actually three different types of cloning, each with different processes and goals, and hence different ethical issues. The three types of cloning are recombinant (DNA) cloning, reproductive cloning, and therapeutic cloning (Human Genome Project 2009). Recombinant (DNA) cloning is a process in which a segment of DNA (a gene) is inserted into another cell in order to make copies of the gene. This technology has at least two different applications. The first application is in the bio-

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medical field in order to potentially cure genetic disorders. If a corrected copy of a gene could be inserted into a patient’s cells in place of the defective gene, then theoretically the disorder would be cured. A second application is in the development of genetically modified foods and organisms (GMF/GMO). Potential benefits would be foods with improved taste or nutrition, or better adaptations to harsh conditions. Reproductive cloning hit headline news when it was announced that “Dolly” had been born through a process called cell nuclear transfer (SCNT), which involves the transfer of genetic information into an egg with the genetic material removed. The egg with the new DNA is chemically or electrically stimulated to promote development. Once the embryo is of a suitable size, it is inserted into the uterus of a female host where it develops until birth. Since 1996, many different animals have been cloned, including sheep, goats, cows, mice, pigs, cats, and rabbits. The use of reproductive cloning has the potential to repopulate endangered animals in cases where other methods have not been successful. Giant pandas are one instance that may be familiar to most people. While there may be potential benefits to cloning animals, the process is expensive and inefficient, with a 90% failure rate. Additionally the cloned animals tend to have compromised immune systems, and often die at an earlier age than their wild type peers. Although there is some outcry over the cloning of animals, the more contentious issue is the cloning of people. The American Medical Association and the American Association for the Advancement of Science have both come out against human cloning. Many states have laws that restrict or prohibit reproductive or therapeutic cloning (National Conference of State Legislatures 2008). Therapeutic cloning is the production of human embryos for research purposes. Therapeutic cloning is also known as “embryo cloning” and “stem cell research,” since the focus of therapeutic cloning is the harvesting of stem cells from human embryos. During this process the embryos are destroyed, which raises ethical concerns to people opposed to abortion. Therapeutic cloning has the potential to replace damaged cells and tissues damaged by disease, such as heart disease, Alzheimer’s, cancer, and Parkinson’s. Some people believe that therapeutic cloning could lead to the production of whole organs for transplant purposes as well.

Prolonging life

Any discussion of prolonging life should center on what it means for a human to be alive. Previously, a heartbeat and breathing were benchmarks for living. However with current technology, machines are able to carry out these functions for people. Heart-lung machines and kidney dialysis machines provide many of the essential functions needed to keep a patient alive. Most doctors use brain activity to distinguish the living from non-living. Much of the contemporary debate centers around the ending of life, known as euthanasia. Those in favor of euthanasia believe that terminally ill people have a right to die with dignity and to avoid

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prolonged suffering. Those against euthanasia believe it is the doctor’s responsibility to keep the patient alive as long as possible, and also believe there could be a slippery slope leading to involuntary euthanasia, or the murder of patients for reasons other than the patient’s benefit. There are two types of euthanasia, passive and active. Passive euthanasia is generally known as the withholding of medical treatment and allowing the person to die on his or her own. There are many right-to-life groups, including the Catholic Church, that oppose any attempts to prematurely end a person’s life. However, passive euthanasia is currently legal in all 50 states. Active euthanasia, sometimes referred to as “physician-assisted suicide,” or “mercy killing” is the deliberate ending of life, typically through lethal injections. Oregon was the first state in the United States to allow physician-assisted suicide, and Washington currently (as of September 2011) allows the practice. In many instances, the question whether to prolong life or end it is controversial because different family members may disagree about what the patient would want. Two devices used to describe the patient’s wishes are living wills and Do Not Resuscitate (DNR orders). A living will describes how a person wants to be treated in life-sustaining situations, such as a terminal condition or accident. The living will can describe which technologies can be used to prolong life, and in which instances they should be used. A DNR order is a refusal of CPR or electric shock treatment should the person’s breathing or heart stops. In instances where the potential risks of CPR are greater than the benefits, such as with terminally ill patients, it may make sense to have a DNR order.

Prenatal testing

Prenatal testing can alert expectant parents to genetic abnormalities prior to the baby’s birth. These genetic abnormalities include Down’s Syndrome, spina bifida, Tay Sach’s disease, and cystic fibrosis. Right-to-life groups may oppose prenatal testing that provides information that might be used to promote abortion as an option. Three of the most invasive testing procedures are amniocentesis, chorionic villus sampling, and cordocentesis. These invasive procedures might be done after prescreening has indicated a potential problem or genetic defect with the baby. Amniocentesis is the removal of a sample of amniotic fluid around the fetus, usually following the 15th week of pregnancy. This fluid contains cells that are genetically identical to the growing fetus, and may be tested for genetic disorders such as Down’s Syndrome and spina bifida. The amniotic fluid may also be tested to determine the maturity of the lungs in preparation for a planned delivery, particularly when the delivery will result in a premature birth. Women most likely to have an amniocentesis would include those with an abnormal screening for a genetic disorder, those with a chromosomal defect in a prior pregnancy, women 35 and older, and those with a family history of a genetic condition, or when they or their partner is a known carrier of a genetic condition. Some risks associated with amniocentesis include miscarriage, cramping and vaginal bleeding, needle injury

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to the fetus, the leaking of amniotic fluid, infection, or transmission of infection or Rh sensitivity between the baby and mother (Mayo Clinic “Amniocentesis” 2010). Chorionic villus sampling can be done between the tenth and twelfth week of pregnancy, which is earlier than amniocentesis. In this procedure, projections from the placenta are removed with a needle. The placenta has the same genetic information as the baby. The purpose of the procedure is the same as amniocentesis, which is to determine chromosomal abnormalities. The risks are similar to amniocentesis and include miscarriage, cramping, and vaginal bleeding, Rh sensitization and infection (Mayo Clinic “Chorionic villus sampling” 2010). Cordocentesis, or Percutaneous umbilical cord blood sampling, is when a sample of the fetus’ blood is removed from the umbilical cord during pregnancy. This procedure is usually done following the eighteenth week of pregnancy or later due to the increased risks, which include miscarriage, bleeding, the slowing of the baby’s heart rate, and infection. One advantage to cordocentesis is that blood disorders, such as anemia, sickle cell disease, and Rh incompatibility can be determined in addition to the chromosomal disorders found by amniocentesis and chorionic villus sampling (Mayo Clinic “Cordocentesis” 2010). While few people oppose these practices directly, many people are concerned with the repercussions of genetic testing. Right-to-life groups would certainly be opposed to genetic testing that leads to the abortion of fetuses, and many people worry about the development of “designer babies,” in which each of the baby’s traits is determined by the parents, including sex. Although genetic testing is currently legal in the United States, states differ in abortion laws and the question of which services are covered under insurance will continue to be negotiated, due to the related costs.

tHe iMPact of science and tecHnology on tHe environMent and HUMan affairs fossil fUels and alternative energy

Coal, oil, and natural gas are the three types of fossil fuels most commonly used in the United States at the present time. Fossil fuels are named because they are formed from organic materials (plants and animals) that have typically decayed years under intense heat and pressure. They are considered nonrenewable resources, since they typically take extremely long periods of time to form. While fossil fuels produce approximately 68% of the electricity for the United States, they also produce the most pollution. Coal is mined either from the surface or underground. Coal burning produces carbon dioxide, sulfur dioxide, nitrogen oxides, and mercury compounds. Further emissions from the mining, cleaning, and transportation of coal can also occur. Water pollution can occur when coal power plants use water for steam production and cooling, which is then released back into the water. Also the water run-off

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when rain washes over coal piles can contain heavy metals that pollute water supplies. The burning of coal produces a solid waste called ash, which contains metal oxides. The soil around coal mines and coal power plants often become polluted as well, and these effects continue long after the power plant or mine closes. Surface mines have larger implications for land degradation than underground mines (EPA “Coal,” 2007). Natural gas is gathered from underground wells and sent to treatment plants to be converted into a usable form. The burning of natural gas produces nitrogen oxides and carbon dioxide, but in smaller amounts than coal or oil. Methane can also be produced when incomplete combustion takes place. There are fewer issues with water pollution or solid waste than coal or oil as well. Land degradation can occur at extraction sites and from the construction of power plants. These areas can also contain areas of habitat loss for plants and animals (EPA “Natural Gas,” 2007). Oil is gathered from underground sites either on land or in the water. The burning of oil produces nitrogen oxides, sulfur dioxide, carbon dioxide, methane, and mercury compounds. Oil wells also produce large amounts of methane as the machinery used to extract oil runs on natural gas or diesel fuel. Large amounts of water are used for steam production and the cooling of machinery, and this water is sometimes returned to the environment in a polluted state and at a higher temperature, which can affect aquatic plants and animals. The refining process produces sludge, a solid waste product that contains high levels of metals and toxins. Power plant construction destroys habitats for plants and animals, and waste products also contaminate the environment (EPA “Oil,” 2007). Oil spills can also have large impacts on the environment, as the 1989 Exxon Valdez spill off the coast of Alaska (10.8 million gallons spilled), and the 2010 Deepwater Horizon spill off the coast of Louisiana (205.8 million gallons spilled) have shown (Repanich, 2010). The largest source of energy other than fossil fuels is nuclear power at 20.3%. Nuclear power is produced by bombarding atoms of uranium with neutrons in order to split the uranium atoms (a process called nuclear fission). This splitting of the atoms results in the release of energy used to make steam. While nuclear power does not create greenhouse gases or air pollutants like fossil fuels do, there is the potential for radiation to be transmitted over long distances through the air. Nuclear power also requires large amounts of water to operate, both in the production of steam and cooling of machinery. The water does not come into contact with the uranium, and is therefore not radioactive. However, the water returned to the environment is often a higher temperature than when removed, which could affect aquatic plants and fishes. Nuclear power does create radioactive waste, which is generated from the spent uranium pellets used by nuclear reactors. These used uranium pellets are packaged in steel-lined containers inside concrete and steel vaults. The used fuel is typically stored at the nuclear power plant, although future discussions will certainly center on where to store the spent uranium pellets (EPA “Nuclear Energy,” 2010).

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Other renewable sources of energy include hydroelectric, solar, wind, and geothermal energy. Typically these forms of energy have less impact on the environment than fossil fuels and nuclear power. However, at this point the infrastructure supports the production of fossil fuels because the cost to build the infrastructure for alternative fuels will be high, and decisions will need to be made regarding who will pay for these structures in the future.

cliMate cHange

The term “climate change” is preferred over the term “global warming” because change refers to precipitation and wind changes, in addition to temperature. Climate change is caused by natural factors, such as volcanic eruptions, changes in the Earth’s orbit, and changes in solar energy. Human activities may also influence climate change, due to the production of greenhouse gases by burning coal and oil. Although many climatologists agree with the concept of climate change, there are others who are outspoken against the concept (Wolchover, 2011). Those who dispute the concept of rapidly occurring climate change caused by carbon dioxide emissions tend to use the following arguments: (a) that most of the fluctuations in global temperature are natural and/or (b) that the measurements taken to support the climate change model are flawed.

conclUsion

Ultimately, there are many STS concepts that could appear on the state proficiency tests. A good base knowledge of science and an understanding of multiple perspectives regarding contentious issues will help the science teacher be successful on the exam and in the classroom. In addition to reading this book, it is highly recommended that teachers make a practice of reading a national level newspaper daily.

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review QUestions—cHaPter 29 1. Which of the following is NOT an example of cloning? a. Recombinant cloning. b. Reproductive cloning. c. Stem-cell cloning. d. Therapeutic cloning. 2. Therapeutic cloning is defined as which of the following? a. A process in which a segment of DNA is inserted into another cell to make copies of the gene. b. The production of human embryos for research purposes. c. The transfer of DNA into a reproductive egg, which has had its genetic material removed. d. The insertion of a gene into an organism’s DNA in order to cure a genetic disease. 3. Which of the following is an argument used by proponents of euthanasia? a. People have the right to die with dignity. b. Doctors should keep patients alive as long as possible. c. The legalization of euthanasia could lead to the involuntary murder of patients unable to defend themselves. d. All of the above statements are made by proponents of euthanasia. 4. Which of the following is NOT an example of a method of prenatal testing? a. Amniocentesis. b. Chorionic villus sampling. c. Cordocentesis. d. Genetic engineering. 5. Cordocentesis is defined as which of the following? a. The process of removing a sample of the fetus’ blood from the umbilical cord during pregnancy. b. The process of removing a sample of amniotic fluid from the placenta. c. The process of splicing a section of DNA into the umbilical cord. d. The process of sampling a section of the placenta during pregnancy. 6. Which of the following is NOT true of fossil fuel energy? a. Water pollution can occur during the burning of fossil fuels. b. The mining of fossil fuels can lead to land degradation. c. Water pollution can occur when oil refineries leak oil. d. The burning of fossil fuels has very little effect on air quality.

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7. Which of the following is NOT accurate? a. Renewable energy sources produce large amounts of air and water pollution. b. Renewable energy sources have a large impact on land degradation. c. The infrastructure is not developed for renewable energy in the United States. d. The cost of containing alternative fuels is prohibitive at this time. (Answer Key: 1.c, 2.b, 3.a, 4.d, 5.a, 6.d, 7.c) Works Cited Energy Information Administration. “Electricity.” Last modified April 2011. http://www.eia.gov/cneaf/electricity/epa/epa_sum.html Environmental Protection Agency. “Climate Change: Basic Information.” Last modified April 14, 2011. http://www.epa.gov/climatechange/basicinfo.html -- “Coal.” Last updated December 28, 2007. http://www.epa.gov/cleanenergy/energy-and-you/affect/coal.html -- “Natural Gas.” Last updated December 28, 2007. http://www.epa.gov/cleanenergy/energy-and-you/affect/natural-gas.html -- “Nuclear Energy.” Last updated March 8, 2010. http://www.epa.gov/cleanenergy/energy-and-you/affect/nuclear.html -- “Oil.” Last updated December 28, 2007. http://www.epa.gov/cleanenergy/energy-and-you/affect/oil.html Human Genome Project Information. “Cloning Fact Sheet.” Last modified May 11, 2009. http://www.ornl.gov/sci/techresources/Human_Genome/elsi/cloning.shtml Mayo Clinic. “Amniocentesis.” Last modified May 15, 2010. http://www.mayoclinic.com/print/amniocentesis/MY00155METHOD=print&DSE CTION=all -- “Chorionic villus sampling.” Last modified May 15, 2010. http://www.mayoclinic.com/print/chorionic-villus-sampling/MY00154METHOD= print&DSECTION=all -- “Cordocentesis.” Last modified July 23, 2010. http://www.mayoclinic.com/health/percutaneous-umbilical-blood-sampling/ MY00147/METHOD=print National Conference of State Legislatures. “Human Cloning Laws.” Last updated January, 2008. http://www.ncsl.org/default.aspx?tabid=14284 Repanich, J. “The Deepwater Horizon Spill By the Numbers.” Last modified August 10, 2010. http://www.popularmechanics.com/science/energy/coal-oil-gas/bp-oil-spill-statistics Wolchover, N. “Why Climate Change Skeptics Remain Skeptic.” Last modified November 22, 2011. http://www.cbsnews.com/8301-205_162-57329755/why climate-change-skeptics-remain-skeptical/

ABOUT THE AUTHORS Richard J. Batt earned his PhD in geology from the University of Colorado. Dr. Batt is an associate professor in Earth Sciences at Buffalo State College, teaching undergraduate and graduate courses on geologic topics including Earth history, the geology of various regions, paleontology, and dinosaurs. His primary interests have been in paleontology, stratigraphy, ancient environments, hydrogeology, modern mollusks, dinosaurs, and regional geomorphology. He has been published in the journals Lethaia and Palaios, field trip guidebooks for geological organizations, The Monograph (a Canadian journal of geography education), Interaction (Geography Teachers’ Association of Victoria, Australia), and Kansas English. He collaborates with Dr. Robin Harris in workshops, public presentations, and publications on educational topics including the nature of science, dinosaurs, seashells, and areas of geologic and scenic interest including Hawai`i, the Galápagos Islands, Colorado, Alaska, and Iceland. Currently he is writing a book on the geologic history of Niagara Falls and its gorge. He can be contacted at [email protected]. David Buckley earned his PhD in Astronomy and MS in Physics from the University of Massachusetts at Amherst. Dr. Buckley is a professor in the Physics Department at East Stroudsburg University in Pennsylvania, where he teaches undergraduate courses in astronomy, physics and astrophysics. His primary research interests have been in the death of low and medium mass stars and their remains-planetary nebulae. He is also the coordinator of the McMunn Planetarium at ESU and runs the planetarium’s outreach program for schools and community groups. He can be contacted at [email protected].

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Patricia Bricker earned her EdD in teacher education from the University of Tennessee and is currently an associate professor of science education in the Elementary and Middle Grades Education program at Western Carolina University. Her research interests include inquiry-based science education, integrated curriculum, experiential education, and teacher professional development. Her work has been published in journals such as Science & Children and Science Scope and she has served as principal investigator on science education grants focused on teacher professional development. Dr. Bricker is currently leading a preservice teacher education Farm to School project. She began her career as an environmental educator and taught both elementary and middle school prior to becoming a teacher educator. She can be contacted at [email protected]. Brendan E. Callahan earned his Ph.D. in Curriculum and Instruction with an emphasis in science education from the University of South Florida. Dr. Callahan is an assistant professor of biology education in the Biology and Physics Department at Kennesaw State University, where he teaches physical science for elementary teachers as well as science content and pedagogy classes at the graduate level. His primary research focus is the use of socioscientific issues in secondary science classrooms, with an emphasis on how students think and communicate about these issues. He has published in the Journal of Research in Science Teaching and has received awards for his teaching at the secondary level. He can be reached at [email protected]. G. Nathan Carnes earned his PhD in education administration with an emphasis in science education from Miami (Ohio) University. Dr. Carnes is an associate professor of science and middle level education within the Department of Instruction and Teacher Education at the University of South Carolina, where he teaches undergraduate and graduate science methods courses within elementary, middle level, and secondary degree programs. His primary research interests are in elementary and middle level science teacher preparation, inquiry-oriented instruction, and classroom management. He has published in the International Encyclopedia of Education, Journal of Women and Minorities in Science and Engineering, Teaching and Change, and contributed chapters to Association for Science Teacher Education monographs. He has received honors for his teaching at the university level that include the Association for Science Teacher Education Outstanding Science Teacher Educator of the Year, Category I. He can be contacted at [email protected]. Robert A. Cohen is a professor of physics at East Stroudsburg University of Pennsylvania in East Stroudsburg, Pennsylvania. He received his Bachelor’s Degree in meteorology from the Pennsylvania State University in 1985. He received his Master’s and PhD degrees in physics and atmospheric science from Drexel University in 1988 and 1993 respectively. He also earned a Master’s in Education from Temple University in 1991 through which he earned teaching credentials in secondary math and science. Dr. Cohen’s research in meteorology focuses on the structure of occluded extratropical cyclones, using numerical simulations to identify the evolution of airstream boundaries within the storm. He is also actively in-

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volved in science teacher preparation and physics education. He can be contacted at [email protected] John K. Elwood earned his PhD in physics from the California Institute of Technology. He is an associate professor of physics in the Physics Department at East Stroudsburg University in Pennsylvania, where he teaches a wide array of undergraduate physics courses. His primary research interest is theoretical highenergy physics, with emphases on CP violation and theories beyond the Standard Model. Dr. Elwood also has an interest in fostering opportunities for undergraduate research, and has involved students in projects that studied high-altitude cosmic rays and that characterized polymers. He has been published in Physical Review Letters, Nuclear Physics B, Physical Review D, Physics Letters B, AMS/IP Studies in Advanced Mathematics, and in a monograph from the Collaborative for Excellence in Teacher Preparation in Pennsylvania. Dr. Elwood has an abiding interest in teacher preparation in science, and was involved in the design of an inquiry-based science course for elementary and mid-level pre-service education majors at East Stroudsburg University. He may be contacted at jelwood@po-box. esu.edu. Robin L. Harris earned her PhD in Science Education from the University of Iowa. Her MEd. was in Teaching and Curriculum from the University of Pennsylvania, Harrisburg Campus. Dr. Harris is an associate professor in Science Education at Buffalo State College, where she teaches undergraduate and graduate science methods, research and general science courses. Her primary research interests are in conceptual change, constructivist teaching and assessment, and inquiry-orientated instruction. She published three books, one co-authored; Science and Writing Connections, Open-ended Questions: A Handbook for teachers and Teaching with Purpose: Closing the Research-Practice Gap. She has also been published in Science Scope, Kansas English, The Clearing House and Science Activities. She was the project leader on a ten year funded project titled, The Buffalo Science Teachers’ Network. Sponsored by Eisenhower and then TLQP funds, this project was a virtual and real professional development school matrix made up of 30 schools, science and special education faculty in the Buffalo Public School system. She collaborates with Dr. Batt on several Earth Science and Science Education programs, projects and publications. She can be contacted at [email protected] James C. Hunt earned his PhD in biology from the University of California, Los Angeles. Dr. Hunt is an associate professor in the Biology Department at East Stroudsburg University, where he directs the Marine Sciences Program. He teaches undergraduate and graduate courses in oceanography, marine biology, and several field classes focused on marine ecology. His research interests center on exploring the ecology of the deep sea and coral reef ecosystems. He has published articles in several national and international journals, and he regularly collaborates with researchers from Japan, Europe, and Australia. He is the author of one book for the general public and his research has been featured in newspapers, television documentaries, and the journal Science. He can be contacted at [email protected].

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Vanessa L. Hunt earned her Ph.D. in Curriculum and Instruction (Biology Education) from Louisiana State University and is currently a professor of science education within the College of the Sciences at Central Washington University. She is director of CWU science education programs in the greater Seattle area, and also teaches a variety of undergraduate interdisciplinary science and biology courses. Her research interests in science education include community based learning in environmental science education, marine science education, and the interface of informal and formal science education. She may be contacted at [email protected]. Adam T. Johnston holds a PhD in science education from the University of Utah, where he also earned his MS in physics. Dr. Johnston completed a BS in physics from Lewis & Clark College in Portland, OR. Currently, he is at Weber State University, a professor of physics and associate director for science teacher education in the College of Science. His scholarship in student and teacher conceptions of science has been published in journals such as the American Educational Research Journal, Science Education, and the Journal of Science Teacher Education. He is most proud of the contributions he has made to create and cohost Science Education at the Crossroads (sciedxroads.org) and the development of a variety of programs for children and teachers. You may contact Dr. Johnston at [email protected]. T. Michelle Jones-Wilson earned her PhD in Chemistry from Washington University in St. Louis and was a NBLI-post doctoral Fellow at Mallinckrodt Institute of Radiology and Children’s Hospital of St. Louis. Dr. Jones-Wilson is currently an Associate Professor of Chemistry and Director of the Programs in Biological Chemistry at East Stroudsburg University in Pennsylvania. She teaches a broad range of science major’s courses and general education courses in chemistry. Her current research focuses on development of curriculum for upper-level undergraduate biological chemistry laboratories and development of methods for teaching standard laboratory protocols. She has been published in the Journal of Nuclear Medicine, Radiopharmaceutical Chemistry, the Journal of Chemistry Education, and the Journal of College Science Teaching. Her methods for teaching problem solving in undergraduate science classes have been featured in The Chronicle of Higher Education. She can be contacted at [email protected]. edu. Kenneth P. King earned his EdD in curriculum and instruction from Northern Illinois University. Dr. King is a professor of education in the Department of Curriculum Studies at Roosevelt University in Schaumburg, IL, where he teaches graduate and undergraduate coursework in science education. His research interests are in the areas of history of science education and in developing inquiry-rich teaching materials using inexpensive household materials. He has been published in Science Scope, Science Education and The Journal of Science Education and Technology. He is also the author of two books on science teaching. He can be contacted at [email protected].

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Maria Kitchens-Kintz earned her PhD in Cellular/Molecular/Genetics from the University of South Carolina. Dr. Kitchens-Kintz is a professor of biology in the Biological Department at East Stroudsburg University in Pennsylvania. She teaches both undergraduate and graduate level classes, including Introduction to Biotechnology, Molecular Biotechnology, and Cell Culture Techniques. Her research interests include cytotoxicity testing of commercially available green teas using human colon cancer cells, and applying molecular based techniques for monitoring deer mice populations in the Delaware Water Gap Recreational Park. Her latest project, funded by an ESU Presidential grant, uses the polymerase chain reaction techniques to identify microbial populations in the rhizosphere of the invasive plant Phragmites australis along the Brodhead Watershed. The data from this project will contribute to local and state management plans designed to control the spread of this invasive species in Pennsylvania. She can be contacted at [email protected]. Martha J. Kurtz earned her PhD in Curriculum and Instruction from Arizona State University. Dr. Kurtz is a professor of Chemistry and Science education at Central Washington University (CWU) in Ellensburg, WA, where she also serves as the Science Education Department Chair and the Director of the CWU Center for Excellence in Science and Mathematics Education. She teaches undergraduate and graduate science education methods courses, interdisciplinary science content courses for future teachers and has taught introductory chemistry in the past. Her research interests are in exploring teaching pedagogies that increase critical thinking skills and in using the environment as a context for integrated learning in K-16 classrooms. Community-based inquiry is a recent focus combining both interests. She has been published in the Journal of College Science Teaching, Cell Biology Education-Life Science Education, and the Journal of Chemical Education. As department chair she implemented the first middle level mathematics and science pre-service teacher program in Washington State. She leads the National Science Foundation (NSF) funded CWU Robert Noyce Scholarship Program and was a lead team member on the NSF:GK-12 WATERS (Watershed Activities To Enhance Research in the Schools) program. WATERS brought teams consisting of a graduate student, a middle or high school science teacher, and a faculty mentor together to facilitate authentic research in the schools. Dr. Kurtz can be reached at [email protected]. Mary Lightbody holds two graduate degrees from The Ohio State University, an M.Ed and a Ph.D. in Mathematics, Science, and Technology Education, and a BA from Harvard. Dr. Lightbody is an assistant professor at The Ohio State University, Newark campus, where she teaches graduate and undergraduate science methods and science education classes in the College of Education and Human Ecology, School of Teaching and Learning. A former middle school science teacher in the Columbus City Schools, she also has validation in K-12 gifted education, and she became a National Board certified teacher in Early Adolescence Science in 2000. Always a techie herself since early experience writing code for web sites in the early 90’s, Dr. Lightbody continues to be interested in ways technology

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can be used to help students learn content that is difficult to teach and/or learn, and she conducts research on the many ways teachers are able to differentiate their instruction to meet their students’ needs. She has been published in the Science Teacher and Science Scope, served as the President of the Science Education Council of Ohio in 2004-05, and was elected as the District X Director for the National Science Teachers Association (NSTA), representing Indiana, Michigan, and Ohio from 2006-09. William M. Loffredo earned his PhD in biochemistry from The Ohio State University. Dr. Loffredo is a professor of Chemistry at East Stroudsburg University in Pennsylvania, where he teaches undergraduate courses and maintains the departmental NMR instrument. His primary research interests are in bioorganic syntheses and NMR studies of biological molecules. He has also been involved in writing undergraduate chemistry laboratory experiments to be used in general, organic and biological chemistry curricula. Dr. Loffredo enjoys collaborating with various faculty members from the Departments of Education and Nursing to enhance their programs using his course offerings. Dr. Loffredo has also been invited to collaborate on various faculty grants both at the local and national levels. He can be contacted at [email protected]. B. Patricia Patterson earned her EdD. in Education and her Masters in Botany from the University of Maine at Orono. Dr. Patterson is a professor of Education at Wesley College in Dover, Delaware where she teaches undergraduate science and mathematics courses and graduate education courses. Her primary research interests are in development of methods and strategies that promote teachers’ mathematic and scientific literacy and in the use of Gowin’s Vee for creating and analyzing instructional plans. Her work has been published in Science Scope and The Journal of the Maine Audubon Society. She has contributed two chapters to published books on the teaching of reflection. Through a variety of grants she established an on-campus charter school and Boys and Girls Club. She served on the Delaware Department of Education task force for writing the Delaware Teacher Standards and contributed instructional plans and concept maps of the state content standards to Department of Education publications. She can be reached at [email protected]. Anton Puvirajah, a former high school science teacher, is an Assistant Professor of Science Education at Georgia State University. He completed his undergraduate studies at the University of Manitoba and received his PhD in Curriculum and Instruction from Wayne State University. His research interests include examining scientific reasoning and the nature of the learning environment that facilitates meaningful science talk and reasoning. Within this paradigm he is currently studying how teachers and students examine and make sense of their personal epistemological stances related to science ideas. Dr. Puvirajah also does research on teacher embodiment, reflective practice, and community building, and the efficacies of using information and communications technology (ICT) tools for this purpose. In addition to conducting research, he teaches both undergraduate and graduate courses in K-12 Science Teacher Certification programs

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and graduate research courses in Teacher Education. He has received funding from the National Science Foundation and the Georgia Department of Human Services to work with teachers and students. Dr. Puvirajah works closely with his graduate students in designing project-based science curricula for after schools and summer programs, and conducts professional development workshops for area science teachers. He can be contacted at [email protected]. Peter Rillero earned his PhD in science education from The Ohio State University. Dr. Rillero is an associate professor of education in the Mary Lou Fulton Teachers College, Tempe AZ, where he teaches graduate and undergraduate coursework in science education. His research interests are in the areas of history of science education, inquiry, student research, and technology. He has been published in Science Scope, Science and Children, School Science and Mathematics, Science Activities, Electronic Journal of Science Education, Studies in Science Education, Electronic Journal of Literacy through Science, The Science Teacher, Journal of Computers in Mathematics and Science Teaching, Journal of College Science Teaching, The American Biology Teacher, Journal of Technology and Teacher Education, and the Journal of Science Teacher Education. He is also the author/co-author of more than thirty books in science education. He can be contacted at [email protected]. Kim Cleary Sadler is an associate professor of biology and co-director for the Center for Cedar Glade Studies at Middle Tennessee State University, located in Murfreesboro, Tennessee. She teaches undergraduate non-majors biology courses in general education and pre-service teacher education, in addition to graduate courses in the Math and Science Education doctoral program. Dr. Sadler serves as PI and co-PI on two National Science Foundation grants. One is related to after school STEM experiences with middle school students and the other is a GK-12 project where graduate student scientists spend a year in a high school classroom. When not collaborating with colleagues about strategies to teach large biology classes effectively, she is also interested in research questions that address K-12 learning outside the classroom. She has published in American Biology Teacher, Journal of College Science Teaching, Journal of Elementary Science Teaching, chapters in NSTA Monograph’s on Exemplary Teaching in K-4 and Informal Settings, and chapters in The Inclusion of Environmental Education in Science Teacher Education. Dr. Sadler can be contacted at [email protected]. Christine Schnittka earned her PhD in science education from the University of Virginia, and degrees in mechanical engineering from Auburn University and the University of Virginia. Dr. Schnittka is an assistant professor of science and engineering education at Auburn University where she teaches secondary science education and conducts research on K-12 science and engineering teaching and learning. She helps direct the NSF-funded afterschool program, Studio STEM, which brings her technology-infused science and engineering curriculum to rural afterschool programs. Her work has been published in the International Journal of Science Education, the International Journal of Engineering Education, the Journal of Pre-College Engineering Education Research, Advances in Engineer-

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ing Education, Science and Children, Science Scope, and The Science Teacher. She can be contacted at [email protected]. C. Matt Seimears grew up in Kansas where he earned all four of his college degrees. He taught in Wichita, Kansas USD 259 before earning a Ph.D. in curriculum and instruction from Kansas State University in 2007. He has been on the faculty of Emporia State University since 2004, teaching science methods courses and advising graduate students. Dr. Seimear's research interests include the following: personal epistemological development of in-service teachers of science, English language learners' understanding of science, and the effects of constructivist-based teaching strategies on English language learners in science classrooms. Dr. Seimears is an active member of The National Association for Research in Science Teaching, The American Association for the Advancement of Science, The National Science Teachers Association, and he serves as a curriculum developer and consultant for PITSCO Education. He is also the contact person for the Elementary Education Robotics program. Dr. Seimears was honored as Newman University's Outstanding Leon A. McNeill Alumni of the Year Award in 2010. He can be contacted at [email protected]. Cindi Smith-Walters earned her PhD in environmental science from Oklahoma State University and she also holds degrees in curriculum and instruction, and biology. Currently a professor in the biology department at Middle Tennessee State University, she co-directs the MTSU Center for Environmental Education and teaches a content course “Life Science for Elementary Teachers” as well as Environmental Problems, and Inquiry in the Laboratory and Schoolyard. Dr. Smith-Walters is particularly interested in the use of the schoolyard and the out-of-doors as it relates to teaching and learning in people of all ages. A prolific writer and former president of the Tennessee Academy of Science, she has received recognition at the state, national, and international levels and was a part of the writing team to put together an Environmental Literacy Plan for Students in Tennessee. She can be contacted at [email protected]. Jeff D. Thomas earned his EdD at Columbia University, Teachers College in New York City. Dr. Thomas is an Assistant Professor of Science and Science Education in the Department of Physics and Earth Science at Central Connecticut State University. He teaches earth and physical science courses as well as methods courses for pre- and in-service K-12 science educators. His research interests include curriculum development, geoscience education, inquiry-oriented instruction, and the nature of science. Dr. Thomas has publications in Science Scope and The Science Teacher. Dr. Thomas was also the principal investigator for a federally-funded Teacher Quality Partnership Grant, titled Interdisciplinary Science, Inquiry and Literacy Institute. Craig A. Wilson earned his PhD in curriculum and instruction from the University of Toledo. Dr. Wilson is a professor of education in the Early Childhood and Elementary Education Department at East Stroudsburg University in Pennsylvania, where he teaches undergraduate and graduate science methods courses and a graduate research course. His primary research interests are in field-based

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experiences, inquiry-oriented instruction, and technology integration. He has been published in the Middle School Journal, Science Scope, Pennsylvania Teacher Educator, and Best Products in Mathematics and Science, a monograph from the Collaborative for Excellence in Teacher Preparation in Pennsylvania. He was the project leader for a grant program at East Stroudsburg University, entitled Middle School Science Certification for Special Education Preservice Teachers. Supported by the Pennsylvania Department of Education, this project brought four science professors and three education professors together to work on a highly collaborative program. He can be contacted at [email protected].

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