Campbell Biology: Concepts & Connections, 7th Edition

Brief Contents 1

Biology: Exploring Life 1

UNIT V

Animals: Form and Function

UNIT I

The Life of the Cell 2

The Chemical Basis of Life 16

3

The Molecules of Cells

4

A Tour of the Cell 50

5

The Working Cell 72

6

How Cells Harvest Chemical Energy

7

Photosynthesis: Using Light to Make Food 106

32

88

UNIT II

Cellular Reproduction and Genetics 8

The Cellular Basis of Reproduction and Inheritance

9

Patterns of Inheritance

152

10

Molecular Biology of the Gene 180

11

How Genes Are Controlled 208

12

DNA Technology and Genomics

14

The Origin of Species

15

Tracing Evolutionary History

21

Nutrition and Digestion 428

22

Gas Exchange 452

23

Circulation 466

24

The Immune System

25

Control of Body Temperature and Water Balance

26

Hormones and the Endocrine System

27

Reproduction and Embryonic Development

28

Nervous Systems 562

29

The Senses 586

30

How Animals Move 602

484

516 532

Plants: Form and Function 230

Concepts of Evolution How Populations Evolve 254

Unifying Concepts of Animal Structure and Function 412

UNIT VI

UNIT III

13

124

20

31

Plant Structure, Growth, and Reproduction 620

32

Plant Nutrition and Transport 642

33

Control Systems in Plants 660

UNIT VII

276

Ecology 292

UNIT IV

The Evolution of Biological Diversity 16

Microbial Life: Prokaryotes and Protists

318

17

The Evolution of Plant and Fungal Diversity

18

The Evolution of Invertebrate Diversity

19

The Evolution of Vertebrate Diversity

364 388

340

34

The Biosphere: An Introduction to Earth's Diverse Environments 678

35

Behavioral Adaptations to the Environment 698

36

Population Ecology

37

Communities and Ecosystems 738

38

Conservation Biology

722

760

504

CAMPBELL

BIOLOGY C O N C E P T S

&

C O N N E C T I O N S

JANE B. REECE Berkeley, California MARTHA R.TAYLOR Cornell University ERIC J. SIMON New England College JEAN L. DICKEY Clemson University

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Cover Photo Credits: Ring-tailed lemur (Lemur catta) looking down from large spiney plant, Itampolo, South Madagascar; Inaki Relanzon / Nature Picture Library (front cover) Frank Krahmer / Photolibrary (back cover)

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Copyright ©2012, 2009, 2006 Pearson Education, Inc., publishing as Pearson Benjamin Cummings, 1301 Sansome Street, San Francisco, CA 94111. All rights reserved. Manufactured in the United States of America. This publication is protected by Copyright and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. To obtain permission(s) to use material from this work, please submit a written request to Pearson Education, Inc., Permissions Department, 1900 E. Lake Ave., Glenview, IL 60025. For information regarding permissions, call (847) 486-2635. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed in initial caps or all caps. Pearson Benjamin Cummings™ is a trademark, in the U.S. and/or other countries, of Pearson Education, Inc., or its affiliates. Library of Congress Cataloging-in-Publication Data Campbell biology : concepts & connections / Jane B. Reece . . . [et al.]. p. cm. Revised ed. of: Biology : concepts & connections / Neil A. Campbell, et al. c2009. Includes index. ISBN 0-321-69681-6 (hardcover) 1. Biology. I. Reece, Jane B. II. Biology. QH308.2.B56448 2012 570—dc22 2011000193 ISBN 10: 0-321-69681-6; ISBN 13: 978-0-321-69681-6 (Student edition) ISBN 10: 0-321-70923-3; ISBN 13: 978-0-321-70923-3 (Exam copy) ISBN 10: 0-321-74203-6; ISBN 13: 978-0-321-74203-2 (Books a la Carte edition) 1 2 3 4 5 6 7 8 9 10—CRK—15 14 13 12 11 www.pearsonhighered.com

About the Authors Jane B. Reece has worked in biology publishing since 1978, when she joined the editorial staff of Benjamin Cummings. Her education includes an A.B. in biology from Harvard University (where she was initially a philosophy major), an M.S. in microbiology from Rutgers University, and a Ph.D. in bacteriology from the University of California, Berkeley. At UC Berkeley and later as a postdoctoral fellow in genetics at Stanford University, her research focused on genetic recombination in bacteria. Dr. Reece taught biology at Middlesex County College (New Jersey) and Queensborough Community College (New York). During her 12 years as an editor at Benjamin Cummings, she played a major role in a number of successful textbooks. She is lead author of Campbell Biology, Ninth Edition, and coauthor of Campbell Essential Biology, Fourth Edition, and Campbell Essential Biology with Physiology, Third Edition.

Martha R. Taylor has been teaching biology for more than 35 years. She earned her B.A. in biology from Gettysburg College and her M.S. and Ph.D. in science education from Cornell University. She was assistant director of the Office of Instructional Support at Cornell for 7 years. Dr. Taylor has taught introductory biology for both majors and nonmajors at Cornell University and is currently a lecturer in the Learning Strategies Center teaching supplemental biology courses. Her experience working with students in classrooms, in laboratories, and with tutorials has increased her commitment to helping students create their own knowledge of and appreciation for biology. She has been the author of the Student Study Guide for all nine editions of Campbell Biology. Eric J. Simon is an associate professor in the Department of Biology and Health Science at New England College, in Henniker, New Hampshire. He teaches introductory biology to science majors and nonscience majors, as well as upper-level courses in genetics, microbiology, tropical marine biology, and molecular biology.

Dr. Simon received a B.A. in biology and computer science and an M.A. in biology from Wesleyan University and a Ph.D. in biochemistry from Harvard University. His research focuses on innovative ways to use technology to improve teaching and learning in the science classroom, particularly for nonscience majors. Dr. Simon is the lead author of Campbell Essential Biology, Fourth Edition, and Campbell Essential Biology with Physiology, Third Edition.

Jean L. Dickey is a professor of biology at Clemson University. She had no idea that science was interesting until her senior year in high school, when a scheduling problem landed her in an advanced biology course. Abandoning plans to study English or foreign languages, she enrolled in Kent State University as a biology major. After receiving her B.S. in biology, she went on to earn a Ph.D. in ecology and evolution from Purdue University. Since joining the faculty at Clemson in 1984, Dr. Dickey has specialized in teaching nonscience majors, including a course designed for preservice elementary teachers and workshops for in-service teachers. She also developed an investigative laboratory curriculum for general biology. Dr. Dickey is author of Laboratory Investigations for Biology, Second Edition, and coauthor of Campbell Essential Biology, Fourth Edition, and Campbell Essential Biology with Physiology, Third Edition. Neil A. Campbell (1946–2004) combined the inquiring nature of a research scientist with the soul of a caring teacher. Over his 30 years of teaching introductory biology to both science majors and nonscience majors, many thousands of students had the opportunity to learn from him and be stimulated by his enthusiasm for the study of life. While he is greatly missed by his many friends in the biology community, his coauthors remain inspired by his visionary dedication to education and are committed to searching for ever better ways to engage students in the wonders of biology.

About the Authors

iii

To the Student: How to use this book C H A P T E R

The Cellular Basis of Reproduction and Inheritance

8

Introduce yourself to the chapter. See where you are headed.

BIG IDEAS

Look for the Big Ideas, which open each chapter and provide a transit map to a set of overarching concepts.

FPO

Remember the big picture.

Cell Division and Reproduction

Look for the main headings that organize the chapter around the big ideas.

(8.1–8.2)

Cell division underlies many of life's important processes.

The Eukaryotic Cell Cycle and Mitosis (8.3–8.10)

Cells produce genetic duplicates through an ordered, tightly controlled series of steps.

Cell Division and Reproduction

Colorized TEM 5,000⫻

8.1 Cell division plays many important roles in the lives of organisms The ability of organisms to reproduce their own kind is the one characteristic that best distinguishes living things from nonliving matter (see Module 1.1 to review the characteristics of life). Only amoebas produce more amoebas, only people make more people, and only maple trees produce more maple trees. These simple facts of life have been recognized for thousands of years and are summarized by the age-old saying, “Like begets like.” However, the biological concept of reproduction includes more than just the birth of new organisms: Reproduction actually occurs much more often at the cellular level. When a cell undergoes reproduction, or cell division, the two “daughter” cells that result are genetically identical to each other and to the original “parent” cell. (Biologists traditionally use the word daughter in this context; it does not imply gender.) Before the parent cell splits into two, it duplicates its chromosomes, the structures that contain most of the cell’s DNA. Then, during the division process, one set of chromosomes is distributed to each daughter cell. As a rule, the daughter cells receive identical sets of chromosomes from the lone, original parent cell. Each offspring cell will thus be genetically identical to the other and to the original parent cell. Sometimes, cell division results in the reproduction of a whole organism. Many single-celled organisms, such as prokaryotes or the eukaryotic yeast cell in Figure 8.1A, reproduce by dividing in half, and the offspring are genetic replicas. This is an example of asexual reproduction, the creation of genetically identical offspring by a single parent, without the participation  Figure 8.1A of sperm and A yeast cell producing egg. Many a genetically identical multicellular daughter cell by asexual reproduction organisms can

reproduce asexually as well. For example, some sea star species have the ability to grow new individuals from fragmented pieces (Figure 8.1B). And if you’ve ever grown a houseplant from a clipping, you’ve observed  Figure 8.1B A sea star asexual reproduction in plants reproducing asexually (Figure 8.1C). In asexual reproduction, there is one simple principle of inheritance: The lone parent and each of its offspring have identical genes. Sexual reproduction is different; it requires fertilization of an egg by a sperm. The production of gametes—egg and sperm—involves a special type of cell division that occurs only in reproductive organs (such as testes and ovaries in humans). As you’ll learn later in the chapter, a gamete has only half as many chromosomes as the parent cell that gave rise to it, and these chromosomes contain unique combinations of genes. Therefore, in sexually reproducing species, like does not precisely beget like (Figure 8.1D). Offspring produced by sexual reproduction generally resemble their parents more closely than they resemble unrelated individuals of the same species, but they are not identical to their  Figure 8.1C An African parents or to each other. Each violet reproducing asexually offspring inherits a unique from a cutting (the large leaf combination of genes from its two on the left)  Figure 8.1D Sexual reproduction produces offspring with unique combinations of genes

Meiosis and Crossing Over (8.11–8.17)

The process of meiosis produces genetically varied haploid gametes from diploid cells.

Alterations of Chromosome Number and Structure (8.18–8.23)

Errors in cell division can produce organisms with abnormal numbers of chromosomes. 124

Focus on what’s important. Use both text and figures as you study.

The figures illuminate the text and vice versa. Text and figures are always together— so you’ll never have to turn a page to find what you need. 126

Understand biology one concept at a time.

Each module features a central concept, announced in its heading.

iv

To the Student: How to use this book

FPO he photo above shows a cancer cell undergoing cell division, the creation of two cells from one. Cancer cells start as normal body cells that, because of genetic mutations, lose the ability to control the tempo of their own division. The result is rapid cell division that is no longer under the control of the host body—cell growth run amok! If left untreated, cancer cells may continue to divide and spread, invading other tissues and eventually killing the host. Most cancer treatments seek to prevent this outcome by disrupting one or more steps in cell division. Some anticancer drugs target dividing DNA; others disrupt cellular structures that assist in cell division. The goal of cancer treatment is to slow the spread of cancerous cells to the point that the body’s immune system can overtake the growth, destroying the abnormal cells and restoring proper control of cell division.

T

Although cell division is harmful when it happens in a cancer cell, it is a necessary process for all forms of life. Why must cells divide? Some organisms, such as single-celled prokaryotes, reproduce themselves by splitting a single parent cell via cell division, creating two genetically identical offspring. In your body and the bodies of all other multicellular organisms, cell division allows for growth, replacement of damaged cells, and development of an embryo into an adult. Furthermore, in sexually reproducing organisms, eggs and sperm result from a particular type of cell division. These examples illustrate the main point of this chapter: The perpetuation of life, including all aspects of reproduction and inheritance, is based on the reproduction of cells, or cell division. In this chapter, we discuss the two main types of cell division— mitosis and meiosis—and how they function within organisms.

Discover.

The opening essays introduce the chapter topic through stories that will pique your curiosity.

125

10.20 The AIDS virus makes DNA on an RNA template

?

Why is HIV classified as a retrovirus?

Viral RNA

Never get lost.

Figures describing a process take you through a series of numbered steps keyed to explanations in the text.

resulting viral DNA enters the cell’s nucleus and inserts itself into the chromosomal DNA, becoming a provirus (analogous to a prophage). The host’s RNA polymerase ��� transcribes the proviral DNA into RNA, which can then be ��� translated by ribosomes into viral proteins. ��� New viruses assembled from these components leave the cell and can infect other cells. HIV infects and kills white blood cells that play important roles in the body’s immune system. The loss of such cells causes the body to become susceptible to other infections that it would normally be able to fight off. Such secondary infections cause the syndrome (a collection of symptoms) that can kill an AIDS patient. We discuss AIDS in more detail when we take up the immune system in Chapter 24.

● It synthesizes DNA from its RNA genome. This is the reverse (“retro”) of the usual DNA : RNA information flow.

The devastating disease AIDS (acquired immunodeficiency syndrome) is caused by HIV (human immunodeficiency virus), an RNA virus with some special properties. In outward appearance, HIV resembles the flu or mumps virus (Figure 10.20A). Its membranous envelope and glycoprotein spikes enable HIV to enter and leave a host cell much the way the mumps virus does (see Figure 10.18). Notice, however, that HIV contains two identical copies of its RNA instead of one. HIV also has a different mode of replication. HIV carries molecules of an enzyme called reverse transcriptase, which catalyzes reverse transcription, the synthesis of DNA on an RNA template. This unusual process which is opposite the usual DNA : RNA flow of genetic information, characterizes retroviruses (retro means “backward”). Figure 10.20B illustrates what happens after HIV RNA is uncoated in the cytoplasm of a host cell. ��� Reverse transcriptase ( ) uses the RNA as a template to make a DNA strand and then ��� adds a second, complementary DNA strand. ��� The

Envelope

DNA strand

Glycoprotein Protein coat RNA (two identical strands) Reverse transcriptase (two copies)

 Figure 10.20A A model of HIV structure

Reverse transcriptase

���

Get immediate feedback with a checkpoint question at the end of each module.

Chromosomal DNA

���

Doublestranded DNA Viral RNA and proteins

CYTOPLASM NUCLEUS

Test yourself.

��� ���

Provirus DNA

��� RNA

���

 Figure 10.20B The behavior of HIV nucleic acid in a host cell

To the Student: How to use this book

v

To the Student: How to use this book (continued) Learn about biology in your world.

Make a connection.

19.17 Our knowledge of animal diversity is far from complete

CONNECTION

Connection modules relate biology to your life and interests.

When an Englishman sent home the skin of a duck-billed platypus more than 200 years ago, it was one of thousands of previously unknown species of organisms pouring into Europe from naturalists exploring Africa, Asia, and North and South Americ Ame rica, ric a,, as wel welll as as Australia. Aust ust America, You might think that after centturies turi tur uries ies off scientific sci scien ientifi tific ific exploration, exp expl xpl pllo orr only tiny organisms such as microbes and insects remain reemai to be found. But the days of Connection Module topicsexploring include: new ecosys stem and discovering new species are not ecosystems over. In fact, better ac cces to remote areas, coupled with new access mapping technologie es, h technologies, has renewed the pace of discovery. AcModule 5.16 – Many drugs, cording to a report issued isssue in 2009, 18,516 species were depesticides, and poisons are scribed for the first time tiime in 2007. As you might expect from Module 18.12, over half half of them were insects, but the list also enzyme inhibitors includes more than 1, ,200 vertebrates. 1,200 regio on of o Southeast Asia, an area of diverse The Mekong region Module 16.16 – Can algae provide landscapes surrounding surroundiing the Mekong River as it flows from a renewable energy source? southern China to th he C the China Sea, is one of many treasure troves of previously u nkn unknown species that are currently being explored. paast d decade, more than 1,000 new species Module 17.13 – Plant diversity is Over vitalthe past have been identified in in the th region, including the leopard gecko to the future of the world's food in Figuresupply 19.17A, onee o off more than 400 new species of vertebrates that scientists h have av turned up there. To the southeast, reModule 32.9 – Soil conversation he iisland of New Guinea are also yielding mote mountains on tthe hundreds of discoveries, discoverries, including a frog with a droopy nose is essential to human life (Figure 19.17B) and tthe he tiny wallaby shown in Figure 19.17C. off m monkey found in more than a century The first new species o Module 37.23 – Ecosystem services was discovered in thee eeastern as Himalayas. Discoveries of new extremely rare, but four others have also primate species are ex xtre xt are essential to human well-being been made recently: ttwo wo new lemur species in Madagascar and two new new m monk onkeys onk eys y , aan nO monkeys, Old World species in Tanzania and a New Wo New W orld ld sp ecies eci iess in in B Bo o World species Bolivia. Previously undescribed species are being reported almost daily from every continent and a wide variety of habitats. And researchers are just beginning to explore the spectacular

FPO

diversity of the oceans. The Census of Marine Life, a decadelong collaboration among scientists from 80 nations, has reported the discovery of more than 5,000 new species. Thousands more are expected to be found as new technology enables scientists to investigate deep-sea habitats. Recent expeditions have also gleaned hundreds of new species from the seas surrounding Antarctica, and the collapse of Antarctic ice shelves has allowed researchers their first glimpse of life on a seafloor that had previously been hidden from view. Even places that are regularly visited by people offer surprises. For example, over 100 new marine species were identified recently on a coral reef near Australia. When a new species is described, taxonomists learn as much as possible about its physical and genetic characteristics and assign it to the appropriate groups in the Linnaean system. As a result, most new species automatically acquire a series of names from domain through genus. But every species also has a unique identifier, and the honor of choosing it belongs to the discoverer. Species are often named for their habitat or a notable feature. In a new twist, naming rights for recently discovered species have been auctioned off to raise money for conservation organizations, which undertake many of the projects that survey biological diversity. The right to name a new species of monkey cost the winning bidder $650,000, and donors spent more than $2 million for the honor of naming 10 new species of fish. Naming rights are available for smaller budgets, too—the top bid to name a new species of shrimp was $2,900. The proceeds from these auctions go toward funding new expeditions and preserving the habitats of the newly discovered species. In many cases, such discoveries are made as roads and settlements reach farther into new territory. Consequently, many species are endangered soon after they are discovered. We’ll consider the various threats to biological diversity in Chapter 38.

?

What factors are responsible for the recent increase in the number of new species found? ● Technology; encroachment of human activities into wilderness areas

 Figure 19.17A Leopard gecko, a newly discovered lizard from northern Vietnam

 Figure 19.17B Pinocchio frog, recently discovered in New Guinea

408

CHAPTER 19

The Evolution of Vertebrate Diversity

A narrative written with you in mind.

This best-selling text has undergone an extensive revision to make biology even more approachable with increased use of analogies, real world examples, and more conversational language. vi

To the Student: How to use this book

 Figure 19.17C Dwarf wallaby, a rabbitsized member of the kangaroo family

Discover how science works. Scientific Discovery modules demonstrate the process of science, research, and discovery.

10.19 Emerging viruses threaten human health

Viruses that appear suddenly or are new to medical scientists are called emerging viruses. There are many familiar examples. HIV, the AIDS virus, is a classic example: This virus appeared in New York and California in the early 1980s, seemingly out of nowhere. The deadly Ebola virus, recognized initially in 1976 in central Africa, is one of several emerging viruses that cause hemorrhagic fever, an often fatal illness characterized by fever, vomiting, massive bleeding, and circulatory system collapse. A number of other dangerous new viruses cause encephalitis, an inflammation of the brain. One example is the West Nile virus, which appeared for the first time in North America in 1999 and has since spread to all 48 contiguous U.S. states. West Nile virus is spread primarily by mosquitoes, which carry the virus in blood sucked from one victim and can transfer it to another victim. Severe acute respiratory syndrome (SARS) first appeared in China in 2002. Within eight months, about 8,000 people were infected, of whom some 10% died. Researchers quickly identified the infectious agent as a previously unknown, single-stranded RNA coronavirus, so named for its crown-like “corona” of spikes. From where and how do such viruses burst on the human scene, giving rise to rare or previously unknown diseases? Three processes contribute to the emergence of viral diseases: t ti t tb t i d df i l td

SCIENTIFIC DISCOVERY

Colorized TEM 8,500⫻

Evolution Connection modules in every chapter relate evolution to a wide spectrum of biology topics and help explain the mechanisms underlying evolution and the evidence for it.

EVOLUTION CONNECTION

 Figure 10.19 People in Mexico City wearing masks in an attempt to prevent spread of the 2009 H1N1 virus (shown in the inset)

H1N1 (Figure 10.19). This particular virus evolved through

5.7 Research on another membrane protein led to the

discovery of aquaporins Peter Agre received the 2003 Nobel Prize in Chemistry for his discovery of aquaporins. In a recent interview, Dr. Agre described his research that led to this discovery: I’m a blood specialist (hematologist), and my particular interest has been proteins found in the plasma membrane of red blood cells. When I joined the faculty at the John Hopkins School of Medicine, I began to study the Rh blood antigens. Rh is of medical importance because of Rh incompatibility, which occurs when Rh-negative mothers have Rh-positive babies. Membrane-spanning proteins are really messy to work with. But we worked out a method to isolate the Rh protein. Our sample seemed to consist of two proteins, but we were sure that the smaller one was just a breakdown product of the larger one. We were completely wrong. Using antibodies we made to the smaller protein, we showed it to be one of the most abundant proteins in red cell membranes—200,000 copies per cell!—and even more abundant in certain kidney cells.

said this couldn’t be enough, especially for cells whose water permeability needs to be very high or regulated. For example, our kidneys must filter and reabsorb many liters of water every day. . . . People whose kidney cells have defective aquaporin molecules need to drink 20 liters of water a day to prevent dehydration. In addition, some patients make too much aquaporin, causing them to retain too much fluid. Fluid retention in pregnant women is caused by the synthesis of too much aquaporin. Knowledge of aquaporins may in the future contribute to the solution of medical problems.

We asked Dr. Agre why cells have aquaporins. Not all cells do. Before our discovery, however, many physiologists thought that diffusion was enough for getting water into and out of all cells. Others

Figure 5.7 is an image taken from a simulation produced by computational biophysicists at the University of Illinois, Urbana. Their model included four aquaporin channels spanning a membrane. You can see a line of blue water molecules flipping their way single file through the gold aquaporin. The simulation of this flipping movement allowed researchers to discover how aquaporins selectively allow only water molecules to pass through them.

?  Figure 5.7 Aquaporin in action

Why are aquaporins important in kidney cells? ● Kidney cells must reabsorb a large amount of water when producing urine.

Learn about the mechanisms underlying evolution.

To the Student: How to use this book

vii

To the Student: How to use this book (continued) Feel confident going into the test.

C H A P T E R

1 0

R E V I E W

For Practice Quizzes, BioFlix, MP3 Tutors, and Activities, go to www.masteringbiology.com.

10.10

Reviewing the Concepts

Transfer RNA molecules serve as interpreters during translation. Translation takes place in the cytoplasm. A ribosome at-

10.11

The Structure of the Genetic Material (10.1–10.3) 10.1 Experiments showed that DNA is the genetic material. One key experiment demonstrated that certain phages (bacterial viruses) reprogram host cells to produce more phages by injecting their DNA.

DNA and RNA are polymers of nucleotide.

10.2

A

T

G

C

Sugarphosphate backbone

A

T

A C

Phosphate group

G T

C

C

T

A

DNA

C

10.14

Sugar

RNA C G A U

Sugar

Deoxyribose

Ribose

A

DNA

Polynucleotide

Growing polypeptide

DNA replication depends on specific base pairing. DNA

replication starts with the separation of DNA strands. Enzymes then use each strand as a template to assemble new nucleotides into a complementary strand. 10.5 DNA replication proceeds in two directions at many sites simultaneously. Using the enzyme DNA polymerase, the cell

synthesizes one daughter strand as a continuous piece. The other strand is synthesized as a series of short pieces, which are then connected by the enzyme DNA ligase.

The Flow of Genetic Information from DNA to RNA to Protein (10.6–10.16) 10.6

The DNA genotype is expressed as proteins, which provide

the molecular basis for phenotypic traits. The DNA of a gene—a linear sequence of many nucleotides—is transcribed into RNA, which is translated into a polypeptide. 10.7 Genetic information written in codons is translated into amino acid sequences. Codons are base triplets. 10.8 The genetic code dictates how codons are translated into amino acids. Nearly all organisms use an identical genetic code to

convert the codons of a gene to the amino acid sequence of a polypeptide.

Anticodon

Codons

Small ribosomal subunit

10.15 Review: The flow of genetic information in the cell is DNA : RNA : protein. The sequence of codons in DNA, via the

sequence of codons in mRNA, spells out the primary structure of a polypeptide. 10.16 Mutations can change the meaning of genes. s. Mutations d by errors in are changes in the DNA nucleotide sequence, caused DNA replication or recombination, or by mutagens.. Substituting, 10.21 Viroids and prions are formidable pathogens in plants and inserting, or deleting nucleotides alters a gene, with varying effects animals. Viroids are RNA molecules that can infect plants. Prions on the organism. are infectious proteins that can cause brain diseases in animals. The Genetics of Viruses and Bacteria (10.17–10.23) 10 0.23) 10.22 Bacteria can transfer DNA in three ways. Bacteria can 10.17 Viral DNA may become part of the host chromosome. omosome. transfer genes from cell to cell by transformation, transduction, or Viruses can be regarded as genes packaged in protein. in. When conjugation. phage DNA enters a lytic cycle inside a bacterium, it is replicated, transcribed, and translated; the new viral DNA and protein mol- 10.23 Bacterial plasmids can serve as carriers for gene transfer. ecules then assemble into new phages, which burst from the host Plasmids are small circular DNA molecules separate from the cell. In the lysogenic cycle, phage DNA inserts into the host chro-bacterial chromosome. er cells. Much mosome and is passed on to generations of daughter later, it may initiate phage production. Connecting the Concepts 10.18 Many viruses cause disease in animals and plants. Flu 1. Check your understanding of the flow of genetic information an DNA, as viruses and most plant viruses have RNA, rather than through a cell by filling in the blanks. their genetic material. Some animal viruses steal a bit of host cell is a polymer an remain lamembrane as a protective envelope. Some viruses can (a) made from DNA tent in the host’s body for long periods. monomers called

Transcription produces genetic messages in the form of RNA. In the nucleus, the DNA helix unzips, and RNA nucleotides

10.19

Emerging viruses threaten human health.

10.20

The AIDS virus makes DNA on an RNA template. plate. HIV is a

line up and hydrogen-bond along one strand of the DNA, following the base-pairing rules.

NA, which then retrovirus: It uses RNA as a template for making DNA, inserts into a host chromosome. (b)

10.9

206

tRNA

mRNA

DNA is a double-stranded helix. Watson and Crick worked out the three-dimensional structure of DNA: two polynucleotide strands wrapped around each other in a double helix. Hydrogen bonds between bases hold the strands together. Each base pairs with a complementary partner: A with T, G with C.

DNA Replication (10.4–10.5)

Amino acid

Large ribosomal subunit

10.3

10.4

The Reviewing the Concepts section provides helpful summary diagrams and references back to the text.

codon at a time relative to the ribosome, a tRNA with a complementary anticodon pairs with each codon, adding its amino acid to the growing polypeptide chain.

C G A T

G

Review the main points.

An initiation codon marks the start of an mRNA message.

Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation. As the mRNA moves one

DNA

G T

G

Nitrogenous bases

T

A G T A

T

10.13

C

G

taches to the mRNA and translates its message into a specific polypeptide, aided by transfer RNAs (tRNAs). Each tRNA is a folded molecule bearing a base triplet called an anticodon on one end; a specific amino acid is added to the other end. 10.12 Ribosomes build polypeptides. Made of rRNA and proteins, ribsomes have binding sites for tRNAs and mRNA.

Nitrogenous base

Nucleotide

A G

Eukaryotic RNA is processed before leaving the nucleus as

mRNA. Noncoding segments of RNA called introns are spliced out, and a cap and tail are added to the ends of the mRNA.

CHAPTER 10

is performed by an enzyme called

Prepare for the test.

Use the questions that appear in the Testing Your Knowledge section to prepare for your upcoming tests. viii

To the Student: How to use this book

Describing, Comparing, and Explaining

7. Describe the process by which the information in a eukaryotic gene is transcribed and translated into a protein. Correctly use these words in your description: tRNA, amino acid, start codon, transcription, RNA splicing, exons, introns, mRNA, gene, codon, RNA polymerase, ribosome, translation, anticodon, peptide bond, stop codon.

(c)

(d)

RNA

Connecting the Concepts activities test your ability to link topics from different modules and include concept mapping, labeling, and categorizing exercises.

5. The nucleotide sequence of a DNA codon is GTA. A messenger RNA molecule with a complementary codon is transcribed from the DNA. In the process of protein synthesis, a transfer RNA pairs with the mRNA codon. What is the nucleotide sequence of the tRNA anticodon? a. CAT d. CAU b. CUT e. GT c. GUA

6. Describe the process of DNA replication: the ingredients needed, the steps in the process, and the final product.

Molecular Biology of the Gene

Connect the chapter’s key concepts.

4. Which of the following correctly ranks the structures in order of size, from largest to smallest? a. gene-chromosome-nucleotide-codon b. chromosome-gene-codon-nucleotide c. nucleotide-chromosome-gene-codon d. chromosome-nucleotide-gene-codon e. gene-chromosome-codon-nucleotide

comes in three kinds called

(e)

Applying the Concepts

(f) molecules are components of

(g) is performed by structures called

use amino-acid-bearing molecules called

(h)

Protein

one or more polymers made from monomers called

(i)

Testing Your Knowledge Multiple Choice 2. Scientists have discovered how to put together a bacteriophage with the protein coat of phage T2 and the DNA of phage lambda. If this composite phage were allowed to infect a bacterium, the phages produced in the host cell would have ____________. (Explain your answer.) a. the protein of T2 and the DNA of lambda b. the protein of lambda and the DNA of T2 c. a mixture of the DNA and proteins of both phages d. the protein and DNA of T2 e. the protein and DNA of lambda 3. A geneticist found that a particular mutation had no effect on the polypeptide encoded by a gene. This mutation probably involved a. deletion of one nucleotide. b. alteration of the start codon. c. insertion of one nucleotide. d. deletion of the entire gene. e. substitution of one nucleotide.

8. A cell containing a single chromosome is placed in a medium containing radioactive phosphate so that any new DNA strands formed by DNA replication will be radioactive. The cell replicates its DNA and divides. Then the daughter cells (still in the radioactive medium) replicate their DNA and divide, and a total of four cells are present. Sketch the DNA molecules in all four cells, showing a normal (nonradioactive) DNA strand as a solid line and a radioactive DNA strand as a dashed line. 9. The base sequence of the gene coding for a short polypeptide is CTACGCTAGGCGATTGACT. What would be the base sequence of the mRNA transcribed from this gene? Using the genetic code in Figure 10.8A, give the amino acid sequence of the polypeptide translated from this mRNA. (Hint: What is the start codon?) 10. Researchers on the Human Genome Project have determined the nucleotide sequences of human genes and in many cases identified the proteins encoded by the genes. Knowledge of the nucleotide sequences of genes might be used to develop lifesaving medicines or treatments for genetic defects. In the United States, both government agencies and biotechnology companies have applied for patents on their discoveries of genes. In Britain, the courts have ruled that a naturally occurring gene cannot be patented. Do you think individuals and companies should be able to patent genes and gene products? Before answering, consider the following: What are the purposes of a patent? How might the discoverer of a gene benefit from a patent? How might the public benefit? What might be some positive and negative results of patenting genes? Answers to all questions can be found in Appendix 4.

Chapter 10 Review

207

MasteringBiology®: Study tools Study tools that you can access from anywhere. www.masteringbiology.com Highlight Function Lets you highlight what you want to remember.

Interactive Glossary I t ti Gl Provides pop-up definitions and terms.

Annotation Function Allows you to take notes.

Google®-based search function.

Zoom Lets you zoom in and out for better viewing.

Hyperlinks Links to quizzes, tests, activities, and animations.

I t t N Instructor Notes t Your instructor might also share his or her notes and highlights with the class.

Access highly interactive activities with 3-D animations.

BioFlix® activities help you to visualize and learn the toughest topics in biology.

BioFlix Activity

BioFlix Animation MasteringBiology®: Study Tools

ix

MasteringBiology ®: Assignments created by the authors Over 200 new MasteringBiology activities written by the author team help you arrive prepared for lectures and provide you with feedback and coaching.

www.masteringbiology.com

Arrive prepared for lecture. 䉳

Video Tutor Sessions and MP3 Tutor Sessions

Co-author Eric Simon hosts these on-the-go tutorials focused on key concepts and vocabulary.

Video Tutor Session

䉳 Building Vocabulary Activities Practice the new vocabulary you are learning in class.

Connect the art to the concepts you are learning and enhance the text’s visual approach to learning biology.

x

MasteringBiology®: Assignments created by the authors

䉳

Learning Through Art Activities

䉳 Connecting the

Concepts Activities

Link the concepts you learned and see how they work together.

Explore the data behind hot topics so you can make informed decisions.

䉳

You Decide Activities

Plus, Interpreting Data Activities offer coaching on how to read and interpret data and graphs.

MasteringBiology®: Assignments created by the authors

xi

MasteringBiology®: To the Instructor MasteringBiology is an online assessment and tutorial system designed to help instructors teach more efficiently and is pedagogically proven to help students learn. It helps instructors maximize class time with customizable, easy-to-assign, and automatically graded assessments that motivate students to learn outside of class and arrive prepared for lecture.

www.masteringbiology.com

Access students results with easy-to-interpret insights into student performance.

䉳 Gradebook

Get easy-to-interpret insights into student performance using the Gradebook. • Every assignment is automatically graded. • At a glance, shades of red highlight vulnerable students and challenging assignments.

Student Performance Data

䉳

Wrong answer summaries

䉳

reveals how students are doing compared to a national average and which topics they’re struggling with.

give unique insight into your students’ misconceptions and support just-in-time teaching.

xii

MasteringBiology®: To the Instructor

See at a glance where students are struggling and gain insight into their progress. 䉳

Get daily diagnostics.

Gradebook Diagnostics provide unique insight into class and student performance. With a single click, charts summarize the most difficult problems, vulnerable students, grade distribution, and even score improvement over the duration of the course.

MasteringBiology® is easy for you and your students to use. 䉳 The Mastering platform

is the most effective and widely-used online tutorial, homework, and assessment system for the sciences. • Developed by scientists for science students and instructors • Over one million active registrations • Data-supported efficacy • A proven history with over 9 years of student use • Active users in all 50 states and in 30 countries • 99.8% server reliability

With MasteringBiology, you can: • Assign publisher-created pre-built assignments to get started quickly. • Easily edit any of our questions or answers to match the precise language you use. • Import your own questions and begin compiling meaningful data on student performance. • Easily export grades to Microsoft®Excel or other course management systems. • Compare your current class performance to that of previous classes and to the system average. • Communicate with your students through announcements, email, and document posting.

Efficacy Studies

Go to the “Proven Results” tab at www.masteringbiology.com to see efficacy studies.

MasteringBiology®: To the Instructor

xiii

Preface

I

nspired by the thousands of students in our own classes over the years and enthusiastic feedback from the many instructors who have used our book, we are delighted to present this new, Seventh Edition. We authors have worked together closely to ensure that both the book and the supplementary material online reflect the evolving needs of today’s courses and students, as well as current progress in biology. Now titled Campbell Biology: Concepts & Connections to honor Neil Campbell’s founding role and his many contributions to biology education, this book has always had a dual purpose: to engage students from a wide variety of majors in the wonders of the living world and to show them how biology relates to their own existence and the world they inhabit. Most of these students will not become biologists themselves, but their lives will be touched by biology every day. Today, understanding the concepts of biology and their connections to our lives is more important than ever. Whether we’re concerned with our own health or the health of our planet, a familiarity with biology is essential. This basic knowledge and an appreciation for how science works have become elements of good citizenship in an era when informed evaluations of health issues, environmental problems, and applications of new technology are critical.

Concepts and Connections Concepts Biology is a vast subject that gets bigger every year, but an introductory biology course is still only one or two terms long. This book was the first introductory biology textbook to use concept modules to help students recognize and focus on the main ideas of each chapter. The heading of each module is a carefully crafted statement of a key concept. For example, “Two photosystems connected by an electron transport chain generate ATP and NADPH” announces a key concept about the light reactions of photosynthesis (Module 7.8). Such a concept heading serves as a focal point, and the module’s text and illustrations converge on that concept with explanation and, often, analogies. The module text walks the student through the illustrations, just as an instructor might do in class. And in teaching a sequential process, such as the one diagrammed in Figure 7.8A, we number the steps in the text to correspond to numbered steps in the figure. The synergy between a module’s verbal and graphic components transforms the concept heading into an idea with meaning to the student. The checkpoint question at the end of each module encourages students to test themselves as they proceed through a chapter. Finally, in the Chapter Review, all the concept statements are listed under the overarching section titles, explicitly reminding students of what they’ve just studied. Connections

Students are more motivated to study biology when they can connect it to their own lives and interests—for example, to health issues, economic problems, environmental xiv

Preface

quality, ethical controversies, and social responsibility. In this edition, blue Connection tabs mark the numerous application modules that go beyond the core biological concepts. Other connections are made in the chapter-opening essays and throughout the text. Moreover, we connect the content of each chapter to the grand unifying theme of evolution, without which the study of life has no coherence. This book remains the only non-majors biology text to connect every single chapter to evolution, with highlights featured in greentabbed Evolution Connection modules.

New to This Edition New Big Ideas and Chapter Transit Maps

In this Seventh Edition, we take our conceptual emphasis to the next level, reframing each chapter with a smaller set of overarching concepts—“Big Ideas”—that are introduced at the beginning of the chapter. Each big idea corresponds to a major section of the chapter, and they are tied together in a “transit map” that shows the route by which the student will proceed through the chapter.

More Engaging Narrative and a New Look With the goal of making the concepts of biology more accessible and increasing the overall friendliness of the book, every chapter in this edition makes greater use of analogies, intriguing facts, examples that relate topics to the student and the real world, engaging questions, and a more conversational tone. The fresh new design used for the pages and the redesign of many figures make the book more accessible. See pages 280–281 for an example. New Scientific Discovery Modules

This edition gives greater emphasis to “how we know what we know” through a new type of module, called Scientific Discovery and marked with an orange tab. For example, the new Module 16.11 introduces Koch’s postulates for identifying the cause of an infectious disease and relates how Australian microbiologist Barry Marshall used these criteria to demonstrate that most peptic ulcers are caused by a particular bacterium (a discovery that won him a Nobel Prize). Along with new Scientific Discovery modules created for this edition, we have recast Talking About Science modules and some other material from the last edition in the Scientific Discovery format to help make research advances more vivid to students. The improved introduction to the process of science in Chapter 1 will equip students to appreciate the many examples throughout the book of how scientific concepts emerge from observations and experimental evidence.

The Latest Science Biology is a dynamic field of study, and we have always taken pride in our book’s currency and scientific accuracy. For this edition, as always, we have integrated the results of the latest scientific research throughout the book. We have done this with careful thought, recognizing

that research advances can lead to new ways of looking at biological topics; such changes in perspective can necessitate organizational changes in our textbook to better reflect the current state of a field. You will find a unit-by-unit account of new content and organizational improvements in the “New Content” section on pp. xvi–xvii, following this Preface.

New MasteringBiology® A specially developed version of MasteringBiology, the most widely used online tutorial and assessment program for biology, is now included with Campbell Biology: Concepts & Connections. The book’s authors have created over 200 new Mastering activities to help students understand core concepts. An average of five author-created activities per chapter help students learn vocabulary, extend the book’s emphasis on visual learning, demonstrate the connections among key concepts (helping students grasp the big ideas), and coach students on how to interpret data. Included online are 18 BioFlix® 3-D animations of difficult topics (with accompanying tutorials), new Video Tutor Sessions, MP3 Tutor Sessions, Discovery Channel™ Videos, and YouDecide and GraphIt! activities.

This Book’s Flexibility Though a biology textbook’s table of contents must be linear, biology itself is more like a web of related concepts without a single starting point or prescribed path. Courses can navigate this network starting with molecules, with ecology, or somewhere in between, and most courses omit some topics. Campbell Biology: Concepts & Connections is uniquely suited

to serve this variety of courses. The seven units of the book are largely self-contained, and in a number of the units, chapters can be assigned in a different order without much loss of coherence. The use of numbered modules makes it easy to omit modules or to relocate modules within a syllabus. ■ ■ ■

For many students, introductory biology is the only science course that they will take during their college years. Long after today’s students have forgotten most of the specific content of their biology course, they will be left with general impressions and attitudes about science and scientists. We hope that this new edition of Campbell Biology: Concepts & Connections helps make those impressions positive and supports instructors’ goals for sharing the fun of biology. In our continuing efforts to improve the book and its supporting materials, we benefit tremendously from instructor feedback, not only in formal reviews but also via informal communication. Please let us know how we are doing and how we can improve the next edition of the book. Jane Reece, [email protected] Martha Taylor (Units I and III, and Chapters 1 and 20–23), [email protected] Eric Simon (Units II and VI, and Chapters 24–29), [email protected] Jean Dickey (Units IV and VII, and Chapter 30), [email protected]

Preface

xv

New Content

B

elow are a few highlights of new content and organizational improvements in Campbell Biology: Concepts & Connection, Seventh Edition.

Chapter 1, Biology: Exploring Life

The ring-tailed lemur, our cover subject for the Seventh Edition, is featured in the chapter opener and comes up again in the modules on the hierarchy of life, the interactions of organisms with their environments, and the scientific method. (Lemurs also appear in later chapters.) The opening modules of Chapter 1 have been reorganized to emphasize the common properties of living organisms and the themes that help organize the study of biology. The modules on the scientific method have been reframed to more accurately reflect the scientific process, with a focus on observations and hypotheses and a new section on the culture of science.

principles. A new art style helps students follow a genetic cross through multiple generations, while the text discussions linked to the figures have been revised to be both clearer and more accessible. This content is then reinforced with updated discussions of relevant topics, such as cystic fibrosis, achondroplasia, and the effect of the environment on sex determination in some species. This edition includes discussion of many recent advances in the field. Some concern our basic understanding of genetics, introducing students to some of the latest discoveries in epigenetics, microRNAs, and other mechanisms by which cells control gene expression. Other new material discusses applications, such as the 2009 epidemic of H1N1 flu, recent gene therapy trials, new applications of genetic engineering to agriculture and human health, and advances in stem cell research.

Unit III, Concepts of Evolution Our main goal in revising Unit I, The Life of the Cell Throughout the first unit of chapters, the structure and functions of DNA have received increased coverage, as a basic understanding of nucleic acids has become more relevant to the general public. As we developed our new transit map feature, we carefully analyzed the organization of each chapter and then moved, combined, and even split some modules to improve the conceptual flow within each chapter. New subheads have been added to several modules to help students see at a glance how the material is organized. Preexisting Connection modules have been updated with new information. A new Connection module, “Many drugs, pesticides, and poisons are enzyme inhibitors,” has been added to Chapter 5, and a Connection module in Chapter 6, “Interrupting cellular respiration can have both harmful and helpful effects,” has been expanded. These Connection modules provide real-world examples relating to important metabolic processes. A beautiful and instructive new illustration has been added to Module 5.1 to show the various functions of membrane proteins. The illustration of phospholipids has been moved from Chapter 4 to the section on lipids in Chapter 3 so that students can more easily compare the structures of fats, fatty acids, and phospholipids (see Modules 3.8 and 3.9). The new Scientific Discovery module in Chapter 7, Module 7.14, highlights the scientists whose work contributed to the recognition and explanation of ozone depletion in the atmosphere and draws parallels with the current controversy around global climate change.

Unit II, Cellular Reproduction and Genetics The purpose of this unit is to help students understand the relationship between DNA, chromosomes, and organisms and to help them see that genetics is not purely hypothetical but connects in many important and interesting ways to their lives, human society, and other life on Earth. In preparing this edition, we worked to clarify difficult concepts, enhancing text and illustrations and providing timely new applications of genetic xvi

New Content

this edition was to provide a coherent storyline that presents the basic principles of evolution and natural selection, the mountains of evidence that support these theories, and their relevance to all of biology—and to the lives of students. We have strengthened the conceptual organization of the unit, ensuring that the chapters and modules flow smoothly to build a clear picture of what evolution is and how it works. The particularly important Chapter 14, “The Origin of Species,” includes a number of improvements. Module 14.3, the two-page introduction to reproductive barriers, has a new diagram and more effective photos. Within Module 14.4, on allopatric speciation, a new section presents evidence of this type of speciation using new research on sister species of snapping shrimp separated by the Isthmus of Panama. Module 14.8, a heavily revised module on adaptive radiation on isolated islands, now faces a Scientific Discovery module featuring the long-term research of Peter and Rosemary Grant on Galápagos Island finches.

Unit IV, The Evolution of Biological Diversity The diversity unit surveys all life on Earth in less than a hundred pages! Consequently, descriptions and illustrations of the unifying characteristics of each major group of organisms, along with a small sample of its diversity, make up the bulk of the content. Two recurring elements are interwoven with these descriptions: evolutionary history and examples of relevance to our everyday lives and society at large. For the Seventh Edition, we have improved and updated those two elements. For instance, the evolution thread has been strengthened by changes in Chapter 16 that emphasize the evolutionary relationships between protists and multicellular eukaryotes. A new Evolution Connection in Chapter 18, Module 18.16, describes recent research on the role of homeotic genes in generating animal diversity. New Connection modules in this unit cover relevant topics such as biofilms (Module 16.5), algae as a renewable energy source (Module 16.16), the

importance of plant diversity to the future of the world’s food supply (Module 17.13), and exciting discoveries of new animal species (Module 19.17). In addition, Chapter 16 has been substantially reorganized to make it flow more logically, to strengthen connections among topics, and to make the terminology more manageable. The entire unit has been updated. For example, the human evolution section of Chapter 19 describes the recently reported hominin Ardipithecus ramidus and its significance to the evolution of our own species.

Unit V, Animals: Form and Function

This unit combines a comparative approach with an exploration of human anatomy and physiology. Most chapters begin with an overview of a general problem that animals face and a comparative discussion of how different animals address this problem, within an evolutionary context. The main part of every chapter is devoted to more detailed presentations of human body systems, frequently illuminated by discussion of the health consequences of disorders in those systems. Improvements in this edition include new descriptions and illustrations that help clarify important but difficult concepts— for example, innate versus adaptive immunity (Modules 24.1–24.15), clonal selection (Module 24.7), hormonal control of osmoregulation (Module 25.9), and the maintenance of resting potential in neurons (Module 28.3). Updates of health applications in Connection and other modules include the latest efforts to develop an AIDS vaccine (Module 24.13), advances in our understanding of autoimmune diseases (Module 24.16), sex hormone abuse by professional athletes (Module 26.10), and HPV vaccination (Module 27.7). In addition, the chapter on nutrition and digestion, Chapter 21, has an increased focus on obesity, including the chapteropening essay and updated information on healthy eating.

Unit VI, Plants: Form and Function

To help students gain an appreciation of the importance of plants, this unit presents

the anatomy and physiology of angiosperms with frequent connections to the importance of plants to society. New connections in this edition include the link between overextraction of groundwater for irrigation and the appearance of sinkholes (Module 32.9), while plant growth is related to the grafting of grapevines for wine production (Module 31.14). Throughout the unit, the text has been revised with the goal of making the material more engaging and accessible to students. There are new discussions of the Dust Bowl of the 1930s (Module 32.9), organic farming (and the multiple meanings of “organic”) as one means of achieving sustainable agriculture (Module 32.10), and the challenge of feeding the world’s human population (Module 32.11). These modules make the point that human society is inexorably connected to the health of plants.

Unit VII, Ecology In this unit, students learn the fundamental principles of ecology and how these principles apply to environmental problems. For the Seventh Edition, the ecology unit has been extensively revised, with the goal of updating content to reflect current issues and research wherever possible. For example, the Deepwater Horizon oil spill is mentioned in several places, including the opening essay for Chapter 37. Global climate change is featured throughout the unit as a major ecological challenge for this generation. In addition to the four modules in Chapter 38 on climate change, the consequences of climate change are discussed elsewhere as well. New Connection modules focus on the degradation of aquatic ecosystems (Module 37.22); the necessity of ecosystem services for human well-being (Module 37.23); and the threats to biodiversity from habitat destruction, invasive species, overharvesting, and pollution (Module 38.2). Many core concept modules also include examples of current issues—for instance, plastic microbeads, deforestation in Haiti, acid rain from recent nitrogen pollution, blackfooted ferrets, and ecotourism.

New Content

xvii

Acknowledgments

T

his Seventh Edition of Campbell Biology: Concepts & Connections is a result of the combined efforts of many talented and hardworking people, and the authors wish to extend heartfelt thanks to all those who contributed to this and previous editions. Our work on this edition was shaped by input from the biologists acknowledged in the Seventh Edition reviewer list on pages xix–xxi, who shared with us their experiences teaching introductory biology and provided specific suggestions for improving the book. Feedback from the authors of this edition’s supplements and the unsolicited comments and suggestions we received from many biologists and biology students were also extremely helpful. In addition, this book has benefited in countless ways from the stimulating contacts we have had with the coauthors of Campbell Biology, Ninth Edition. We wish to offer special thanks to the students and faculty at our teaching institutions. Marty Taylor thanks her students at Cornell University for their valuable feedback on the book. Eric Simon thanks his colleagues and friends at New England College, especially within the collegium of Natural Sciences and Mathematics, for their continued support and assistance. And Jean Dickey thanks her colleagues at Clemson University for their expertise and support. The superb publishing team for this edition was headed up again by executive editor Chalon Bridges, with the invaluable support of editor-in-chief Beth Wilbur. We cannot thank them enough for their unstinting efforts on behalf of the book and for their commitment to excellence in biology education. We are fortunate to have had once again the contributions of executive director of development Deborah Gale and senior editorial manager Ginnie Simione Jutson. Ginnie coordinated the project on a daily basis, miraculously maintaining a calm—and calming—demeanor while solving thorny problems and soothing frayed nerves. We are similarly grateful to the members of the editorial development team—Evelyn Dahlgren, Kim Krummel, Mary Ann Murray, Debbie Hardin, and John Burner—for their steadfast commitment to quality. We thank them for their thoroughness and hard work; the book is far better than it would have been without their efforts. Thanks also to senior supplements project editor Susan Berge for her oversight of the supplements program and to editorial assistant Rachel Brickner for the efficient and enthusiastic support she provided for the entire project. We wish to express our appreciation to Linda Davis, president of Pearson Math and Science, Paul Corey, president of Pearson Benjamin Cummings, and Michael Young, editorial director, for their ongoing support. This book and all the other components of the teaching package are both attractive and pedagogically effective in large part because of the hard work and creativity of the production professionals on our team. We wish to thank managing editor Mike Early, production project manager Lori Newman, and

xviii

Acknowledgments

executive managing editor Erin Gregg. We are happy to thank copyeditor Janet Greenblatt, proofreaders Joanna Dinsmore and Pete Shanks, and indexer Lynn Armstrong. We again thank senior photo editor Donna Kalal and photo researcher Kristin Piljay for their contributions, as well as permissions editors Sue Ewing and Beth Keister. Electronic Publishing Services, Inc. was in charge of composition and rendering of new and revised illustrations. Finally, we thank manufacturing buyer Michael Penne. Users of the Seventh Edition will enjoy the book’s new look. We thank Gary Hespenheide for creating a beautiful and functional interior design, and we are again indebted to design manager Marilyn Perry. For yet another striking cover, we thank our old friend Yvo Riezebos. The value of Campbell Biology: Concepts & Connections as a learning tool is greatly enhanced by the hard work and creativity of the authors of the supplements that accompany this book: Ed Zalisko (Instructor’s Guide and PowerPoint® Lecture Presentations); Richard Liebaert (Student Study Guide); Kelly Hogan (Active Learning Ideas); Jennifer Yeh (Test Bank, Reading Quizzes and Media Correlations); Cindy Klevickis (Study Area Practice Tests); and Shannon Datwyler (Study Card, Clicker Questions, and Quiz Shows). In addition to Susan Berge, the editorial and production staff for the supplements program included Kim Wimpsett of Happenstance Type-ORama, Brady Golden, Jane Brundage, James Bruce, and John Hammett. And the superlative MasteringBiology® program for this book would not exist without Lauren Fogel, Stacy Treco, Natania Mlawer, Jonathan Ballard, Katie Foley, Kristen Sutton, Sarah Jensen, Beth Winickoff, Juliana Tringali, Sean O’Connor, Caroline Power, and David Kokorowski and his team. Thank you, one and all! For their important roles in marketing the book, we are very grateful to marketing manager Lauren Garritson, executive marketing manager Lauren Harp, and director of marketing Christy Lawrence. We also appreciate the work of MasteringBiology® marketers Brian Buckley and Scott Dustan and the marketing communications team—Lillian Carr, Jane Campbell, Jessica Perry, and Jessica Tree. The members of the Pearson Science sales team have continued to help us connect with biology instructors and their teaching needs. We thank them for all their hard work and enthusiastic support. Finally, we are deeply grateful to our families and friends for their support, encouragement, and patience throughout this project. Our special thanks to: Paul, Dan, Maria, Armelle, and Sean (J.B.R.); Josie, Jason, Marnie, Alice, Jack, David, Paul, and Ava (M.R.T.); Amanda, Reed, Forest, and dear friends Jamey, Nick, Jim, and Bethany (E.J.S.); and Jessie and Katherine (J.L.D.). Jane Reece, Martha Taylor, Eric Simon, and Jean Dickey

Reviewers Reviewers of the Seventh Edition Caroline Ballard, Rock Valley College Lisa K. Bonneau, Metropolitan Community College, Blue River Delia Brownson, University of Texas at Austin and Austin Community College John Campbell, Northern Oklahoma College Jocelyn Cash, Central Piedmont Community College Mitch Cruzan, Portland State University Pat Davis, East Central Community College Jean DeSaix, University of North Carolina at Chapel Hill Mary Dettman, Seminole State College of Florida Douglas Gayou, University of Missouri at Columbia Julie Gibbs, College of DuPage Eileen Gregory, Rollins College Sig Harden, Troy University Montgomery Brenda Hunzinger, Lake Land College Mark E. Jackson, Central Connecticut State University Robert Johnson, Pierce College, Lakewood Campus John C. Jones, Calhoun Community College Cindy Klevickis, James Madison University Kurt Dubear Kroening, University of Wisconsin, Fox Valley Margaret Maile Lam, Kapiolani Community College MaryLynne LaMantia, Golden West College Dale Lambert, Tarrant County College, Northeast Liz Lawrence, Miles Community College William Lemon, Southwestern Oregon Community College Laurie M. Len, El Camino College Caroline McNutt, Schoolcraft College Jamie Moon, University of North Florida Kathryn Nette, Cuyamaca College James Newcomb, New England College Zia Nisani, Antelope Valley College Phillip Pack, Woodbury University Jack Plaggemeyer, Little Big Horn College Elena Pravosudova, University of Nevada, Reno Kimberly Puvalowski, Old Bridge High School Shanmugavel Rajendran, Baltimore City Community College Luis A. Rodriguez, San Antonio Colleges Connie Rye, East Mississippi Community College John Richard Schrock, Emporia State University Sam C. Sochet, Thomas Edison Career and Technical Education High School Linda Brooke Stabler, University of Central Oklahoma Megan Stringer, Jones County Junior College John Tolli, Southwestern College Mike Tveten, Pima College Rani Vajravelu, University of Central Florida Sarah VanVickle-Chavez, Washington University Frederick W. Vogt, Elgin Community College Dennis Walsh, MassBay Community College Lisa Weasel, Portland State University Jennifer Wiatrowski, Pasco-Hernando Community College

Robert R. Wise, University of Wisconsin Oshkosh Mary E. Wisgirda, San Jacinto College Tumen Wuliji, College of Agriculture, Biotechnology and Natural Resources at University of Nevada, Reno Martin Zahn, Thomas Nelson Community College

Reviewers of Previous Editions Michael Abbott, Westminster College Tanveer Abidi, Kean University Daryl Adams, Mankato State University Dawn Adrian Adams, Baylor University Olushola Adeyeye, Duquesne University Shylaja Akkaraju, Bronx Community College Felix Akojie, Paducah Community College Dan Alex, Chabot College John Aliff, Georgia Perimeter College Sylvester Allred, Northern Arizona University Jane Aloi-Horlings, Saddleback College Loren Ammerman, University of Texas at Arlington Dennis Anderson, Oklahoma City Community College Marjay Anderson, Howard University Bert Atsma, Union County College Yael Avissar, Rhode Island College Gail Baker, LaGuardia Community College Andrei Barkovskii, Georgia College and State University Mark Barnby, Ohlone College Chris Barnhart, University of San Diego Stephen Barnhart, Santa Rosa Junior College William Barstow, University of Georgia Kirk A. Bartholomew, Central Connecticut State University Michael Battaglia, Greenville Technical College Gail Baughman, Mira Costa College Jane Beiswenger, University of Wyoming Tania Beliz, College of San Mateo Lisa Bellows, North Central Texas College Ernest Benfield, Virginia Polytechnic Institute Rudi Berkelhamer, University of California, Irvine Harry Bernheim, Tufts University Richard Bliss, Yuba College Lawrence Blumer, Morehouse College Dennis Bogyo, Valdosta State University Mehdi Borhan, Johnson County Community College Kathleen Bossy, Bryant College William Bowen, University of Arkansas at Little Rock Robert Boyd, Auburn University Bradford Boyer, State University of New York, Suffolk County Community College Paul Boyer, University of Wisconsin William Bradshaw, Brigham Young University Agnello Braganza, Chabot College James Bray, Blackburn College Peggy Brickman, University of Georgia Chris Brinegar, San Jose State University Chad Brommer, Emory University Charles Brown, Santa Rosa Junior College Carole Browne, Wake Forest University

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xix

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xx

Reviewers

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Reviewers

xxi

Detailed Contents 1

Biology: Exploring Life

2.6

1

2.7

Themes in the Study of Biology 2 1.1 1.2

1.3 1.4

2.8

All forms of life share common properties 2 In life’s hierarchy of organization, new properties emerge at each level 3 Cells are the structural and functional units of life 4 Organisms interact with their environment, exchanging matter and energy

2.9

Water’s Life-Supporting Properties 26 2.10 2.11 2.12

5

1.6 1.7

2.13 2.14

Evolution, the Core Theme of Biology 6 1.5

Covalent bonds join atoms into molecules through electron sharing 22 Ionic bonds are attractions between ions of opposite charge 24 Hydrogen bonds are weak bonds important in the chemistry of life 24 Chemical reactions make and break chemical bonds 25

The unity of life is based on DNA and a common genetic code 6 The diversity of life can be arranged into three domains 6 Evolution explains the unity and diversity of life 8

2.15 2.16

Hydrogen bonds make liquid water cohesive 26 Water’s hydrogen bonds moderate temperature 26 Ice is less dense than liquid water 27 Water is the solvent of life 27 The chemistry of life is sensitive to acidic and basic conditions 28 Connection Acid precipitation and ocean acidification threaten the environment 29 Evolution Connection The search for extraterrestrial life centers on the search for water 29

Chapter Review 30

The Process of Science 9 1.8 1.9

Scientific inquiry is used to ask and answer questions about nature 9 Scientists form and test hypotheses and share their results 10

Biology and Everyday Life 1.10 1.11

12 Connection Biology, technology, and society are connected in important ways 12 Evolution Connection Evolution is connected to our everyday lives 12

Chapter Review 13

3

Introduction to Organic Compounds 34 3.1 3.2 3.3

3.4 3.5

The Life of the Cell

3.6

The Chemical Basis of Life

16

Elements, Atoms, and Compounds 18 2.1 2.2 2.3 2.4

Organisms are composed of elements, in combinations called compounds 18 Connection Trace elements are common additives to food and water 19 Atoms consist of protons, neutrons, and electrons 20 Connection Radioactive isotopes can help or harm us 21

3.7

xxii

The distribution of electrons determines an atom’s chemical properties 22

Contents

Life’s molecular diversity is based on the properties of carbon 34 A few chemical groups are key to the functioning of biological molecules 35 Cells make a huge number of large molecules from a limited set of small molecules 36 37 Monosaccharides are the simplest carbohydrates 37 Two monosaccharides are linked to form a disaccharide 38 Connection What is high-fructose corn syrup, and is it to blame for obesity? 38 Polysaccharides are long chains of sugar units 39

Lipids 40 3.8 3.9

3.10

Fats are lipids that are mostly energy-storage molecules 40 Phospholipids and steroids are important lipids with a variety of functions 41 Connection Anabolic steroids pose health risks 41

Proteins 42 3.11

Chemical Bonds 22 2.5

32

Carbohydrates

UNIT I

2

The Molecules of Cells

3.12

Proteins are made from amino acids linked by peptide bonds 42 A protein’s specific shape determines its function 43

3.13

A protein’s shape depends on four levels of structure 44

4.20

Nucleic Acids

4.21

3.14

4.22

3.15 3.16

46 DNA and RNA are the two types of nucleic acids 46 Nucleic acids are polymers of nucleotides 46 Evolution Connection Lactose tolerance is a recent event in human evolution 47

Chapter Review 48

4

A Tour of the Cell

50

Introduction to the Cell 52 4.1 4.2

4.3 4.4

Microscopes reveal the world of the cell 52 The small size of cells relates to the need to exchange materials across the plasma membrane 54 Prokaryotic cells are structurally simpler than eukaryotic cells 55 Eukaryotic cells are partitioned into functional compartments 56

The Nucleus and Ribosomes 58 4.5 4.6

The nucleus is the cell’s genetic control center 58 Ribosomes make proteins for use in the cell and for export 59

The Endomembrane System 59 4.7 4.8 4.9 4.10 4.11 4.12

Overview: Many cell organelles are connected through the endomembrane system 59 The endoplasmic reticulum is a biosynthetic factory 60 The Golgi apparatus finishes, sorts, and ships cell products 61 Lysosomes are digestive compartments within a cell 62 Vacuoles function in the general maintenance of the cell 62 A review of the structures involved in manufacturing and breakdown 63

Chapter Review 70

5

4.14 4.15

Mitochondria harvest chemical energy from food 63 Chloroplasts convert solar energy to chemical energy 64 Evolution Connection Mitochondria and chloroplasts evolved by endosymbiosis 64

The Working Cell

72

Membrane Structure and Function 74 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9

Membranes are fluid mosaics of lipids and proteins with many functions 74 Evolution Connection Membranes form spontaneously, a critical step in the origin of life 75 Passive transport is diffusion across a membrane with no energy investment 75 Osmosis is the diffusion of water across a membrane 76 Water balance between cells and their surroundings is crucial to organisms 76 Transport proteins can facilitate diffusion across membranes 77 Scientific Discovery Research on another membrane protein led to the discovery of aquaporins 78 Cells expend energy in the active transport of a solute 78 Exocytosis and endocytosis transport large molecules across membranes 79

Energy and the Cell 5.10 5.11 5.12

80 Cells transform energy as they perform work 80 Chemical reactions either release or store energy 81 ATP drives cellular work by coupling exergonic and endergonic reactions 82

How Enzymes Function 83 5.13 5.14 5.15 5.16

Energy-Converting Organelles 63 4.13

Three types of cell junctions are found in animal tissues 68 Cell walls enclose and support plant cells 68 Review: Eukaryotic cell structures can be grouped on the basis of four main functions 69

Enzymes speed up the cell’s chemical reactions by lowering energy barriers 83 A specific enzyme catalyzes each cellular reaction 84 Enzyme inhibitors can regulate enzyme activity in a cell 85 Connection Many drugs, pesticides, and poisons are enzyme inhibitors 85

Chapter Review 86

6

How Cells Harvest Chemical Energy 88

The Cytoskeleton and Cell Surfaces 65 4.16 4.17 4.18 4.19

The cell’s internal skeleton helps organize its structure and activities 65 Cilia and flagella move when microtubules bend 66 Connection Problems with sperm motility may be environmental or genetic 67 The extracellular matrix of animal cells functions in support and regulation 67

Cellular Respiration: Aerobic Harvesting of Energy 90 6.1

6.2 6.3

Photosynthesis and cellular respiration provide energy for life 90 Breathing supplies O2 for use in cellular respiration and removes CO2 90 Cellular respiration banks energy in ATP molecules 91 Contents

xxiii

6.4

Connection The human body uses energy from ATP

6.5

for all its activities 91 Cells tap energy from electrons “falling” from organic fuels to oxygen 92

7.9

The Calvin Cycle: Reducing CO2 to Sugar 7.10

Stages of Cellular Respiration 93 6.6 6.7 6.8 6.9

6.10 6.11 6.12

Overview: Cellular respiration occurs in three main stages 93 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate 94 Pyruvate is oxidized prior to the citric acid cycle 96 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 molecules 96 Most ATP production occurs by oxidative phosphorylation 98 Connection Interrupting cellular respiration can have both harmful and beneficial effects 99 Review: Each molecule of glucose yields many molecules of ATP 100

7.11

6.14

Fermentation enables cells to produce ATP without oxygen 100 Evolution Connection Glycolysis evolved early in the history of life on Earth 102

7.12 7.13 7.14

6.16

Cells use many kinds of organic molecules as fuel for cellular respiration 102 Food molecules provide raw materials for biosynthesis 103

UNIT II

Cellular Reproduction and Genetics

8 8.1

8.2

Photosynthesis: Using Light to Make Food 106

An Overview of Photosynthesis 108

7.2 7.3

7.4 7.5

Autotrophs are the producers of the biosphere 108 Photosynthesis occurs in chloroplasts in plant cells 109 Scientific Discovery Scientists traced the process of photosynthesis using isotopes 110 Photosynthesis is a redox process, as is cellular respiration 110 Overview: The two stages of photosynthesis are linked by ATP and NADPH 111

The Light Reactions: Converting Solar Energy to Chemical Energy 112 7.6 7.7 7.8

xxiv

Visible radiation absorbed by pigments drives the light reactions 112 Photosystems capture solar energy 113 Two photosystems connected by an electron transport chain generate ATP and NADPH 114

Contents

Cell division plays many important roles in the lives of organisms 126 Prokaryotes reproduce by binary fission 127

The Eukaryotic Cell Cycle and Mitosis 128 8.3

7.1

The Cellular Basis of Reproduction and Inheritance 124

Cell Division and Reproduction 126

Chapter Review 104

7

Review: Photosynthesis uses light energy, carbon dioxide, and water to make organic molecules 118 Connection Photosynthesis may moderate global climate change 119 Scientific Discovery Scientific study of Earth’s ozone layer has global significance 120

Chapter Review 121

Connections Between Metabolic Pathways 102 6.15

116 ATP and NADPH power sugar synthesis in the Calvin cycle 116 Evolution Connection Other methods of carbon fixation have evolved in hot, dry climates 117

Photosynthesis Reviewed and Extended 118

Fermentation: Anaerobic Harvesting of Energy 100 6.13

Chemiosmosis powers ATP synthesis in the light reactions 115

8.4 8.5 8.6 8.7 8.8 8.9 8.10

The large, complex chromosomes of eukaryotes duplicate with each cell division 128 The cell cycle multiplies cells 129 Cell division is a continuum of dynamic changes 130 Cytokinesis differs for plant and animal cells 132 Anchorage, cell density, and chemical growth factors affect cell division 133 Growth factors signal the cell cycle control system 134 Connection Growing out of control, cancer cells produce malignant tumors 135 Review: Mitosis provides for growth, cell replacement, and asexual reproduction 136

Meiosis and Crossing Over 136 8.11 8.12 8.13

Chromosomes are matched in homologous pairs 136 Gametes have a single set of chromosomes 137 Meiosis reduces the chromosome number from diploid to haploid 138

8.14 8.15

8.16 8.17

Mitosis and meiosis have important similarities and differences 140 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring 141 Homologous chromosomes may carry different versions of genes 142 Crossing over further increases genetic variability 142

Alterations of Chromosome Number and Structure 144 8.18 8.19 8.20 8.21 8.22 8.23

A karyotype is a photographic inventory of an individual’s chromosomes 144 Connection An extra copy of chromosome 21 causes Down syndrome 145 Accidents during meiosis can alter chromosome number 146 Connection Abnormal numbers of sex chromosomes do not usually affect survival 146 Evolution Connection New species can arise from errors in cell division 147 Connection Alterations of chromosome structure can cause birth defects and cancer 148

9.15

The environment affects many characters 170

The Chromosomal Basis of Inheritance 170 9.16 9.17 9.18 9.19

Chromosome behavior accounts for Mendel’s laws 170 Scientific Discovery Genes on the same chromosome tend to be inherited together 172 Scientific Discovery Crossing over produces new combinations of alleles 172 Geneticists use crossover data to map genes 174

Sex Chromosomes and Sex-Linked Genes 9.20 9.21 9.22 9.23

174 Chromosomes determine sex in many species 174 Sex-linked genes exhibit a unique pattern of inheritance 176 Connection Human sex-linked disorders affect mostly males 177 Evolution Connection The Y chromosome provides clues about human male evolution 177

Chapter Review 178

10 Molecular Biology of the Gene

180

Chapter Review 149

9

The Structure of the Genetic Material 182

Patterns of Inheritance

152

Mendel’s Laws 9.1 9.2

9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10

154 The science of genetics has ancient roots 154 Experimental genetics began in an abbey garden 154 Mendel’s law of segregation describes the inheritance of a single character 156 Homologous chromosomes bear the alleles for each character 157 The law of independent assortment is revealed by tracking two characters at once 158 Geneticists can use the testcross to determine unknown genotypes 159 Mendel’s laws reflect the rules of probability 160 Connection Genetic traits in humans can be tracked through family pedigrees 161 Connection Many inherited disorders in humans are controlled by a single gene 162 Connection New technologies can provide insight into one’s genetic legacy 164

10.1 10.2 10.3

DNA Replication 10.4 10.5

10.6 10.7 10.8 10.9 10.10

10.11 10.12

9.11

10.13

9.12 9.13 9.14

188 DNA replication depends on specific base pairing 188 DNA replication proceeds in two directions at many sites simultaneously 188

The Flow of Genetic Information from DNA to RNA to Protein 190

Variations on Mendel’s Laws

166 Incomplete dominance results in intermediate phenotypes 166 Many genes have more than two alleles in the population 167 A single gene may affect many phenotypic characters 168 A single character may be influenced by many genes 169

Scientific Discovery Experiments showed that DNA is the genetic material 182 DNA and RNA are polymers of nucleotides 184 Scientific Discovery DNA is a double-stranded helix 186

10.14

10.15 10.16

The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits 190 Genetic information written in codons is translated into amino acid sequences 191 The genetic code dictates how codons are translated into amino acids 192 Transcription produces genetic messages in the form of RNA 193 Eukaryotic RNA is processed before leaving the nucleus as mRNA 194 Transfer RNA molecules serve as interpreters during translation 194 Ribosomes build polypeptides 196 An initiation codon marks the start of an mRNA message 196 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation 197 Review: The flow of genetic information in the cell is DNA → RNA → protein 198 Mutations can change the meaning of genes 199 Contents

xxv

The Genetics of Viruses and Bacteria 200 10.17 10.18 10.19 10.20 10.21 10.22 10.23

11.15 Connection Therapeutic cloning can produce stem cells

Viral DNA may become part of the host chromosome 200 Connection Many viruses cause disease in animals and plants 201 Evolution Connection Emerging viruses threaten human health 202 The AIDS virus makes DNA on an RNA template 203 Viroids and prions are formidable pathogens in plants and animals 203 Bacteria can transfer DNA in three ways 204 Bacterial plasmids can serve as carriers for gene transfer 205

Chapter Review 206

11 How Genes Are Controlled

11.2

11.3 11.4 11.5 11.6 11.7 11.8 11.9 11.10

11.11

11.12 11.13 11.14

xxvi

221 Plant cloning shows that differentiated cells may retain all of their genetic potential 221 Nuclear transplantation can be used to clone animals 222 Connection Reproductive cloning has valuable applications, but human reproductive cloning raises ethical issues 222

Contents

11.16 11.17 11.18 11.19

Cancer results from mutations in genes that control cell division 224 Multiple genetic changes underlie the development of cancer 225 Faulty proteins can interfere with normal signal transduction pathways 226 Connection Lifestyle choices can reduce the risk of cancer 227

Chapter Review 228

and Genomics

208

Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes 210 Chromosome structure and chemical modifications can affect gene expression 212 Complex assemblies of proteins control eukaryotic transcription 214 Eukaryotic RNA may be spliced in more than one way 214 Small RNAs play multiple roles in controlling gene expression 215 Later stages of gene expression are also subject to regulation 216 Review: Multiple mechanisms regulate gene expression in eukaryotes 217 Cell signaling and cascades of gene expression direct animal development 218 Connection DNA microarrays test for the transcription of many genes at once 219 Signal transduction pathways convert messages received at the cell surface to responses within the cell 220 Evolution Connection Cell-signaling systems appeared early in the evolution of life 220

Cloning of Plants and Animals

The Genetic Basis of Cancer 224

12 DNA Technology

Control of Gene Expression 210 11.1

with great medical potential 223

230

Gene Cloning 232 12.1 12.2 12.3 12.4 12.5

Genes can be cloned in recombinant plasmids 232 Enzymes are used to “cut and paste” DNA 234 Cloned genes can be stored in genomic libraries 235 Reverse transcriptase can help make genes for cloning 235 Nucleic acid probes identify clones carrying specific genes 236

Genetically Modified Organisms 236 12.6 12.7 12.8 12.9 12.10

Recombinant cells and organisms can mass-produce gene products 236 Connection DNA technology has changed the pharmaceutical industry and medicine 238 Connection Genetically modified organisms are transforming agriculture 239 Genetically modified organisms raise concerns about human and environmental health 240 Connection Gene therapy may someday help treat a variety of diseases 241

DNA Profiling 242 12.11

12.12 12.13 12.14 12.15 12.16

The analysis of genetic markers can produce a DNA profile 242 The PCR method is used to amplify DNA sequences 242 Gel electrophoresis sorts DNA molecules by size 243 STR analysis is commonly used for DNA profiling 244 Connection DNA profiling has provided evidence in many forensic investigations 245 RFLPs can be used to detect differences in DNA sequences 246

Genomics 247 12.17

Genomics is the scientific study of whole genomes 247

12.18 Connection The Human Genome Project revealed

12.19 12.20 12.21

that most of the human genome does not consist of genes 248 The whole-genome shotgun method of sequencing a genome can provide a wealth of data quickly 249 Proteomics is the scientific study of the full set of proteins encoded by a genome 249 Evolution Connection Genomes hold clues to human evolution 250

13.17

Chapter Review 274

14 The Origin of Species 14.1 14.2 14.3

Concepts of Evolution

13 How Populations Evolve

254

14.4 14.5 14.6

13.2

13.3 13.4 13.5 13.6

A sea voyage helped Darwin frame his theory of evolution 256 Darwin proposed natural selection as the mechanism of evolution 258 Scientists can observe natural selection in action 259 The study of fossils provides strong evidence for evolution 260 Many types of scientific evidence support the evolutionary view of life 262 Homologies indicate patterns of descent that can be shown on an evolutionary tree 263

The Evolution of Populations 264 13.7 13.8 13.9 13.10

Evolution occurs within populations 264 Mutation and sexual reproduction produce the genetic variation that makes evolution possible 264 The Hardy-Weinberg equation can test whether a population is evolving 266 Connection The Hardy-Weinberg equation is useful in public health science 267

Mechanisms of Microevolution 268 13.11 13.12 13.13 13.14 13.15 13.16

Natural selection, genetic drift, and gene flow can cause microevolution 268 Natural selection is the only mechanism that consistently leads to adaptive evolution 269 Natural selection can alter variation in a population in three ways 270 Sexual selection may lead to phenotypic differences between males and females 271 Evolution Connection The evolution of antibiotic resistance in bacteria is a serious public health concern 272 Diploidy and balancing selection preserve genetic variation 272

The origin of species is the source of biological diversity 278 There are several ways to define a species 278 Reproductive barriers keep species separate 280

Mechanisms of Speciation 282

Darwin’s Theory of Evolution 256 13.1

276

Defining Species 278

Chapter Review 250 UNIT III

Natural selection cannot fashion perfect organisms 273

14.7 14.8 14.9 14.10 14.11

In allopatric speciation, geographic isolation leads to speciation 282 Reproductive barriers can evolve as populations diverge 283 Sympatric speciation takes place without geographic isolation 284 Evolution Connection Most plant species trace their origin to polyploid speciation 285 Isolated islands are often showcases of speciation 286 Scientific Discovery A long-term field study documents evolution in Darwin’s finches 287 Hybrid zones provide opportunities to study reproductive isolation 288 Speciation can occur rapidly or slowly 289

Chapter Review 290

15 Tracing Evolutionary History

292

Early Earth and the Origin of Life 15.1 15.2

15.3

294 Conditions on early Earth made the origin of life possible 294 Scientific Discovery Experiments show that the abiotic synthesis of organic molecules is possible 295 Stages in the origin of the first cells probably included the formation of polymers, protocells, and selfreplicating RNA 296

Major Events in the History of Life 297 15.4

15.5 15.6

The origins of single-celled and multicelled organisms and the colonization of land were key events in life’s history 297 The actual ages of rocks and fossils mark geologic time 298 The fossil record documents the history of life 298

Mechanisms of Macroevolution 300 15.7 15.8

Continental drift has played a major role in macroevolution 300 Connection Plate tectonics may imperil human life 302

Contents

xxvii

15.9 15.10 15.11 15.12 15.13

During mass extinctions, large numbers of species are lost 302 Adaptive radiations have increased the diversity of life 304 Genes that control development play a major role in evolution 304 Evolutionary novelties may arise in several ways 306 Evolution Connection Evolutionary trends do not mean that evolution is goal directed 307

Phylogeny and the Tree of Life 308 15.14 15.15 15.16 15.17 15.18 15.19

16.12 Connection Bacteria can be used as biological

weapons 329

Protists 330 16.13 16.14 16.15 16.16

Phylogenies based on homologies reflect evolutionary history 308 Systematics connects classification with evolutionary history 308 Shared characters are used to construct phylogenetic trees 310 An organism’s evolutionary history is documented in its genome 312 Molecular clocks help track evolutionary time 313 Constructing the tree of life is a work in progress 314

16.17 16.18 16.19 16.20 16.21

Protists are an extremely diverse assortment of eukaryotes 330 Evolution Connection Secondary endosymbiosis is the key to much of protist diversity 331 Chromalveolates represent the range of protist diversity 332 Connection Can algae provide a renewable source of energy? 333 Rhizarians include a variety of amoebas 334 Some excavates have modified mitochondria 334 Unikonts include protists that are closely related to fungi and animals 335 Archaeplastids include red algae, green algae, and land plants 336 Evolution Connection Multicellularity evolved several times in eukaryotes 337

Chapter Review 338

Chapter Review 315

17 The Evolution of Plant

UNIT IV

The Evolution of Biological Diversity

and Fungal Diversity

Plant Evolution and Diversity 17.1 17.2

16 Microbial Life:

Prokaryotes and Protists

Prokaryotes 16.1 16.2 16.3

16.4 16.5 16.6 16.7 16.8 16.9 16.10 16.11

xxviii

318

320 Prokaryotes are diverse and widespread 320 External features contribute to the success of prokaryotes 320 Populations of prokaryotes can adapt rapidly to changes in the environment 322 Prokaryotes have unparalleled nutritional diversity 323 Connection Biofilms are complex associations of microbes 324 Connection Prokaryotes help clean up the environment 324 Bacteria and archaea are the two main branches of prokaryotic evolution 325 Archaea thrive in extreme environments—and in other habitats 326 Bacteria include a diverse assemblage of prokaryotes 326 Connection Some bacteria cause disease 328 Scientific Discovery Koch’s postulates are used to prove that a bacterium causes a disease 328

Contents

340

342 Plants have adaptations for life on land 342 Plant diversity reflects the evolutionary history of the plant kingdom 344

Alternation of Generations and Plant Life Cycles 346 17.3 17.4 17.5 17.6 17.7 17.8 17.9

17.10

17.11

Haploid and diploid generations alternate in plant life cycles 346 The life cycle of a moss is dominated by the gametophyte 346 Ferns, like most plants, have a life cycle dominated by the sporophyte 347 Seedless vascular plants dominated vast “coal forests” 348 A pine tree is a sporophyte with gametophytes in its cones 348 The flower is the centerpiece of angiosperm reproduction 350 The angiosperm plant is a sporophyte with gametophytes in its flowers 350 The structure of a fruit reflects its function in seed dispersal 352 Connection Angiosperms sustain us—and add spice to our diets 352

17.12 Evolution Connection

Pollination by animals has influenced angiosperm evolution 353

17.13 Connection Plant diversity is vital to the future of the

world’s food supply

Diversity of Fungi 355 17.14 17.15 17.16 17.17 17.18 17.19 17.20 17.21

18.14

354

Fungi absorb food after digesting it outside their bodies 355 Fungi produce spores in both asexual and sexual life cycles 356 Fungi are classified into five groups 356 Fungal groups differ in their life cycles and reproductive structures 358 Connection Parasitic fungi harm plants and animals 359 Connection Fungi have enormous ecological benefits 360 Connection Fungi have many practical uses 360 Lichens are symbiotic associations of fungi and photosynthetic organisms 361

Animal Phylogeny and Diversity Revisited 384 18.15 18.16

19 The Evolution of

Vertebrate Diversity

19.1

18 The Evolution of Invertebrate

19.3

18.1 18.2

364

18.3

18.4

What is an animal? 366 Animal diversification began more than half a billion years ago 367 Animals can be characterized by basic features of their “body plan” 368 The body plans of animals can be used to build phylogenetic trees 369

Invertebrate Diversity 370 18.5 18.6 18.7 18.8 18.9 18.10 18.11 18.12 18.13

Sponges have a relatively simple, porous body 370 Cnidarians are radial animals with tentacles and stinging cells 371 Flatworms are the simplest bilateral animals 372 Nematodes have a pseudocoelom and a complete digestive tract 373 Diverse molluscs are variations on a common body plan 374 Annelids are segmented worms 376 Arthropods are segmented animals with jointed appendages and an exoskeleton 378 Evolution Connection Insects are the most successful group of animals 380 Echinoderms have spiny skin, an endoskeleton, and a water vascular system for movement 382

388

Vertebrate Evolution and Diversity 390

19.2

Animal Evolution and Diversity 366

An animal phylogenetic tree is a work in progress 384 Evolution Connection The genes that build animal bodies are ancient 384

Chapter Review 386

Chapter Review 362

Diversity

Our own phylum, Chordata, is distinguished by four features 383

19.4

19.5 19.6 19.7 19.8

Derived characters define the major clades of chordates 390 Hagfishes and lampreys lack hinged jaws 391 Jawed vertebrates with gills and paired fins include sharks, ray-finned fishes, and lobe-finned fishes 392 Evolution Connection New fossil discoveries are filling in the gaps of tetrapod evolution 394 Amphibians are tetrapods—vertebrates with two pairs of limbs 396 Reptiles are amniotes—tetrapods with a terrestrially adapted egg 397 Birds are feathered reptiles with adaptations for flight 398 Mammals are amniotes that have hair and produce milk 399

Primate Diversity 400 19.9 19.10

The human story begins with our primate heritage 400 Humans and four other groups of apes are classified as anthropoids 402

Hominin Evolution 19.11 19.12 19.13 19.14 19.15 19.16 19.17

403 The hominin branch of the primate tree includes species that coexisted 403 Australopiths were bipedal and had small brains 404 Larger brains mark the evolution of Homo 405 From origins in Africa, Homo sapiens spread around the world 406 Who were the “hobbits”? 406 Evolution Connection Human skin color reflects adaptations to varying amounts of sunlight 407 Connection Our knowledge of animal diversity is far from complete 408

Chapter Review 409

Contents

xxix

The Human Digestive System 433

UNIT V

Animals: Form and Function

21.4 21.5 21.6

20 Unifying Concepts of Animal Structure and Function

21.7

412

21.8

Structure and Function in Animal Tissues 20.1 20.2 20.3 20.4

20.5

20.6 20.7

414 Structure fits function at all levels of organization in the animal body 414 Evolution Connection An animal’s form reflects natural selection 415 Tissues are groups of cells with a common structure and function 415 Epithelial tissue covers the body and lines its organs and cavities 416 Connective tissue binds and supports other tissues 417 Muscle tissue functions in movement 418 Nervous tissue forms a communication network 418

Organs and Organ Systems 20.8 20.9 20.10 20.11 20.12

419 Organs are made up of tissues 419 Connection Bioengineers are learning to produce tissues and organs for transplants 419 Organ systems work together to perform life’s functions 420 Connection New imaging technology reveals the inner body 422 The integumentary system protects the body 423

External Exchange and Internal Regulation 20.13 20.14 20.15

424 Structural adaptations enhance exchange with the environment 424 Animals regulate their internal environment 425 Homeostasis depends on negative feedback 426

Chapter Review 426

21 Nutrition and Digestion Obtaining and Processing Food 430 21.1

21.2

21.3

xxx

Animals obtain and ingest their food in a variety of ways 430 Overview: Food processing occurs in four stages 431 Digestion occurs in specialized compartments 432

Contents

21.9 21.10 21.11 21.12 21.13

Nutrition 21.14 21.15 21.16 21.17 21.18 21.19 21.20 21.21 21.22

442 Overview: An animal’s diet must satisfy three needs 442 Chemical energy powers the body 442 An animal’s diet must supply essential nutrients 443 A healthy human diet includes 13 vitamins and many essential minerals 444 Scientific Discovery Scientists use observations and experiments to determine nutritional needs 446 Connection Food labels provide nutritional information 446 Evolution Connection The human health problem of obesity may reflect our evolutionary past 447 Connection What are the health risks and benefits of weight loss plans? 448 Connection Diet can influence risk of cardiovascular disease and cancer 449

Chapter Review 450

22 Gas Exchange

452

Mechanisms of Gas Exchange 454 22.1

428

The human digestive system consists of an alimentary canal and accessory glands 433 Digestion begins in the oral cavity 434 After swallowing, peristalsis moves food through the esophagus to the stomach 434 Connection The Heimlich maneuver can save lives 435 The stomach stores food and breaks it down with acid and enzymes 436 Connection Digestive ailments include acid reflux and gastric ulcers 437 The small intestine is the major organ of chemical digestion and nutrient absorption 438 One of the liver’s many functions is processing nutrient-laden blood from the intestines 440 The large intestine reclaims water and compacts the feces 440 Evolution Connection Evolutionary adaptations of vertebrate digestive systems relate to diet 441

22.2 22.3 22.4 22.5

Overview: Gas exchange in humans involves breathing, transport of gases, and exchange with body cells 454 Animals exchange O2 and CO2 across moist body surfaces 454 Gills are adapted for gas exchange in aquatic environments 456 The tracheal system of insects provides direct exchange between the air and body cells 457 Evolution Connection The evolution of lungs facilitated the movement of tetrapods onto land 458

The Human Respiratory System 458 22.6

In mammals, branching tubes convey air to lungs located in the chest cavity 458

22.7 22.8 22.9

Connection Smoking is a serious assault on the

respiratory system 460 Negative pressure breathing ventilates your lungs 460 Breathing is automatically controlled 461

24 The Immune System Innate Immunity 486 24.1

Transport of Gases in the Human Body 462 22.10 22.11 22.12

Blood transports respiratory gases 462 Hemoglobin carries O2, helps transport CO2, and buffers the blood 462 Connection The human fetus exchanges gases with the mother’s blood 463

24.2 24.3

24.4

466

24.5 24.6

Circulatory Systems 23.1 23.2

468 Circulatory systems facilitate exchange with all body tissues 468 Evolution Connection Vertebrate cardiovascular systems reflect evolution 469

The Human Cardiovascular System and Heart 470 23.3

23.4

23.5 23.6

The human cardiovascular system illustrates the double circulation of mammals 470 The heart contracts and relaxes rhythmically 471 The SA node sets the tempo of the heartbeat 472 Connection What is a heart attack? 473

Structure and Function of Blood Vessels 23.7 23.8 23.9 23.10 23.11

All animals have innate immunity 486 Inflammation mobilizes the innate immune response 487 The lymphatic system becomes a crucial battleground during infection 488

Adaptive Immunity 489

Chapter Review 464

23 Circulation

474 The structure of blood vessels fits their functions 474 Blood pressure and velocity reflect the structure and arrangement of blood vessels 475 Connection Measuring blood pressure can reveal cardiovascular problems 476 Smooth muscle controls the distribution of blood 477 Capillaries allow the transfer of substances through their walls 478

24.7 24.8 24.9 24.10 24.11 24.12 24.13 24.14 24.15

The adaptive immune response counters specific invaders 489 Lymphocytes mount a dual defense 490 Antigens have specific regions where antibodies bind to them 491 Clonal selection musters defensive forces against specific antigens 492 Antibodies are the weapons of the humoral immune response 494 Antibodies mark antigens for elimination 495 Connection Monoclonal antibodies are powerful tools in the lab and clinic 496 Helper T cells stimulate the humoral and cell-mediated immune responses 497 Cytotoxic T cells destroy infected body cells 498 Connection HIV destroys helper T cells, compromising the body’s defenses 498 Evolution Connection The rapid evolution of HIV complicates AIDS treatment 499 The immune system depends on our molecular fingerprints 500

Disorders of the Immune System 500 24.16 Connection Malfunction or failure of the immune system 24.17

causes disease 500 Connection Allergies are overreactions to certain environmental antigens 501

Chapter Review 502

25 Control of Body Temperature and Water Balance

Structure and Function of Blood

Thermoregulation

23.12

25.1

23.13 23.14 23.15

479 Blood consists of red and white blood cells suspended in plasma 479 Connection Too few or too many red blood cells can be unhealthy 480 Blood clots plug leaks when blood vessels are injured 480 Connection Stem cells offer a potential cure for blood cell diseases 481

Chapter Review 482

484

25.2 25.3

504

506 An animal’s regulation of body temperature helps maintain homeostasis 506 Heat is gained or lost in four ways 506 Thermoregulation involves adaptations that balance heat gain and loss 506 Contents

xxxi

Osmoregulation and Excretion 508 25.4 25.5 25.6 25.7 25.8 25.9 25.10

27.2

Animals balance the level of water and solutes through osmoregulation 508 Evolution Connection A variety of ways to dispose of nitrogenous wastes has evolved in animals 509 The urinary system plays several major roles in homeostasis 510 Overview: The key processes of the urinary system are filtration, reabsorption, secretion, and excretion 511 Blood filtrate is refined to urine through reabsorption and secretion 512 Hormones regulate the urinary system 513 Connection Kidney dialysis can be lifesaving 513

Human Reproduction 536 27.3 27.4 27.5 27.6 27.7

Reproductive anatomy of the human female 536 Reproductive anatomy of the human male 538 The formation of sperm and egg cells requires meiosis 540 Hormones synchronize cyclic changes in the ovary and uterus 542 Connection Sexual activity can transmit disease 544 Connection Contraception can prevent unwanted pregnancy 545

Chapter Review 514

27.8

26 Hormones and the

Principles of Embryonic Development 546

Endocrine System

27.9

516

27.10

The Nature of Chemical Regulation 518 26.1

26.2

27.11 27.12

Chemical signals coordinate body functions 518 Hormones affect target cells using two main signaling mechanisms 519

27.13 27.14

26.3 26.4

27.15

Overview: The vertebrate endocrine system consists of more than a dozen major glands 520 The hypothalamus, which is closely tied to the pituitary, connects the nervous and endocrine systems 522

27.16 27.17 27.18

Hormones and Homeostasis 524 26.5 26.6 26.7 26.8 26.9 26.10 26.11

Fertilization results in a zygote and triggers embryonic development 546 Cleavage produces a ball of cells from the zygote 548 Gastrulation produces a three-layered embryo 549 Organs start to form after gastrulation 550 Multiple processes give form to the developing animal 552 Evolution Connection Pattern formation during embryonic development is controlled by ancient genes 552

Human Development 554

The Vertebrate Endocrine System 520

The thyroid regulates development and metabolism 524 Hormones from the thyroid and parathyroid glands maintain calcium homeostasis 524 Pancreatic hormones regulate blood glucose levels 526 Connection Diabetes is a common endocrine disorder 527 The adrenal glands mobilize responses to stress 528 The gonads secrete sex hormones 529 Evolution Connection A single hormone can perform a variety of functions in different animals 530

The embryo and placenta take shape during the first month of pregnancy 554 Human development from conception to birth is divided into three trimesters 556 Childbirth is induced by hormones and other chemical signals 558 Connection Reproductive technologies increase our reproductive options 559

Chapter Review 560

28 Nervous Systems 28.1

Nervous systems receive sensory input, interpret it, and send out appropriate commands 564 Neurons are the functional units of nervous systems 565

28.2

27 Reproduction and

Nerve Signals and Their Transmission 566

532

28.3

Asexual and Sexual Reproduction 534 27.1

Asexual reproduction results in the generation of genetically identical offspring 534

Contents

562

Nervous System Structure and Function 564

Chapter Review 530

Embryonic Development

xxxii

Sexual reproduction results in the generation of genetically unique offspring 534

28.4

Nerve function depends on charge differences across neuron membranes 566 A nerve signal begins as a change in the membrane potential 566

28.5 28.6 28.7 28.8 28.9

The action potential propagates itself along the axon 568 Neurons communicate at synapses 569 Chemical synapses enable complex information to be processed 570 A variety of small molecules function as neurotransmitters 570 Connection Many drugs act at chemical synapses 571

29.6

Vision 29.7 29.8 29.9 29.10

An Overview of Animal Nervous Systems 572 28.10 Evolution Connection The evolution of animal nervous 28.11 28.12 28.13

systems reflects changes in body symmetry 572 Vertebrate nervous systems are highly centralized 573 The peripheral nervous system of vertebrates is a functional hierarchy 574 The vertebrate brain develops from three anterior bulges of the neural tube 576

The Human Brain 28.14 28.15 28.16 28.17 28.18 28.19 28.20

576 The structure of a living supercomputer: The human brain 576 The cerebral cortex is a mosaic of specialized, interactive regions 578 Connection Injuries and brain operations provide insight into brain function 579 Connection fMRI scans provide insight into brain structure and function 580 Several parts of the brain regulate sleep and arousal 580 The limbic system is involved in emotions, memory, and learning 581 Connection Changes in brain physiology can produce neurological disorders 582

29.11 29.12 29.13

586

Sensory Reception 588 29.1

29.2

29.3

Sensory organs share a common cellular basis 588 Sensory receptors convert stimulus energy to action potentials 588 Specialized sensory receptors detect five categories of stimuli 590

29.5

592 The ear converts air pressure waves to action potentials that are perceived as sound 592 The inner ear houses our organs of balance 594

Evolution Connection Several types of eyes have evolved independently among animals 595 Humans have single-lens eyes that focus by changing position or shape 596 Connection Artificial lenses or surgery can correct focusing problems 597 The human retina contains two types of photoreceptors: rods and cones 598

Taste and odor receptors detect chemicals present in solution or air 599 Connection “Supertasters” have a heightened sense of taste 599 Review: The central nervous system couples stimulus with response 600

30 How Animals Move

602

Movement and Locomotion 604 30.1 30.2

Locomotion requires energy to overcome friction and gravity 604 Skeletons function in support, movement, and protection 606

The Vertebrate Skeleton 608 30.3

30.6

Evolution Connection Vertebrate skeletons are variations on an ancient theme 608 Bones are complex living organs 609 Connection Healthy bones resist stress and heal from injuries 610 Joints permit different types of movement 611

Muscle Contraction and Movement 611 30.7

30.8 30.9 30.10 30.11

Hearing and Balance 29.4

595

Chapter Review 600

30.5

29 The Senses

594

Taste and Smell 599

30.4

Chapter Review 584

Connection What causes motion sickness?

30.12

The skeleton and muscles interact in movement 611 Each muscle cell has its own contractile apparatus 612 A muscle contracts when thin filaments slide along thick filaments 612 Motor neurons stimulate muscle contraction 614 Connection Aerobic respiration supplies most of the energy for exercise 615 Connection Characteristics of muscle fiber affect athletic performance 616

Chapter Review 617

Contents

xxxiii

UNIT VI

32.4

Plants: Form and Function

32.5

Plant Nutrients and the Soil 650 32.6

31 Plant Structure, Growth, and Reproduction

Plant Structure and Function 31.1

31.2

31.3

31.4 31.5 31.6

32.7

620

32.8 32.9

622

32.10

Connection People have

manipulated plants since prehistoric times 622 The two major groups of angiosperms are the monocots and the eudicots 623 A typical plant body contains three basic organs: roots, stems, and leaves 624 Many plants have modified roots, stems, and leaves 625 Three tissue systems make up the plant body 626 Plant cells are diverse in structure and function 628

32.11

31.8

32.12 32.13 32.14

31.10 31.11 31.12 31.13 31.14 31.15

33 Control Systems in Plants

Primary growth lengthens roots and shoots 630 Secondary growth increases the diameter of woody plants 632 The flower is the organ of sexual reproduction in angiosperms 634 The development of pollen and ovules culminates in fertilization 635 The ovule develops into a seed 636 The ovary develops into a fruit 637 Seed germination continues the life cycle 638 Asexual reproduction produces plant clones 638 Evolution Connection Evolutionary adaptations allow some trees to live very long lives 640

33.1

33.2

33.3 33.4 33.5

33.7

The Uptake and Transport of Plant Nutrients 644 32.1

32.2

32.3

xxxiv

Plants acquire nutrients from air, water, and soil 644 The plasma membranes of root cells control solute uptake 645 Transpiration pulls water up xylem vessels 646

Contents

642

660

Plant Hormones 662

33.6

Chapter Review 640

32 Plant Nutrition and Transport

Most plants depend on bacteria to supply nitrogen 655 Evolution Connection Plants have evolved symbiotic relationships that are mutually beneficial 656 The plant kingdom includes epiphytes, parasites, and carnivores 657

Chapter Review 658

Reproduction of Flowering Plants 634 31.9

Plant health depends on a complete diet of essential inorganic nutrients 650 Connection Fertilizers can help prevent nutrient deficiencies 651 Fertile soil supports plant growth 652 Connection Soil conservation is essential to human life 653 Connection Organic farmers follow principles of sustainable agriculture 654 Connection Agricultural research is improving the yields and nutritional values of crops 654

Plant Nutrition and Symbiosis 655

Plant Growth 630 31.7

Guard cells control transpiration 647 Phloem transports sugars 648

33.8

Experiments on how plants turn toward light led to the discovery of a plant hormone 662 Five major types of hormones regulate plant growth and development 664 Auxin stimulates the elongation of cells in young shoots 664 Cytokinins stimulate cell division 666 Gibberellins affect stem elongation and have numerous other effects 666 Abscisic acid inhibits many plant processes 667 Ethylene triggers fruit ripening and other aging processes 668 Connection Plant hormones have many agricultural uses 669

Responses to Stimuli 670 33.9 33.10 33.11 33.12 33.13

Tropisms orient plant growth toward or away from environmental stimuli 670 Plants have internal clocks 671 Plants mark the seasons by measuring photoperiod 672 Phytochromes are light detectors that may help set the biological clock 673 Evolution Connection Defenses against herbivores and infectious microbes have evolved in plants 674

Chapter Review 675

UNIT VII

Ecology

34 The Biosphere:

An Introduction to Earth’s Diverse Environments 678

35 Behavioral Adaptations to the Environment

The Scientific Study of Behavior 700 35.1

35.2

The Biosphere 680 34.1 34.2 34.3 34.4

34.5

Ecologists study how organisms interact with their environment at several levels 680 Connection The science of ecology provides insight into environmental problems 681 Physical and chemical factors influence life in the biosphere 682

Aquatic Biomes 686 34.6

34.7

35.3

Sunlight and substrate are key factors in the distribution of marine organisms 686 Current, sunlight, and nutrients are important abiotic factors in freshwater biomes 688

35.4 35.5 35.6 35.7 35.8 35.9 35.10 35.11

34.9 34.10 34.11 34.12 34.13 34.14 34.15 34.16 34.17 34.18

Terrestrial biomes reflect regional variations in climate 689 Tropical forests cluster near the equator 690 Savannas are grasslands with scattered trees 690 Deserts are defined by their dryness 691 Spiny shrubs dominate the chaparral 692 Temperate grasslands include the North American prairie 692 Broadleaf trees dominate temperate forests 693 Coniferous forests are often dominated by a few species of trees 693 Long, bitter-cold winters characterize the tundra 694 Polar ice covers the land at high latitudes 694 The global water cycle connects aquatic and terrestrial biomes 695

Chapter Review 696

703 Habituation is a simple type of learning 703 Imprinting requires both innate behavior and experience 704 Connection Imprinting poses problems and opportunities for conservation programs 705 Animal movement may be a simple response to stimuli or require spatial learning 706 Movements of animals may depend on cognitive maps 707 Animals may learn to associate a stimulus or behavior with a response 708 Social learning employs observation and imitation of others 708 Problem-solving behavior relies on cognition 709

Survival and Reproductive Success 710 35.12 35.13 35.14

Terrestrial Biomes 689 34.8

Behavioral ecologists ask both proximate and ultimate questions 700 Fixed action patterns are innate behaviors 700 Behavior is the result of both genetic and environmental factors 702

Learning

Evolution Connection

Organisms are adapted to abiotic and biotic factors by natural selection 683 Regional climate influences the distribution of terrestrial communities 684

698

35.15 35.16

Behavioral ecologists use cost-benefit analysis to study foraging 710 Communication is an essential element of interactions between animals 711 Mating behavior often includes elaborate courtship rituals 712 Mating systems and parental care enhance reproductive success 713 Connection Chemical pollutants can cause abnormal behavior 714

Social Behavior and Sociobiology 715 35.17 35.18 35.19 35.20 35.21 35.22 35.23

Sociobiology places social behavior in an evolutionary context 715 Territorial behavior parcels out space and resources 715 Agonistic behavior often resolves confrontations between competitors 716 Dominance hierarchies are maintained by agonistic behavior 716 Evolution Connection Altruistic acts can often be explained by the concept of inclusive fitness 717 Scientific Discovery Jane Goodall revolutionized our understanding of chimpanzee behavior 718 Human behavior is the result of both genetic and environmental factors 719

Chapter Review 720 Contents

xxxv

36 Population Ecology

37.6

722

37.7

Population Structure and Dynamics 724 36.1

36.2

36.3 36.4 36.5 36.6 36.7 36.8

37.8

Population ecology is the study of how and why populations change 724 Density and dispersion patterns are important population variables 724 Life tables track survivorship in populations 725 Idealized models predict patterns of population growth 726 Multiple factors may limit population growth 728 Some populations have “boom-and-bust” cycles 729 Evolution Connection Evolution shapes life histories 730 Connection Principles of population ecology have practical applications 731

37.9 37.10 37.11 37.12 37.13

Ecosystem Structure and Dynamics 750 37.14 37.15 37.16 37.17

The Human Population 36.9 36.10 36.11

732 The human population continues to increase, but the growth rate is slowing 732 Connection Age structures reveal social and economic trends 734 Connection An ecological footprint is a measure of resource consumption 734

37.18 37.19 37.20 37.21 37.22

Chapter Review 736

37 Communities and Ecosystems Community Structure and Dynamics 740 37.1

37.2

37.3

37.4 37.5

xxxvi

A community includes all the organisms inhabiting a particular area 740 Interspecific interactions are fundamental to community structure 740 Competition may occur when a shared resource is limited 741 Mutualism benefits both partners 741 Evolution Connection Predation leads to diverse adaptations in prey species 742

Contents

Evolution Connection Herbivory leads to diverse adaptations in plants 742 Parasites and pathogens can affect community composition 743 Trophic structure is a key factor in community dynamics 744 Food chains interconnect, forming food webs 745 Species diversity includes relative abundance and species richness 746 Keystone species have a disproportionate impact on diversity 747 Disturbance is a prominent feature of most communities 748 Connection Invasive species can devastate communities 749

37.23

738

Ecosystem ecology emphasizes energy flow and chemical cycling 750 Primary production sets the energy budget for ecosystems 750 Energy supply limits the length of food chains 751 Connection A pyramid of production explains the ecological cost of meat 752 Chemicals are cycled between organic matter and abiotic reservoirs 752 The carbon cycle depends on photosynthesis and respiration 753 The phosphorus cycle depends on the weathering of rock 754 The nitrogen cycle depends on bacteria 754 Connection A rapid inflow of nutrients degrades aquatic ecosystems 756 Connection Ecosystem services are essential to human well-being 757

Chapter Review 758

38 Conservation Biology

760

The Loss of Biodiversity 762 38.1 38.2

38.3 38.4 38.5 38.6

Loss of biodiversity includes the loss of ecosystems, species, and genes 762 Connection Habitat loss, invasive species, overharvesting, pollution, and climate change are major threats to biodiversity 764 Connection Rapid warming is changing the global climate 766 Connection Human activities are responsible for rising concentrations of greenhouse gases 767 Global climate change affects biomes, ecosystems, communities, and populations 768 Evolution Connection Climate change is an agent of natural selection 769

Conservation Biology and Restoration Ecology 770 38.7 38.8 38.9 38.10 38.11

38.12 38.13

Protecting endangered populations is one goal of conservation biology 770 Sustaining ecosystems and landscapes is a conservation priority 771 Establishing protected areas slows the loss of biodiversity 772 Zoned reserves are an attempt to reverse ecosystem disruption 773 Connection The Yellowstone to Yukon Conservation Initiative seeks to preserve biodiversity by connecting protected areas 774 Connection The study of how to restore degraded habitats is a developing science 776 Sustainable development is an ultimate goal 777

Appendix 1 Metric Conversion Table Appendix 2 The Periodic Table

A-2

Appendix 3 The Amino Acids of Proteins Appendix 4 Chapter Review Answers Appendix 5 Credits Glossary

Index

A-1

A-3 A-4

A-26

G-1 I-1

Chapter Review 778

Contents

xxxvii

C H A P T E R

1

Biology: Exploring Life

BIG IDEAS

Themes in the Study of Biology (1.1–1.4)

Common themes help to organize the study of life.

Evolution, the Core Theme of Biology (1.5–1.7)

Evolution accounts for the unity and diversity of life and the evolutionary adaptations of organisms to their environment.

The Process of Science (1.8–1.9)

In studying nature, scientists make observations, form hypotheses, and test predictions with experiments.

Biology and Everyday Life (1.10–1.11)

Learning about biology helps us understand many issues involving science, technology, and society.

his young lemur spends much of its time on its mother’s back. But it is also groomed and cared for by other females of the troop, a group of about 15 members led by a dominant female. About the size of large cats, these ring-tailed lemurs (scientific name, Lemur catta) are noted for their distinctive tails, dark eye patches and muzzle, and, as you can see on the cover of this book, entrancing eyes. They are also highly vocal primates, with 28 distinct calls, such as “predator alert,” “stay out of my territory,” and purrs of contentment. About 33 species of lemurs live on the island of Madagascar, and before humans arrived 2,000 years ago, there were even more. The size of Texas, Madagascar is located about 400 km (240 miles) off the southeast coast of Africa. It is home to many plants and animals found nowhere else in the world. Its geographic history helps explain its remarkable biodiversity.

T

Madagascar was once part of a supercontinent that began breaking apart about 150 million years ago—before the primates (lemurs, monkeys, apes, and humans) had evolved. Apparently, 60 million years ago, ancestral lemurs floated on logs or vegetation from Africa to the island. Their new home was relatively free of predators and competitors and offered many different habitats, from tropical forests to deserts to highlands with spiny shrubs. Over millions of years, lemurs diversified on this isolated island. The wonderful assortment of lemurs on Madagascar is the result of evolution, the process that has transformed life on Earth from its earliest beginnings to the diversity of organisms living today. In this chapter, we begin our exploration of biology—the scientific study of life, its evolution, and its amazing diversity. 1

Themes in the Study of Biology 1.1 All forms of life share common properties

(1) Order. This close-up of a sunflower illustrates the highly ordered structure that typifies life. Living cells are the basis of this complex organization. (2) Reproduction. Organisms reproduce their own kind. Here an emperor penguin protects its baby. (3) Growth and development. Inherited information in the form of DNA controls the pattern of growth and development of all organisms, including this hatching crocodile. (4) Energy processing. When this bear eats its catch, it will use the chemical energy stored in the fish to power its own activities and chemical reactions. (5) Response to the environment. All organisms respond to environmental stimuli. This Venus flytrap closed its trap rapidly in response to the stimulus of a damselfly landing on it. (6) Regulation. Many types of mechanisms regulate an organism’s internal environment, keeping it within limits that sustain life. Pictured here is a typical lemur behavior with a regulatory function—“sunbathing”—which helps raise the animal’s body temperature on cold mornings.

(7) Evolutionary adaptation. The leaflike appearance of this katydid camouflages it in its environment. Such adaptations evolve over many generations as individuals with traits best suited to their environment have greater reproductive success and pass their traits to offspring. Figure 1.1 reminds us that the living world is wondrously varied. How do biologists make sense of this diversity and complexity, and how can you? Indeed, biology is a subject of enormous scope that gets bigger every year. One of the ways to help you organize all this information is to connect what you learn to a set of themes that you will encounter throughout your study of life. The next few modules introduce several of these themes: novel properties emerging at each level of biological organization, the cell as the fundamental unit of life, the correlation of structure and function, and the exchange of matter and energy as organisms interact with the environment. We then focus on the core theme of biology—evolution, the theme that makes sense of both the unity and diversity of life. And in the final two sections of the chapter, we look at the process of science and the relationship of biology to our everyday lives. Let’s begin our journey with a tour through the levels of the biological hierarchy.

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How would you define life?

● Life can be defined by a set of common properties such as those described in this module.

Defining biology as the scientific study of life raises the obvious question: What is life? How would you describe what distinguishes living things from nonliving things? Even a small child realizes that a bug or a flower is alive, while a rock or water is not. They, like all of us, recognize life mainly by what living things do. Figure 1.1 highlights seven of the properties and processes that we associate with life.

(1) Order

(3) Growth and development

(4) Energy processing (2) Reproduction

(5) Response to the environment

(6) Regulation

 Figure 1.1 Some important properties of life

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(7) Evolutionary adaptation

1.2 In life’s hierarchy of organization, new properties emerge at each level As Figure 1.2 illustrates, the study of life extends from the global scale of the biosphere to the microscopic scale of molecules. At the upper left we take a distant view of the biosphere, all of the environments on Earth that support life. These include most regions of land, bodies of water, and the lower atmosphere. Ecosystem Forest in Madagascar

Biosphere Madagascar

Community All organisms in the forest

Population Group of ring-tailed lemurs

Organism Ring-tailed lemur

Spinal cord Organ system Nervous system Brain

Organ Brain

Nerve

Tissue Nervous tissue

A closer look at one of these environments brings us to the level of an ecosystem, which consists of all the organisms living in a particular area, as well as the physical components with which the organisms interact, such as air, soil, water, and sunlight. The entire array of organisms in an ecosystem is called a community. The community in this forest ecosystem in Madagascar includes the lemurs and the agave plant they are eating, as well as birds, snakes, and catlike carnivores called civets; a huge diversity of insects; many kinds of trees and other plants; fungi; and enormous numbers of microscopic protists and bacteria. Each unique form of life is called a species. A population includes all the individuals of a particular species living in an area, such as all the ring-tailed lemurs in the forest community. Next in the hierarchy is the organism, an individual living thing. Within a complex organism such as a lemur, life’s hierarchy continues to unfold. An organ system, such as the circulatory system or nervous system, consists of several organs that cooperate in a specific function. For instance, the organs of the nervous system are the brain, the spinal cord, and the nerves. A lemur’s nervous system controls its actions, such as climbing trees. An organ is made up of several different tissues, each made up of a group of similar cells that perform a specific function. A cell is the fundamental unit of life. In the nerve cell shown here, you can see several organelles, such as the nucleus. An organelle is a membrane-enclosed structure that performs a specific function in a cell. Finally, we reach the level of molecules in the hierarchy. A molecule is a cluster of small chemical units called atoms held together by chemical bonds. Our example in Figure 1.2 is a computer graphic of a section of DNA (deoxyribonucleic acid)—the molecule of inheritance. Now let’s work our way in the opposite direction in Figure 1.2, moving up life’s hierarchy from molecules to the biosphere. It takes many molecules to build organelles, numerous organelles to make a cell, many cells to make a tissue, and so on. At each new level, there are novel properties that arise, properties that were not present at the preceding level. For example, life emerges at the level of the cell—a test tube full of organelles is not alive. Such emergent properties represent an important theme of biology. The familiar saying that “the whole is greater than the sum of its parts” captures this idea. The emergent properties of each level result from the specific arrangement and interactions of its parts.

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Which of these levels of biological organization includes all others in the list: cell, molecule, organ, tissue? ● Organ

Cell Nerve cell

Organelle Nucleus

 Figure 1.2 Life’s hierarchy of organization

Atom

Nucleus

Molecule DNA

Themes in the Study of Biology

3

1.3 Cells are the structural and functional units of life

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Prokaryotic cell

Eukaryotic cell

DNA (no nucleus) Membrane

Organelles

Colorized TEM 11,250⫻

Nucleus (membraneenclosed) DNA (throughout nucleus)

 Figure 1.3 Contrasting the size and complexity of prokaryotic and eukaryotic cells (shown here approximately 11,250 times their real size)

generally fits function. A screwdriver tightens or loosens screws, a hammer pounds nails. Because of their form, these tools can’t do each other’s jobs. Applied to biology, this theme of form fitting function is a guide to the structure of life at all its organizational levels. For example, the long extension of the nerve cell shown in Figure 1.2 enables it to transmit impulses across long distances in the body. Often, analyzing a biological structure gives us clues about what it does and how it works. The activities of organisms are all based on cells. For example, your every thought is based on the actions of nerve cells, and your movements depend on muscle cells. Even a global process such as the cycling of carbon is the result of cellular activities, including the photosynthesis of plant cells and the cellular respiration of nearly all cells, a process that uses oxygen to break down sugar for energy and releases carbon dioxide. In the next module, we explore these processes and how they relate to the theme of organisms interacting with their environments.

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Why are cells considered the basic units of life?

● They are the lowest level in the hierarchy of biological organization at which the properties of life emerge.

The cell has a special place in the hierarchy of biological organization. It is the level at which the properties of life emerge—the lowest level of structure that can perform all activities required for life. A cell can regulate its internal environment, take in and use energy, respond to its environment, and develop and maintain its complex organization. The ability of cells to give rise to new cells is the basis for all reproduction and for the growth and repair of multicellular organisms. All organisms are composed of cells. They occur singly as a great variety of unicellular (single-celled) organisms, such as amoebas and most bacteria. And cells are the subunits that make up multicellular organisms, such as lemurs and trees. Your body consists of trillions of cells of many different kinds. All cells share many characteristics. For example, every cell is enclosed by a membrane that regulates the passage of materials between the cell and its surroundings. And every cell uses DNA as its genetic information. There are two basic types of cells. Prokaryotic cells were the first to evolve and were Earth’s sole inhabitants for about the first 1.5 billion years of life on Earth. Fossil evidence indicates that eukaryotic cells evolved about 2.1 billion years ago. Figure 1.3 shows these two types of cells as artificially colored photographs taken with an electron microscope. A prokaryotic cell is much simpler and usually much smaller than a eukaryotic cell. The cells of the microorganisms we call bacteria are prokaryotic. Plants, animals, fungi, and protists are all composed of eukaryotic cells. As you can see in Figure 1.3, a eukaryotic cell is subdivided by membranes into many functional compartments, called organelles. These include a nucleus, which houses the cell’s DNA. The properties of life emerge from the ordered arrangement and interactions of the structures of a cell. Such a combination of components forms a more complex organization that we can call a system. Cells are examples of biological systems, as are organisms and ecosystems. Systems and their emergent properties are not unique to life. Consider a box of bicycle parts. When all of the individual parts are properly assembled, the result is a mechanical system you can use for exercise or transportation. The emergent properties of life, however, are particularly challenging to study because of the unrivaled complexity of biological systems. At the cutting edge of large-scale research today is an approach called systems biology. The goal of systems biology is to construct models for the dynamic behavior of whole systems based on studying the interactions among the parts. Biological systems can range from the functioning of the biosphere to the molecular machinery of an organelle. Cells illustrate another theme of biology: the correlation of structure and function. Experience shows you that form

1.4 Organisms interact with their environment, exchanging matter and energy and soil to plants, to animals and decomposers, and back to the air and soil (blue arrows in the figure). By contrast, an ecosystem gains and loses energy constantly. Energy flows into the ecosystem when plants and other photosynthesizers absorb light energy from the sun (yellow arrow) and convert it to the chemical energy of sugars and other complex molecules. Chemical energy (orange arrow) is then passed through a series of consumers and, eventually, decomposers, powering each organism in turn. In the process of these energy conversions between and within organisms, some energy is converted to heat, which is then lost from the system (red arrow). In contrast to chemical nutrients, which recycle within an ecosystem, energy flows through an ecosystem, entering as light and exiting as heat. In this first section, we have touched on several themes of biology, from emergent properties in the biological hierarchy of organization, to cells as the structural and functional units of life, to the exchange of matter and energy as organisms interact with their environment. In the next section, we begin our exploration of evolution, the core theme of biology.

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Explain how the photosynthesis of plants functions in both cycling of chemical nutrients and the flow of energy in an ecosystem.

● Photosynthesis uses light to convert carbon dioxide and water to energyrich food, making it the pathway by which both chemical nutrients and energy become available to most organisms.

An organism interacts with its environment, which includes other organisms as well as physical factors. Figure 1.4 is a simplified diagram of such interactions taking place in a forest ecosystem in Madagascar. Plants are the producers that provide the food for a typical ecosystem. A tree, for example, absorbs water (H2O) and minerals from the soil through its roots, and its leaves take in carbon dioxide (CO2) from the air. In photosynthesis, a tree’s leaves use energy from sunlight to convert CO2 and H2O to sugar and oxygen (O2). The leaves release O2 to the air, and the roots help form soil by breaking up rocks. Thus, both organism and environment are affected by the interactions between them. The consumers of the ecosystem eat plants and other animals. The lemur in Figure 1.4 eats the leaves and fruits of the tamarind tree. To release the energy in food, animals (as well as plants and most other organisms) take in O2 from the air and release CO2. An animal’s wastes return other chemicals to the environment. Another vital part of the ecosystem includes the small animals, fungi, and bacteria in the soil that decompose wastes and the remains of dead organisms. These decomposers act as recyclers, changing complex matter into simpler mineral nutrients that plants can absorb and use. The dynamics of ecosystems include two major processes— the recycling of chemical nutrients and the flow of energy. These processes are illustrated in Figure 1.4. The most basic chemicals necessary for life—carbon dioxide, oxygen, water, and various minerals—cycle within an ecosystem from the air

Ecosystem

O2

O2 Sunlight

Heat Consumers (such as animals)

Producers (such as plants) Chemical energy (food)

CO2

CO2

Water and minerals taken up by tree roots

Cycling of chemical nutrients

Decomposers (in soil)

 Figure 1.4 The cycling of nutrients and flow of energy in an ecosystem Themes in the Study of Biology

5

Evolution, the Core Theme of Biology 1.5 The unity of life is based on DNA and a common genetic code

A

T

A C

G

T A

T A

C

G

G

T

C

 Figure 1.5 The four building blocks of DNA (left); part of a DNA double helix (right)

The way DNA encodes a cell’s information is analogous to the way we arrange letters of the alphabet into precise sequences with specific meanings. The word rat, for example, conjures up an image of a rodent; tar and art, which contain the same letters, mean very different things. We can think of the four building blocks as the alphabet of inheritance. Specific sequential arrangements of these four chemical letters encode precise information in genes, which are typically hundreds or thousands of “letters” long. The DNA of genes provides the blueprints for making proteins, and proteins serve as the tools that actually build and maintain the cell and carry out its activities. A bacterial gene may direct the cell to “Make a yellow pigment.” A particular human gene may mean “Make the hormone insulin.” All forms of life use essentially the same genetic code to translate the information stored in DNA into proteins. This makes it possible to engineer cells to produce proteins normally found only in some other organism. Thus, bacteria can be used to produce insulin for the treatment of diabetes by inserting a gene for human insulin into bacterial cells. The diversity of life arises from differences in DNA sequences—in other words, from variations on the common theme of storing genetic information in DNA. Bacteria and humans are different because they have different genes. But both sets of instructions are written in the same language. In the next module, we see how biologists attempt to organize the diversity of life.

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What is the chemical basis for all of life’s kinship? ● DNA as the genetic material

All cells have DNA, and the continuity of life depends on this universal genetic material. DNA is the chemical substance of genes, the units of inheritance that transmit information from parents to offspring. Genes, which are grouped into very long DNA molecules called chromosomes, also control all the activities of a cell. The molecular structure of DNA accounts for these functions. Let us explain: Each DNA molecule is made up of two long chains coiled together into what is called a double helix. The chains are made up of four kinds of chemical building blocks. Figure 1.5 illustrates these four building blocks, called nucleotides, with different colors and letter abA T breviations of their names. The right side of the figC G ure shows a short section C G of a DNA double helix.

1.6 The diversity of life can be arranged into three domains We can think of biology’s enormous scope as having two dimensions. The “vertical” dimension, which we examined in Module 1.2, is the size scale that stretches from molecules to the biosphere. But biology also has a “horizontal” dimension, spanning across the great diversity of organisms existing now and over the long history of life on Earth.

Grouping Species Diversity is a hallmark of life. Biologists have so far identified and named about 1.8 million species, and thousands more are identified each year. Estimates of the total number of species range from 10 million to over 100 million. Whatever the actual number, biologists face a major challenge in attempting to make sense of this enormous variety of life. There seems to be a human tendency to group diverse items according to similarities. We may speak of bears or butterflies, though we recognize that each group includes many different species. We may even sort groups into broader categories, such 6

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as mammals and insects. Taxonomy, the branch of biology that names and classifies species, arranges species into a hierarchy of broader and broader groups, from genus, family, order, class, and phylum, to kingdom.

The Three Domains of Life Until the 1990s, most biologists used a taxonomic scheme that divided all of life into five kingdoms. But new methods for assessing evolutionary relationships, such as comparison of DNA sequences, have led to an ongoing reevaluation of the number and boundaries of kingdoms. As that debate continues, however, there is consensus that life can be organized into three higher levels called domains. Figure 1.6, on the facing page, shows representatives of the three domains: Bacteria, Archaea, and Eukarya. Domains Bacteria and Archaea both consist of prokaryotes, organisms with prokaryotic cells. Most prokaryotes are singlecelled and microscopic. The photos of the prokaryotes in Figure

To which of the three domains of life do we belong? ● Eukarya

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Colorized SEM 6,000⫻

Domain Bacteria

Bacteria

Colorized SEM 7,700⫻

Domain Archaea

Archaea

Domain Eukarya

LM 275⫻

1.6 were made with an electron microscope, and the number along the side indicates the magnification of the image. (We will discuss microscopy in Chapter 4.) Bacteria and archaea were once combined in a single kingdom. But much evidence indicates that they represent two very distinct branches of life, each of which includes multiple kingdoms. Bacteria are the most diverse and widespread prokaryotes. In the photo of bacteria in Figure 1.6, each of the rod-shaped structures is a bacterial cell. Many of the prokaryotes known as archaea live in Earth’s extreme environments, such as salty lakes and boiling hot springs. Each round structure in the photo of archaea in Figure 1.6 is an archaeal cell. All the eukaryotes, organisms with eukaryotic cells, are grouped in domain Eukarya. As you learned in Module 1.3, eukaryotic cells have a nucleus and other internal structures called organelles. Protists are a diverse collection of mostly single-celled organisms and some relatively simple multicellular relatives. Pictured in Figure 1.6 is an assortment of protists in a drop of pond water. Although protists were once placed in a single kingdom, it is now clear that they do not form a single natural group of species. Biologists are currently debating how to split the protists into groups that accurately reflect their evolutionary relationships. The three remaining groups within Eukarya contain multicellular eukaryotes. These kingdoms are distinguished partly by their modes of nutrition. Kingdom Plantae consists of plants, which produce their own food by photosynthesis. The representative of kingdom Plantae in Figure 1.6 is a tropical bromeliad, a plant native to the Americas. Kingdom Fungi, represented by the mushrooms in Figure 1.6, is a diverse group, whose members mostly decompose the remains of dead organisms and organic wastes and absorb the nutrients into their cells. Animals obtain food by ingestion, which means they eat other organisms. Representing kingdom Animalia, the sloth in Figure 1.6 resides in the trees of Central and South American rain forests. There are actually members of two other groups in the sloth photo. The sloth is clinging to a tree (kingdom Plantae), and the greenish tinge in the animal’s hair is a luxuriant growth of photosynthetic prokaryotes (domain Bacteria). This photograph exemplifies a theme reflected in our book’s title: connections between living things. The sloth depends on trees for food and shelter; the tree uses nutrients from the decomposition of the sloth’s feces; the prokaryotes gain access to the sunlight necessary for photosynthesis by living on the sloth; and the sloth is camouflaged from predators by its green coat. The diversity of life and its interconnectedness are evident almost everywhere. Earlier we looked at life’s unity in its shared properties, two basic types of cell structure, and common genetic code. And now we have briefly surveyed its diversity. In the next module, we explore how evolution explains both the unity and the diversity of life.

Protists (multiple kingdoms)

Kingdom Plantae

Kingdom Fungi

Kingdom Animalia

 Figure 1.6 The three domains of life Evolution, the Core Theme of Biology

7

1.7 Evolution explains the unity and diversity of life The history of life, as documented by fossils, is a saga of a changing Earth billions of years old, inhabited by an evolving cast of living forms (Figure 1.7A). And yet, there is relatedness among these diverse forms, and patterns of ancestry can be traced through the fossil record and other evidence. Evolution accounts for life’s dual nature of kinship and diversity. In November 1859, the English naturalist Charles Darwin (Figure 1.7B) published one of the most important and influential books ever written. Entitled On the Origin of Species by Means of Natural Selection, Darwin’s book was an immediate bestseller and soon made his name almost synonymous with the concept of evolution. Darwin stands out in history with people like Newton and Einstein, scientists who synthesized comprehensive theories with great explanatory power. The Origin of Species articulated two main points. First, Darwin presented a large amount of evidence to support the idea of evolution—that species living today are descendants of ancestral species. Darwin called his evolutionary theory “descent with modification.” It was an insightful phrase, as it captured both the unity of life (descent from a common ancestor) and the diversity of life (modification as species diverged from their ancestors). Darwin’s second point was to propose a mechanism for evolution, which he called natural selection. Darwin synthesized this idea from observations that by themselves were neither profound nor original. Others had the pieces of the puzzle, but Darwin saw how they fit together. He started with the following two observations: (1) Individuals in a population vary in their traits, many of which are passed on from parents to offspring. (2) A population can produce far more offspring than the environment can support. From these two observations, Darwin inferred that those individuals with heritable traits best suited to the environment are more likely to survive and reproduce than are less well-suited individuals. As a result of this unequal reproductive success over many generations, a higher and higher proportion of individuals will have the advantageous traits. The result of natural selection is evolutionary adaptation, the accumulation of favorable traits in a population over time. Figure 1.7C uses a simple example to show how natural selection works. ��� An imaginary beetle population has colonized

an area where the soil has been blackened by a recent brush fire. Initially, the population varies extensively in the inherited coloration of individuals, from very light gray to charcoal. ��� A bird eats the beetles it sees most easily, the light-colored ones. This selective predation reduces the number of light-colored beetles and favors the survival and reproductive success of the darker  Figure 1.7B beetles. ��� The surviving beetles Charles Darwin in 1859 reproduce. After several generations, the population is quite different from the original one. As a result of natural selection, the frequencies of the darker-colored beetles in the population have increased. Darwin realized that numerous small changes in populations caused by natural selection could eventually lead to major alterations of species. He proposed that new species could evolve as a result of the gradual accumulation of changes over long periods of time. (We’ll explore evolution and natural selection in more detail in Chapters 13 and 14.) We see the exquisite results of natural selection in every kind of organism. Each species has its own set of evolutionary adaptations that have evolved over time. Consider the two very

��� Population with varied inherited traits

��� Elimination of individuals with certain traits

 Figure 1.7A Fossil of Dimetrodon. This 3-m-long carnivore was more closely related to mammals than to reptiles.

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��� Reproduction of survivors  Figure 1.7C An example of natural selection in action

Ground pangolin

Killer whale

different mammals shown in Figure 1.7D. The ground pangolin, found in southern and eastern Africa, has a tough body armor of overlapping scales, protecting it from most predators. The pangolin uses its unusually long tongue to prod ants out of their nests. The killer whale is a mammal adapted for life at sea. It breathes air through nostrils on the top of its head and communicates with its companions by emitting clicking sounds that carry in water. Killer whales use sound echoes to detect schools of fish or other prey. The pangolin’s armor and the killer whale’s echolocating ability arose over many, many generations as individuals with heritable traits that made them better adapted to the environment had greater reproductive success. Evolution— descent with modification—explains both how these two mammals are related and how they differ. Evolution is the core theme that makes sense of everything we know and learn about life.

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● On average, those individuals with heritable traits best suited to the local environment produce the greatest number of offspring. This unequal reproductive success increases the frequency of those traits in the population.

 Figure 1.7D Examples of adaptations to different environments

How does natural selection adapt a population of organisms to its environment?

The Process of Science 1.8 Scientific inquiry is used to ask and answer questions about nature if the premises are true. If all organisms are made of cells (premise 1), and humans are organisms (premise 2), then humans are composed of cells (deduction). This deduction is a prediction that can be tested by examining human tissues.

Theories in Science How is a theory different from a hypothesis? A scientific theory is much broader in scope than a hypothesis. It is usually general enough to generate many new, specific hy Figure 1.8 Alison Jolly potheses that can then be tested. with her research subjects, And a theory is supported by a ring-tailed lemurs large and usually growing body of evidence. Theories that become widely adopted (such as the theory of evolution) explain a great diversity of observations and are supported by a vast accumulation of evidence.

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Contrast inductive reasoning with deductive reasoning. ● Inductive reasoning derives a generalization from many observations; deductive reasoning predicts specific outcomes from a general premise.

The word science is derived from a Latin verb meaning “to know.” Science is a way of knowing—an approach to understanding the natural world. It stems from our curiosity about ourselves and the world around us. And it involves the process of inquiry—a search for information, explanations, and answers to specific questions. Scientific inquiry involves making observations, forming hypotheses, and testing predictions. Recorded observations and measurements are the data of science. Some data are quantitative, such as numerical measurements. Other data may be descriptive, or qualitative. For example, primatologist Alison Jolly has spent over 40 years making observations of lemur behavior during field research in Madagascar, amassing data that is mostly qualitative (Figure 1.8). Collecting and analyzing observations can lead to conclusions based on a type of logic called inductive reasoning. This kind of reasoning derives generalizations from a large number of specific observations. “All organisms are made of cells” is an inductive conclusion based on the discovery of cells in every biological specimen observed over two centuries of time. Careful observations and the inductive conclusions they lead to are fundamental to understanding nature. Observations often stimulate us to seek natural causes and explanations. Such inquiry usually involves the forming and testing of hypotheses. A hypothesis is a proposed explanation for a set of observations. A good hypothesis leads to predictions that scientists can test by recording additional observations or by designing experiments. Deduction is the type of logic used to come up with ways to test hypotheses. In deductive reasoning, the logic flows from general premises to the specific results we should expect

The Process of Science

9

1.9 Scientists form and test hypotheses and share their results Let’s explore the elements of scientific inquiry with two case studies, one from everyday life and one from a research project.

A Case Study from Everyday Life We all use hypotheses in solving everyday problems. Let’s say, for example, that your flashlight fails during a campout. That’s an observation. The question is obvious: Why doesn’t the flashlight work? Two reasonable hypotheses based on past experience are that either the batteries in the flashlight are dead or the bulb is burned out. Each of these hypotheses leads to predictions you can test with experiments or further observations. For example, the dead-battery hypothesis predicts that replacing the batteries with new ones will fix the problem. Figure 1.9A diagrams this campground inquiry.

Observation

Question

Hypothesis #1: Dead batteries

Hypothesis #2: Burned-out bulb

Prediction: Replacing batteries will fix problem.

Prediction: Replacing bulb will fix problem.

Experiment:

Experiment:

Test prediction by replacing batteries.

Test prediction by replacing bulb.

Test falsifies hypothesis. Revise hypothesis or pose new one.

Test does not falsify hypothesis. Make additional predictions and test them.

 Figure 1.9A An example of hypothesis-based science

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The flashlight example illustrates two important points. First, a hypothesis must be testable—there must be some way to check its validity. Second, a hypothesis must be falsifiable— there must be some observation or experiment that could show that it is not true. As shown on the left in Figure 1.9A, the hypothesis that dead batteries are the sole cause of the problem was falsified by replacing the batteries with new ones. As shown on the right, the burned-out-bulb hypothesis is the more likely explanation. Notice that testing supports a hypothesis not by proving that it is correct but by not eliminating it through falsification. Perhaps the bulb was simply loose and the new bulb was inserted correctly. Testing cannot prove a hypothesis beyond a shadow of doubt, because it is impossible to exhaust all alternative hypotheses. A hypothesis gains credibility by surviving multiple attempts to falsify it, while alternative hypotheses are eliminated by testing.

A Case Study from Science To learn more about how science works, let’s examine some actual scientific research. The story begins with a set of observations and generalizations. Many poisonous animals are brightly colored, often with distinctive patterns. This so-called warning coloration apparently says “dangerous species” to potential predators. But there are also mimics. These imposters resemble poisonous species but are actually harmless. A question that follows from these observations is: What is the function of mimicry? A reasonable hypothesis is that mimicry is an evolutionary adaptation that reduces the harmless animal’s risk of being eaten. In 2001, biologists David and Karin Pfennig, along with William Harcombe, one of their undergraduate students, designed an elegant set of field experiments to test the hypothesis that mimics benefit because predators confuse them with the harmful species. A venomous snake called the eastern coral snake has warning coloration: bold, alternating rings of red, yellow, and black (Figure 1.9B, on the facing page). (A venomous species delivers its poison by stinging, stabbing, or biting.) Predators rarely attack these snakes. The predators do not learn this avoidance behavior by trial and error; a first encounter with a coral snake would usually be deadly. Natural selection has apparently increased the frequency of predators that inherit an instinctive avoidance of the coral snake’s coloration. The nonvenomous scarlet king snake mimics the ringed coloration of the coral snake (Figure 1.9C). Both types of snakes live in North and South Carolina, but king snakes are also found in regions that have no coral snakes. The geographic distribution of these snakes made it possible for the researchers to test a key prediction of the mimicry hypothesis: Mimicry should help protect king snakes from predators, but only in regions where coral snakes also live. Avoiding snakes with warning coloration is an adaptation of predator populations that evolved in areas where coral snakes are present. Therefore, predators adapted to the warning coloration of coral snakes will attack king snakes less frequently than will predators in areas where coral snakes are absent.

(the artificial brown snakes). Ideally, the experimental and control groups differ only in the one factor the experiment is designed to test—in our example, the effect of the snakes’ coloration on the behavior of predators. Without the control group, the researchers would not have been able to rule out other variables, such as the number of predators in the different test areas. The experimental design left coloration as the only factor that could account for the low predation rate on the artificial king snakes placed within the range of coral snakes.

The Culture of Science Science is a so-

Eastern coral snake (venomous)

To test this prediction, Harcombe made hundreds of artificial snakes out  Figure 1.9C Scarlet of wire covered with a claylike subking snake (nonvenstance called plasticine. He made two omous) versions of fake snakes: an experimental group with the color pattern of king snakes and a control group of plain brown snakes as a basis of comparison. The researchers placed equal numbers of the two types of artificial snakes in field sites throughout North and South Carolina, including the region where coral snakes are absent. After four weeks, they retrieved the snakes and recorded how many had been attacked by looking for bite or claw marks. The most common predators were foxes, coyotes, and raccoons, but black bears also attacked some of the snakes (Figure 1.9D). The data fit the key prediction of the mimicry hypothesis. The artificial king snakes were attacked less frequently than the artificial brown snakes only in field sites within the geographic range of the venomous coral snakes. The bar graph in Figure 1.9E summarizes the results. This case study is an example of a controlled experiment, one that is designed to compare an experimental group (the artificial king snakes, in this case) with a control group

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Why is it difficult to draw a conclusion from an experiment that does not include a control group?

● Without a control group, you don’t know if the experimental outcome is due to the variable you are trying to test or to some other variable.

 Figure 1.9B

cial activity, with most scientists working in teams, which often include graduate and undergraduate students. Scientists share information through publications, seminars, meetings, and personal communication. The Internet has added a new medium for this exchange of ideas and data. Scientists build on what has been learned from earlier research and often check each other’s claims by attempting to confirm observations or repeat experiments. Science seeks natural causes for natural phenomena. Thus, the scope of science is limited to the study of structures and processes that we can directly observe and measure. Science can neither support nor falsify hypotheses about supernatural forces or explanations, for such questions are outside the bounds of science. The process of science is necessarily repetitive: In testing a hypothesis, researchers may make observations that call for rejection of the hypothesis or at least revision and further testing. This process allows biologists to circle closer and closer to their best estimation of how nature works. As in all quests, science includes elements of challenge, adventure, and luck, along with careful planning, reasoning, creativity, cooperation, competition, patience, and persistence.

100 Percent of total attacks on artificial snakes

Artificial king snakes

84%

83% 80

Artificial brown snakes 60 40 20

17%

16%

 Figure 1.9D Artificial king snake that was not attacked (above); artificial brown snake that was attacked by a bear (right)

0 Coral snakes absent

Coral snakes present

 Figure 1.9E Results of mimicry experiment The Process of Science

11

Biology and Everyday Life 1.10 Biology, technology, and society are connected in important ways

Many issues facing society are related to biology (Figure 1.10). Most of these issues also involve our expanding technology. Science and technology are interdependent, but their basic goals differ. The goal of science is to understand natural phenomena. In contrast, the goal of technology is to apply scientific knowledge for some specific purpose. Scientists often speak of “discoveries,” while engineers more often speak of “inventions.” The beneficiaries of those inventions also include scientists, who use new technology in their research. And scientific discoveries often lead to the development of new technologies. Technology depends less on the curiosity that drives basic science than on the needs and wants of people and on the social environment of the times. Debates about technology center more on “should we do it” than “can we do it.” Should insurance companies have access to individuals’ DNA information? Should we permit research with embryonic stem cells? Technology has improved our standard of living in many ways, but not without adverse consequences. Technology that keeps people healthier has enabled Earth’s population to grow 10-fold in the past three centuries and to more than double to 6.8 billion in just the past 40 years. The environmental effects of this growth can be devastating. Global climate change, toxic wastes, deforestation, nuclear accidents, and extinction of species are just some of the repercussions

CHAPTER 1

How do science and technology interact?

1.11 Evolution is connected to our everyday lives

Evolution is the core theme of biology. To emphasize the centrality of evolution to biology, we include an Evolution Connection module in each chapter in this book. But is evolution connected to your everyday life? And if so, in what ways? Biologists now recognize that differences in DNA among individuals, populations, and species reflect the patterns of evolutionary change. The new technology of automatic DNAsequencing machines has enabled scientists to determine the order of the billions of DNA bases in the human genome and in the genomes of other species. Comparisons of those sequences allow us to identify genes shared across many species, study the actions of such genes in other species, and, in some cases, search for new medical treatments. Identifying beneficial genes in relatives of our crop plants has permitted the breeding or genetic engineering of enhanced crops. The recognition that DNA differs between people has led to the use of DNA tests to identify individuals. DNA profiling is now used to help convict or exonerate the accused, determine paternity, and identify remains. Evolution teaches us that the environment is a powerful selective force for traits that best adapt populations to their environment. We are major agents of environmental change when we take drugs to combat infection or grow crops in 12

?

Biology: Exploring Life

pesticide-dependent monocultures or alter Earth’s habitats. We have seen the effects of such environmental changes in antibiotic-resistant bacteria, pesticide-resistant pests, endangered species, and increasing rates of extinction. How can evolutionary theory help? It can help us be more judicious in our use of antibiotics and pesticides and help us develop strategies for conservation efforts. It can help us create flu vaccines and HIV drugs by tracking the rapid evolution of these viruses. It can identify new sources of drugs. For example, by tracing the evolutionary history of the endangered Pacific Yew tree, once the only source of the cancer drug Taxol, scientists have discovered similar compounds in more common trees. We hope this book will help you develop an appreciation for evolution and biology and help you apply your new knowledge to evaluating issues ranging from your personal health to the well-being of the whole world. Biology offers us a deeper understanding of ourselves and our planet and a chance to more fully appreciate life in all of its diversity.

?

How might an understanding of evolution contribute to the development of new drugs?

● As one example, we can find organisms that share our genes and similar cellular processes and test the actions of potential drugs in these organisms.

EVOLUTION CONNECTION

of more and more people wielding more and more technology. Science can help us identify such problems and provide insight into what course of action may prevent further damage. But solutions to these problems have as much to do with politics, economics, and cultural values as with science and technology. Now that science and technology have become such powerful aspects of society, every citizen has a responsibility to  Figure 1.10 Biology and develop a reasonable amount technology in the news of scientific literacy. The crucial science-technologysociety relationship is a theme that adds to the significance of any biology course.

● New scientific discoveries may lead to new technologies; new technologies may increase the ability of scientists to search for new knowledge.

CONNECTION

C H A P T E R

1

R E V I E W

For Practice Quizzes, BioFlix, MP3 Tutors, and Activities, go to www.masteringbiology.com.

The Process of Science (1.8–1.9) Scientific inquiry is used to ask and answer questions about nature. Scientists use inductive reasoning to draw general conclu-

1.8

Reviewing the Concepts Themes in the Study of Biology (1.1–1.4) All forms of life share common properties. Biology is the scientific study of life. Properties of life include order, reproduction, growth and development, energy processing, response to the environment, regulation, and evolutionary adaptation.

1.1

In life’s hierarchy of organization, new properties emerge at each level. Biological organization unfolds as follows: biosphere >

1.2

ecosystem > community > population > organism > organ system > organ > tissue > cell > organelle > molecule. Emergent properties result from the interactions among component parts. 1.3 Cells are the structural and functional units of life. Eukaryotic cells contain membrane-enclosed organelles, including a nucleus containing DNA. Prokaryotic cells are smaller and lack such organelles. Structure is related to function at all levels of biological organization. Systems biology models the complex interactions of biological systems, such as the molecular interactions within a cell. Organisms interact with their environment, exchanging matter and energy. Ecosystems are

1.4

characterized by the cycling of chemical nutrients from the atmosphere O and soil through proSunlight ducers, consumers, Producers (such as plants) decomposers, and back to the environCO ment. Energy flows one way through an Water and minerals taken up by tree roots ecosystem—entering as sunlight, converted to chemical energy by producers, passed on to consumers, and exiting as heat. 2

O2 Heat

Consumers (such as animals)

sions from many observations. They form hypotheses and use deductive reasoning to make predictions. Data may be qualitative or quantitative. A scientific theory is broad in scope, generates new hypotheses, and is supported by a large body of evidence. 1.9

Scientists form and test hypotheses and share their results.

Predictions can be tested with experiments, and results can either falsify or support the hypothesis. In a controlled experiment, the use of control and experimental groups helps to demonstrate the effect of a single variable. Science is a social process: scientists share information and review each other's results.

Biology and Everyday Life (1.10–1.11) Biology, technology, and society are connected in important ways. Technological advances stem from scientific research, and

1.10

research benefits from new technologies. Evolution is connected to our everyday lives. Evolutionary theory is useful in medicine, agriculture, forensics, and conservation. Human-caused environmental changes are powerful selective forces that affect the evolution of many species. 1.11

Connecting the Concepts 1. Biology can be described as having both a vertical scale and a horizontal scale. Explain what that means. 2. Complete the following map organizing some of biology’s major concepts.

Chemical energy (food)

2

CO2

Biology Cycling of chemical nutrients

Decomposers (in soil)

is the study of

(a)

Evolution, the Core Theme of Biology (1.5–1.7)

has changed through the process of

The unity of life is based on DNA and a common genetic code. DNA is responsible for heredity and for pro-

1.5

(b)

gramming the activities of a cell. A species’ genes are coded in the sequences of the four building blocks making up DNA’s double helix. 1.6 The diversity of life can be arranged into three domains. Taxonomy names species and classifies

mechanism is depends on accounts for

(c)

them into a system of broader groups. Domains Bacteria and Archaea consist of prokaryotes. The eukaryotic domain, Eukarya, includes various protists and the kingdoms Fungi, Plantae, and Animalia. 1.7 Evolution explains the unity and diversity of life. Darwin synthesized the theory of evolution by natural selection. Observations

Inferences

Heritable variations

Natural selection: Unequal reproductive success leads to evolution of adaptations in populations.

leads to

codes for

accounts for is evidence of

(d)

diversity of life seen in

(e)

Overproduction of offspring

DNA (genetic code)

seen in variations in

cells as basic units of life

seen in

common properties of living organisms

Chapter 1 Review

13

Testing Your Knowledge

Describing, Comparing, and Explaining

Multiple Choice

10. In an ecosystem, how is the movement of energy similar to that of chemical nutrients, and how is it different?

4. Single-celled amoebas and bacteria are grouped into different domains because a. amoebas eat bacteria. b. bacteria are not made of cells. c. bacterial cells lack a membrane-enclosed nucleus. d. bacteria decompose amoebas. e. amoebas are motile; bacteria are not. 5. A biologist studying interactions among the protists in an ecosystem could not be working at which level in life’s hierarchy? (Choose carefully and explain your answer.) a. the population level b. the molecular level c. the community level d. the organism level e. the organ level 6. Which of the following questions is outside the realm of science? a. Which organisms play the most important role in energy input to a forest? b. What percentage of music majors take a biology course? c. What is the physical nature of the universe? d. What is the influence of the supernatural on current events? e. What is the dominance hierarchy in a troop of ring-tailed lemurs? 7. Which of the following statements best distinguishes hypotheses from theories in science? a. Theories are hypotheses that have been proved. b. Hypotheses are tentative guesses; theories are correct answers to questions about nature. c. Hypotheses usually are narrow in scope; theories have broad explanatory power. d. Hypotheses and theories are different terms for essentially the same thing in science. e. Theories cannot be falsified; hypotheses can be falsified. 8. Which of the following best demonstrates the unity among all living organisms? a. descent with modification b. related DNA sequences and common genetic code c. emergent properties d. natural selection e. the three domains 9. The core idea that makes sense of all of biology is a. the process of science. b. the correlation of function with structure. c. systems biology. d. evolution. e. the emergence of life at the level of the cell.

14

CHAPTER 1

Biology: Exploring Life

11. Explain the role of heritable variations in Darwin’s theory of natural selection. 12. Explain what is meant by this statement: The scientific process is not a rigid method. 13. Contrast technology with science. Give an example of each to illustrate the difference. 14. Explain what is meant by this statement: Natural selection is an editing mechanism rather than a creative process.

Applying the Concepts 15. The graph below shows the results of an experiment in which mice learned to run through a maze. 25 Average time to complete maze (min)

3. Which of the following best describes the logic of the scientific process? a. If I generate a testable hypothesis, tests and observations will support it. b. If my prediction is correct, it will lead to a testable hypothesis. c. If my observations are accurate, they will not falsify my hypothesis. d. If my hypothesis is correct, I can make predictions and my results will not falsify my hypothesis. e. If my predictions are good and my tests are right, they will prove my hypothesis.

20 15 10

No reward Food reward

5 0 0

1

2

3 Day

4

5

6

a. State the hypothesis and prediction that you think this experiment tested. b. Which was the control group and which the experimental? Why was a control group needed? c. List some variables that must have been controlled so as not to affect the results. d. Do the data support the hypothesis? Explain. 16. In an experiment similar to the mimicry experiment described in Module 1.9, a researcher counted more predator attacks on artificial king snakes in areas with coral snakes than in areas outside the range of coral snakes. From those numbers, the researcher concluded that the mimicry hypothesis is false. Do you think this conclusion is justified? Why or why not? 17. The fruits of wild species of tomato are tiny compared to the giant beefsteak tomatoes available today. This difference in fruit size is almost entirely due to the larger number of cells in the domesticated fruits. Plant biologists have recently discovered genes that are responsible for controlling cell division in tomatoes. Why would such a discovery be important to producers of other kinds of fruits and vegetables? To the study of human development and disease? To our basic understanding of biology? 18. The news media and popular magazines frequently report stories that are connected to biology. In the next 24 hours, record the ones you hear or read about in three different sources and briefly describe the biological connections in each story. Answers to all questions can be found in Appendix 4.

U N I T

I

The Life of the Cell

2

The Chemical Basis of Life

3

The Molecules of Cells

4

A Tour of the Cell

5

The Working Cell

6

How Cells Harvest Chemical Energy

7

Photosynthesis: Using Light to Make Food 15

C H A P T E R

The Chemical Basis of Life

2 BIG IDEAS





 

O

Elements, Atoms, and Compounds

H

(2.1–2.4)

Chemical Bonds

Living organisms are made of atoms of certain elements, mostly combined into compounds.

ⴚ

ⴙ ⴚ

ⴚ ⴙ ⴚ

(2.5–2.9)

The structure of an atom determines what types of bonds it can form with other atoms.

Na⫹

Cl⫺

ⴙ ⴚ ⴙ ⴚ

ⴚ ⴙ Cl⫺

Na⫹

ⴙ

ⴚ ⴙ

ⴙ

ⴚ

Water’s LifeSupporting Properties (2.10–2.16)

The unique properties of water derive from the polarity of water molecules.

16

H

iology is about life, but it is also about chemistry. Chemicals are the very stuff making up our bodies, those of other organisms, and the physical environment around us. Your cells, tissues, and organs are all made of chemical compounds. And the activities of your body—from reading these words to running a race—are all based on chemical reactions. So understanding and appreciating life begins with a basic understanding of chemistry: the elements that make up living matter and the ways in which the atoms of those elements interact. Life’s chemistry is tied to water. The chemical reactions of your body take place in cells whose water content ranges from 70% to 95%. As you can see in this satellite photograph of our planet, three-quarters of Earth’s surface is covered by water. Life began in water and evolved there for 3 billion years before

B

spreading onto land. And modern life, even land-dwelling life, is still dependent on water. All living organisms require water more than any other substance. What properties of the simple water molecule make it so indispensable to life on Earth? You’ll find out in this chapter. This chapter will also make connections to the themes introduced in Chapter 1. One of these themes is the organization of life into a hierarchy of structural levels, with new properties emerging at each successive level. Emergent properties are apparent even at the lowest levels of biological organization— the ordering of atoms into molecules and the interactions of those molecules. The intricate structures and complex functions of all living organisms arise from these interactions. We begin our story of biology with the basic concepts of chemistry that will apply throughout our study of life. 17

Elements, Atoms, and Compounds 2.1 Organisms are composed of elements, in combinations called compounds

TABLE 2.1 Element

E L E M E N T S I N T H E H U M A N B O DY

Symbol

Oxygen

O

65.0%

Carbon

C

18.5%

Hydrogen

H

9.5%

Nitrogen

N

3.3%

Calcium

Ca

1.5%

Phosphorus

P

1.0%

Potassium

K

0.4%

Sulfur

S

0.3%

Sodium

Na

0.2%

Chlorine

Cl

0.2%

Magnesium

Mg

0.1%

Chlorine

CHAPTER 2

The Chemical Basis of Life

3.7%

chromium (Cr), cobalt (Co), copper (Cu), fluorine (F), iodine (I), iron (Fe), manganese (Mn), molybdenum (Mo), selenium (Se), silicon (Si), tin (Sn), vanadium (V), zinc (Zn)

elements are the main ingredients of biological molecules such as proteins, sugars, and fats. Calcium (Ca), phosphorus (P), potassium (K), sulfur, sodium, chlorine, and magnesium (Mg) account for most of the remaining 4% of the human body. These elements are involved in such important functions as bone formation (calcium and phosphorus) and nerve signaling (potassium, sodium, calcium, and chlorine). The trace elements listed at the bottom of the table are essential, but only in minute quantities. We explore the importance of trace elements to your health next.

?

Explain how table salt illustrates the theme of emergent properties.

Sodium chloride

 Figure 2.1 The emergent properties of the edible compound sodium chloride

18

96.3%

Trace elements, less than 0.01% of human body weight: Boron (B),



Sodium

Percentage of Body Weight (Including Water)

● The elements that make up the edible crystals of table salt, sodium and chlorine, are in pure form a metal and a poisonous gas.

Living organisms and everything around them are composed of matter, which is defined as anything that occupies space and has mass. (In everyday language, we can think of mass as an object’s weight.) Matter is found on Earth in three physical states: solid, liquid, and gas. Types of matter as diverse as rocks, water, air, and biology students are all composed of chemical elements. An element is a substance that cannot be broken down to other substances by ordinary chemical means. Today, chemists recognize 92 elements that occur in nature; gold, copper, carbon, and oxygen are some examples. Chemists have also made a few dozen synthetic elements. Each element has a symbol, the first letter or two of its English, Latin, or German name. For instance, the symbol for sodium, Na, is from the Latin word natrium; the symbol O comes from the English word oxygen. A compound is a substance consisting of two or more different elements combined in a fixed ratio. Compounds are much more common than pure elements. In fact, few elements exist in a pure state in nature. Many compounds consist of only two elements; for instance, table salt (sodium chloride, NaCl) has equal parts of the elements sodium (Na) and chlorine (Cl). Pure sodium is a metal and pure chlorine is a poisonous gas. Chemically combined, however, they form an edible compound (Figure 2.1). The elements hydrogen (H) and oxygen (O) exist as gases. Combined in a ratio of 2:1, they form the most abundant compound on Earth—water (H2O). These are simple examples of organized matter having emergent properties: A compound has characteristics different from those of its elements. Most of the compounds in living organisms contain at least three or four elements. Sugar, for example, is formed of carbon (C), hydrogen, and oxygen. Proteins are compounds containing carbon, hydrogen, oxygen, nitrogen (N), and a small amount of sulfur (S). Different arrangements of the atoms of these elements give rise to the unique properties of each compound. About 25 elements are essential to life. As you can see in Table 2.1, four of these—oxygen, carbon, hydrogen, and nitrogen—make up about 96% of the weight of the human body, as well as that of most other living organisms. These four

2.2 Trace elements are common additives to food and water

Some trace elements, such as iron (Fe), are needed by all forms of life. Iron makes up only about 0.004% of your body weight but is vital for energy processing and for transporting oxygen in your blood. Other trace elements, such as iodine (I), are required only by certain species. You need to ingest only a tiny amount of iodine each day, about 0.15 milligram (mg). Iodine is an essential ingredient of a hormone produced by the thyroid gland, which is located in the neck. An iodine deficiency in the diet causes the thyroid gland to grow to abnormal size, a condition called goiter (Figure 2.2A). Iodine deficiency is also linked to mental retardation. Adding iodine to table salt has reduced the incidence of iodine deficiency in many countries. Unfortu Figure 2.2A Goiter, a nately, iodized salt is not availsymptom of iodine deficiency, able everywhere, and an in a Burmese woman estimated 2 billion people worldwide have insufficient iodine intake. Seafood, kelp, strawberries, and dark, leafy greens are good natural sources. Thus, deficiencies are often found in inland regions, especially in areas where the soil is lacking in iodine. Although most common in developing nations, iodine deficiencies may also result from excessive consumption of highly processed foods (which often use non-iodized salt) and low-salt diets intended to lower the risk of cardiovascular disease. Iodine is just one example of a trace element added to food or water to improve health. For more than 50 years, the American Dental Association has supported fluoridation of community drinking water as a public health measure. Fluoride is a form of fluorine (F), an element in Earth’s crust that is found in small amounts in all water sources. In many areas, fluoride is added during the municipal water treatment process to raise levels to a concentration that can reduce tooth decay. If you mostly drink bottled water, your fluoride intake may be reduced, although some bottled water now contains added fluoride. Fluoride is also frequently added to dental products, such as toothpaste and mouthwash (Figure 2.2B). Chemicals are added to food to help preserve it, make it more nutritious, or simply make it look better. Look at the nutrition facts label from the side of the cereal box in Figure 2.2C to see a familiar example of how foods are fortified with mineral elements. Iron, for example, is a trace element commonly added to foods. (You can actually see that iron has been added to a fortified cereal by crushing the cereal and then stirring a magnet through it.) Also note that the nutrition facts label lists numerous vitamins that are added to improve the nutritional value of the cereal. For instance, the cereal in this example supplies 10% of the

 Figure 2.2B Mouthwash and toothpaste with added fluoride

recommended daily value for vitamin A. Vitamins consist of more than one element and are examples of compounds. In the next module, we explore the structure of an atom and how this structure determines the chemical properties of elements.

?

In addition to iron, what other trace elements are found in the cereal in Figure 2.2C? Does Total provide the “total” amount needed of these elements?

● Zinc and copper: Total provides 100% of the zinc but only 4% of the copper needed in a day.

CONNECTION

 Figure 2.2C Nutrition facts from a fortified cereal

Elements, Atoms, and Compounds

19

2.3 Atoms consist of protons, neutrons, and electrons Each element consists of one kind of atom, which is different from the atoms of other elements. An atom, named from a Greek word meaning “indivisible,” is the smallest unit of matter that still retains the properties of an element. Atoms are so small that it would take about a million of them to stretch across the period printed at the end of this sentence.

TABLE 2.3

ISOTOPES OF CARBON Carbon-12

Protons

6

Neutrons 6

Mass number 12

Electrons 6

Carbon-13 6 7 6

Mass number 13

Carbon-14 6 8

Mass number 14

6

Subatomic Particles Physicists have split the atom into

Atomic Number and Atomic Mass All atoms of a particular element have the same unique number of protons. This number is the element’s atomic number. Thus, an atom of helium, with 2 protons, has an atomic number of 2. Carbon, with 6 protons, has an atomic number of 6 (Figure 2.3B). Note that in these atoms, the atomic number is also the number of Carbon

Helium

Electron cloud

Nucleus 



2e









Electron cloud 2



2 2

Protons Neutrons



Mass number  4

Electrons

Nucleus 6



6 6

Protons Neutrons



electrons. Unless otherwise indicated, an atom has an equal number of protons and electrons, and thus its net electrical charge is 0 (zero). An atom’s mass number is the sum of the number of protons and neutrons in its nucleus. For helium, the mass number is 4; for carbon, it is 12 (Figures 2.3A and 2.3B). The mass of a proton and the mass of a neutron are almost identical and are expressed in a unit of measurement called the dalton. Protons and neutrons each have masses close to 1 dalton. An electron has only about 1/2,000 the mass of a proton, so it contributes very little to an atom’s mass. Thus, an atom’s atomic mass (or weight) is approximately equal to its mass number—the sum of its protons and neutrons.

Isotopes All atoms of an element have the same atomic number, but some atoms of that element may differ in mass number. The different isotopes of an element have the same number of protons and behave identically in chemical reactions, but they have different numbers of neutrons. Table 2.3 shows the numbers of subatomic particles in the three isotopes of carbon. Carbon-12 (also written 12C), with 6 neutrons, accounts for about 99% of the carbon in nature. Most of the remaining 1% consists of carbon-13 (13C), with 7 neutrons. A third isotope, carbon-14 (14C), with 8 neutrons, occurs in minute quantities. Notice that all three isotopes have 6 protons—otherwise, they would not be carbon. Both 12C and 13C are stable isotopes, meaning their nuclei remain intact more or less forever. The isotope 14 C, on the other hand, is unstable, or radioactive. A radioactive isotope is one in which the nucleus decays spontaneously, giving off particles and energy. Radiation from decaying iso6e topes can damage cellular molecules and thus can pose serious risks to living organisms. But  radioactive isotopes can be helpful, as in their  use in dating fossils (see Module 15.5). They are also used in biological research and medicine, as we see next. Mass number  12

Electrons

 Figure 2.3A Two models of a helium atom  Figure 2.3B Model of a carbon atom

20

CHAPTER 2

The Chemical Basis of Life

?

A nitrogen atom has 7 protons, and its most common isotope has 7 neutrons. A radioactive isotope of nitrogen has 9 neutrons. What is the atomic number and mass number of this radioactive nitrogen? ● Atomic number = 7; mass number = 16

more than a hundred types of subatomic particles. However, only three kinds of particles are relevant here. A proton is a subatomic particle with a single positive electrical charge (). An electron is a subatomic particle with a single negative charge (). A neutron, as its name implies, is electrically neutral (has no charge). Figure 2.3A shows two very simple models of an atom of the element helium (He), the “lighter-than-air” gas that makes balloons rise. Notice that two protons (  ) and two neutrons ( ) are tightly packed in the atom’s central core, or nucleus. Two electrons () move around the nucleus at nearly the speed of light. The attraction between the negatively charged electrons and the positively charged protons holds the electrons near the nucleus. The left-hand model shows the number of electrons in the atom. The right-hand model, slightly more realistic, shows a spherical cloud of negative charge created by the rapidly moving electrons. Neither model is drawn to scale. In real atoms, the electrons are very much smaller than the protons and neutrons, and the electron cloud is much bigger compared to the nucleus. Imagine that this atom was the size of a baseball stadium: The nucleus would be the size of a fly in center field, and the electrons would be like two tiny gnats buzzing around the stadium.

CONNECTION

2.4 Radioactive isotopes can help or harm us

Living cells cannot distinguish between isotopes of the same element. Consequently, organisms take up and use compounds containing radioactive isotopes in the usual way. Because radioactivity is easily detected by instruments, radioactive isotopes are useful as tracers—biological spies, in effect—for monitoring the fate of atoms in living organisms.

Basic Research Biologists often use radioactive tracers to follow molecules as they undergo chemical changes in an organism. For example, researchers have used carbon dioxide (CO2) containing the radioactive isotope 14C to study photosynthesis. Using sunlight to power the conversion, plants take in CO2 from the air and use it to make sugar molecules. Radioactively labeled CO2 has enabled researchers to trace the sequence of molecules made by plants in the chemical route from CO2 to sugar.

Healthy person

Alzheimer’s patient

 Figure 2.4B PET images of brains of a healthy person (left) and a person with Alzheimer’s disease (right). Red and yellow colors indicate high levels of PIB bound to beta-amyloid plaques.

Medical Diagnosis and Treatment

called beta-amyloid. Researchers have identified a protein molecule called PIB that binds to beta-amyloid. PIB contains a radioactive isotope that can be detected on a PET scan. Figure 2.4B shows PET images of the brains of a healthy person (left) and a person with Alzheimer’s (right) injected with PIB. Notice that the brain of the Alzheimer’s patient has high levels of PIB (red and yellow areas), whereas the unaffected person’s brain has lower levels (blue). New therapies are focused on limiting the production of beta-amyloid or clearing it from the brain. A diagnostic test using PIB would allow researchers to monitor the effectiveness of new drugs in people living with the disease.

Dangers Although radioactive isotopes have many beneficial uses, uncontrolled exposure to them can harm living organisms by damaging molecules, especially DNA. The particles and energy thrown off by radioactive atoms can break chemical bonds and also cause abnormal bonds to form. The explosion of a nuclear reactor at Chernobyl, Ukraine, in 1986 released large amounts of radioactive isotopes into the environment, which drifted over large areas of Russia, Belarus, and Europe. A few dozen people died from acute radiation poisoning, and over 100,000 people were evacuated from the immediate area. Increased rates of thyroid cancer in children exposed to the radiation have been reported, and many thousands may be at increased risk of future cancers. Natural sources of radiation can also pose a threat. Radon, a radioactive gas, may be a cause of lung cancer. Radon can contaminate buildings in regions where underlying rocks naturally contain uranium, a radioactive element. Homeowners can buy a radon detector or hire a company to test their home to ensure that radon levels are safe. If levels are found to be unsafe, technology exists to remove radon from homes.

?  Figure 2.4A Technician monitoring the output of a PET scanner

Why are radioactive isotopes useful as tracers in research on the chemistry of life? ● Organisms incorporate radioactive isotopes of an element into their molecules, and researchers can use special scanning devices to detect the presence of these isotopes in biological pathways or locations in the body.

Radioactive isotopes may also be used to tag chemicals that accumulate in specific areas of the body, such as phosphorus in bones. After injection of such a tracer, a special camera produces an image of where the radiation collects. In most diagnostic uses, the patient receives only a tiny amount of an isotope. Sometimes radioactive isotopes are used for treatment. As you learned in Module 2.2, the body uses iodine to make a thyroid hormone. Because radioactive iodine accumulates in the thyroid, it can be used to kill cancer cells there. Substances that the body metabolizes such as glucose or oxygen, may also be labeled with a radioactive isotope. Figure 2.4A shows a patient being examined by a PET (positron-emission tomography) scanner, which can produce three-dimensional images of areas of the body with high metabolic activity. PET is useful for diagnosing certain heart disorders and cancers and for basic research on the brain (see Module 28.17). The early detection of Alzheimer’s disease may be a new use for such techniques. This devastating illness gradually destroys a person’s memory and ability to think. As the disease progresses, the brain becomes riddled with deposits (plaques) of a protein

Elements, Atoms, and Compounds

21

Chemical Bonds 2.5 The distribution of electrons determines an atom’s chemical properties atom. Atoms whose outer shells are not full (have unpaired electrons) tend to interact with other atoms—that is, to participate in chemical reactions. Look at the electron shells of the atoms of the four elements that are the main components of biological molecules (highlighted in green in Figure 2.5). Because their outer shells are incomplete all these atoms react readily with other atoms. The hydrogen atom has only 1 electron in its single electron shell, which can accommodate 2 electrons. Atoms of carbon, nitrogen, and oxygen also are reactive because their valence shells, which can hold 8 electrons, are also incomplete. In contrast, the helium atom has a first-level shell that is full with 2 electrons. Neon and argon also have full outer electron shells. As a result, these elements are chemically inert (unreactive). How do chemical interactions between atoms enable them to fill their outer electron shells? When two atoms with incomplete outer shells react, each atom will share, donate, or receive electrons, so that both partners end up with completed outer shells. These interactions usually result in atoms staying close together, held by attractions known as chemical bonds. In the next two modules, we look at two important types of chemical bonds.

?

How many electrons and electron shells does a sodium atom have? How many electrons are in its valence shell? ● 11 electrons; 3 electron shells; 1 electron in the outer shell

To understand how atoms interact with each other—the main subject of this section—we need to explore atomic structure further. Of the three subatomic particles—protons, neutrons, and electrons—only electrons are directly involved in the chemical activity of an atom. Electrons vary in the amount of energy they possess. The farther an electron is from the positively charged nucleus, the greater its energy. Electrons move around the nucleus only at certain energy levels, called electron shells. Depending on an element’s atomic number, an atom may have one, two, or more electron shells surrounding the nucleus. Figure 2.5 is an abbreviated version of the periodic table of the elements (see Appendix 2). It shows the distribution of electrons for the first 18 elements, arranged in rows according to the number of electron shells (one, two, or three). Within each shell, electrons travel in different orbitals, which are discrete volumes of space in which electrons are most likely to be found. Each orbital can hold a maximum of 2 electrons. The first electron shell has only one orbital and can hold only 2 electrons. Thus, hydrogen and helium are the only elements in the first row. For the second and third rows, the outer shell has four orbitals and can hold up to 8 electrons (four pairs). Note that the number of electrons increases by one as you read from left to right across each row in the table and that the electrons don't pair up until all orbitals have at least one electron. It is the number of electrons in the outermost shell, called the valence shell, that determines the chemical properties of an Hydrogen

Helium

First shell

Lithium

Beryllium

Boron

Carbon

Nitrogen

Oxygen

Fluorine

Neon

Sodium

Magnesium

Aluminum

Silicon

Phosphorus

Sulfur

Chlorine

Argon

Second shell

Third shell

 Figure 2.5 The electron distribution diagrams of the first 18 elements in the periodic table

2.6 Covalent bonds join atoms into molecules through electron sharing The strongest kind of chemical bond is the covalent bond, in which two atoms share one or more pairs of outer-shell electrons. Two or more atoms held together by covalent bonds form a molecule. For example, a covalent bond connects two hydrogen atoms in a molecule of the gas H2. 22

CHAPTER 2

The Chemical Basis of Life

Table 2.6, on the next page, shows four ways to represent this molecule. The symbol H2, called the molecular formula, tells you that a hydrogen molecule consists of two atoms of hydrogen. The electron distribution diagram shows that the atoms share two electrons; as a result, both atoms fill their outer (and

attraction for shared electrons is called its electronegativity. The more electronegative an atom, the more strongly it pulls shared Spaceelectrons toward its nucleus. In molecules of Electron Distribution Structural Molecular Filling only one element, such as O2 and H2, the two Diagram Formula Formula Model identical atoms exert an equal pull on the electrons. The bonds in such molecules are said to be H H H2 nonpolar covalent bonds because the electrons H H Hydrogen Single are shared equally between the atoms. Combond pounds such as methane also have nonpolar bonds, because the atoms of carbon and hydrogen are not substantially different in O O O2 O O electronegativity. Double Oxygen In contrast to O2, H2, and CH4, water is combond posed of atoms with different electronegativities. Oxygen is one of the most electronegative of the elements. (Nitrogen is also highly electronegaO H2O tive.) As indicated by the arrows in Figure 2.6, O H H Water oxygen attracts the shared electrons in H2O much more strongly than does hydrogen, so H H that the electrons spend more time near the oxygen atom than near the hydrogen atoms. This unequal sharing of electrons produces a polar covalent bond. In a polar covalent bond, H the pulling of shared, negatively charged H electrons closer to the more electronegative C CH4 H H H C H atom makes that atom partially negative and the Methane other atom partially positive. Thus, in H2O, H the oxygen atom actually has a slight negaH tive charge and each hydrogen atom a slight positive charge. Because of its polar covalent bonds and the wide V shape of the molecule, water is a polar molecule—that is, it has an unequal distribution of charges. It is slightly negative at the oxygen end of the molecule (point of the V) and only) shells. The third column shows a structural formula. slightly positive at each of the two hydrogen ends. The line between the hydrogen atoms represents the single In some cases, two atoms are so unequal in their covalent bond formed by the sharing of a pair of electrons attraction for electrons that the more electronegative atom (1 electron from each atom). A space-filling model, shown in strips an electron completely away from its partner, as we the fourth column, uses color-coded balls to symbolize see next. atoms and comes closest to showing a molecule’s shape. How many covalent bonds can an atom form? It depends ? What is chemically nonsensical about this structure? on the number of additional electrons needed to fill its outer, or valence, shell. This number is called the valence, or bondH C C H ing capacity, of an atom. Looking back at the electron distribution diagrams in Figure 2.5, we see that H can form one bond; O can form two; N, three; and C, four. In an oxygen molecule (O2), shown next in Table 2.6, the two oxygen atoms share two pairs of electrons, forming a (slightly ) double bond. A double bond is indicated by a pair of lines. H2 and O2 are molecules composed of only one element. The third example in the table is a compound. Water (H2O) is a molecule in which two hydrogen atoms are joined to O oxygen by single bonds. And as shown at the bottom of Table 2.6, it takes four hydrogen atoms, each with a valence H H of 1, to satisfy carbon’s valence of 4. This compound, methane (CH4), is a major component of natural gas. (slightly ) (slightly ) Atoms in a molecule are in a constant tug-of-war for the shared electrons of their covalent bonds. An atom’s  Figure 2.6 A water molecule, with polar covalent bonds A LT E R N AT I V E W AY S T O R E P R E S E N T F O U R COMMON MOLECULES

● Each carbon atom has only three covalent bonds instead of the four required by its valence.

TABLE 2.6

Chemical Bonds

23

2.7 Ionic bonds are attractions between ions of opposite charge an ionic bond. The resulting compound, in this case NaCl, is electrically neutral. Sodium chloride is a familiar type of salt, a synonym for an ionic compound. Salts often exist as crystals in nature. Figure 2.7B shows the ions Na+ and Cl– in a crystal of sodium chloride. An NaCl crystal can be of any size (there is no fixed number of ions), but sodium and chloride ions are always present in a 1:1 ratio. The ratio of ions can differ in the various kinds of salts. The environment affects the strength of ionic bonds. In a dry salt crystal, the bonds are so strong that it takes a hammer and chisel to break enough of them to crack the crystal. If the same salt crystal is placed in water, however, the ionic bonds break when the ions interact with water molecules and the salt dissolves, as we’ll discuss in Module 2.13. Most drugs are manufactured as salts because they are quite stable when dry but can dissolve easily in water.

Table salt is an example of how the transfer of electrons can bond atoms together. Figure 2.7A shows how a sodium atom and a chlorine atom can form the compound sodium chloride (NaCl). Notice that sodium has only 1 electron in its outer shell, whereas chlorine has 7. When these atoms interact, the sodium atom donates its single outer electron to chlorine. Sodium now has only two shells, the outer shell having a full set of 8 electrons. When chlorine accepts sodium’s electron, its own outer shell is now full with 8 electrons. Remember that electrons are negatively charged particles. The transfer of an electron between the two atoms moves one unit of negative charge from one atom to the other. As you can see on the right in Figure 2.7A, sodium, with 11 protons but now only 10 electrons, has a net electrical charge of 1. Chlorine, having gained an extra electron, now has 18 electrons but only 17 protons, giving it a net electrical charge of 1. In each case, an atom has become what is called an ion. An ion is an atom or molecule with an electrical charge resulting from a gain or loss of one or more electrons. (As shown in the figure, the ion formed from chlorine is called a chloride ion.) Two ions with opposite charges attract each other. When the attraction holds them together, it is called

?

Explain what holds together the atoms in a crystal of table salt (NaCl).

● Opposite charges attract. The positively charged sodium ions (Na) and the negatively charged chloride ions (Cl) are held together by ionic bonds, attractions between oppositely charged ions.

Transfer of electron

Cl– Na+



Na

Na Sodium atom

Cl

Na

Cl Chlorine atom

Na Sodium ion



Cl 

Cl Chloride ion

Sodium chloride (NaCl)

 Figure 2.7A Formation of an ionic bond, producing sodium chloride

 Figure 2.7B A crystal of sodium chloride

2.8 Hydrogen bonds are weak bonds important in the chemistry of life In living organisms, most of the strong chemical bonds are covalent, linking atoms to form a cell’s molecules. But crucial to the functioning of a cell are weaker bonds within and between molecules, such as the ionic bonds we just discussed. Most large molecules are held in their three-dimensional shape by weak bonds. In addition, molecules in a cell may be held together briefly by weak bonds, respond to one another in some way, and then separate. As you saw in Module 2.6, a hydrogen atom that has formed a polar covalent bond with an electronegative atom (such as oxygen or nitrogen) has a partial positive charge. 24

CHAPTER 2

The Chemical Basis of Life

This partial positive charge allows it to be attracted to a nearby partially negative atom (often an oxygen or nitrogen) of another molecule. These weak but important bonds are best illustrated with water molecules, as shown in Figure 2.8. The charged regions on each water molecule are electrically attracted to oppositely charged regions on neighboring molecules. Because the positively charged region in this special type of bond is always a hydrogen atom, the bond is called a hydrogen bond. As Figure 2.8 shows, the negative (oxygen) pole of a water molecule can form hydrogen bonds (dotted lines) to two hydrogen atoms. And each hydrogen atom of

(–) Hydrogen bond (+) H

(+)

O

(–)

H (–)

(+) (–)

a water molecule can form a hydrogen bond with a nearby partial negative oxygen atom of another water molecule. Thus, each H2O molecule can hydrogen-bond to as many as four partners. You will learn in Chapter 3 how hydrogen bonds help to create a protein’s shape (and thus its function) and hold the two strands of a DNA molecule together. Later in this chapter, we explore how water’s polarity and hydrogen bonds give it unique, life-supporting properties. But first we discuss how the making and breaking of bonds change the composition of matter.

(+)

?

 Figure 2.8 Hydrogen bonds between water molecules

What enables neighboring water molecules to hydrogen-bond to one another?

● The molecules are polar, with the negative end (oxygen end) of one molecule attracted to a positive end (hydrogen end) of its neighbor.

2.9 Chemical reactions make and break chemical bonds The basic chemistry of life has an overarching theme: The structure of atoms and molecules determines the way they behave. As we have seen, the chemical behavior of an atom is determined by the number and arrangement of its subatomic particles, particularly its electrons. Other properties emerge when atoms combine to form molecules and when molecules interact. Water is a good example, because its emergent properties sustain all life on Earth. Hydrogen and oxygen gases can react to form water: 2 H2 + O2

2 H2O

This is a chemical reaction, the breaking and making of chemical bonds, leading to changes in the composition of matter. In this case, two molecules of hydrogen (2 H2) react with one molecule of oxygen (O2) to produce two molecules of water (2 H2O). The arrow indicates the conversion of the starting materials, called the reactants, to the product, the material resulting from the chemical reaction. Notice that the same numbers of hydrogen and oxygen atoms appear on the left and right sides of the arrow, although they are grouped differently. Chemical reactions do not create or destroy matter; they only rearrange it in various ways. As 2 H2



O2

2 H2O

shown in Figure 2.9, the covalent bonds (represented here as white “sticks” between atoms) holding hydrogen atoms together in H2 and holding oxygen atoms together in O2 are broken, and new bonds are formed to yield the H2O product molecules. Organisms cannot make water from H2 and O2, but they do carry out a great number of chemical reactions that rearrange matter in significant ways. Let’s examine a chemical reaction that is essential to life on Earth: photosynthesis. The raw materials of photosynthesis are carbon dioxide (CO2), which is taken from the air, and water (H2O), which plants absorb from the soil. Within green plant cells, sunlight powers the conversion of these reactants to the sugar product glucose (C6H12O6) and oxygen (O2), a by-product that the plant releases into the air. The following chemical shorthand summarizes the process: 6 CO2 + 6 H2O

Although photosynthesis is actually a sequence of many chemical reactions, we see that we end up with the same number and kinds of atoms we started with. Matter has simply been rearranged, with an input of energy provided by sunlight. The chemistry of life is dynamic. Living cells routinely carry out thousands of chemical reactions. These reactions take place in the watery environment of a cell, and we look at the lifesupporting properties of water next.

?



Fill in the blanks with the correct numbers in the following chemical process: C6H12O6 + __O2

Products

 Figure 2.9 Breaking and making of bonds in a chemical reaction

__CO2 + __H2O

What process do you think this reaction represents? (Hint: Think about how your cells use these reactants to produce energy.) ● C6H12O6 + 6 O2 6 CO2 + 6 H2O; the breakdown of sugar in the presence of oxygen to carbon dioxide and water, with the release of energy that the cell can use

Reactants

C6H12O6 + 6 O2

Chemical Bonds

25

Water’s Life-Supporting Properties 2.10 Hydrogen bonds make liquid water cohesive  Figure 2.10 Surface tension allows a water strider to walk on water.

Hydrogen bonds give water unusually high surface tension, making it behave as though it were coated with an invisible film. You can observe the surface tension of water by slightly overfilling a glass; the water will stand above the rim. The water strider in Figure 2.10 takes advantage of the high surface tension of water to “stride” across ponds without breaking the surface.

?

After a hard workout, you may see “beads” of sweat on your face. Can you explain what holds the sweat in droplet form?

● The cohesion of water molecules and its high surface tension hold water in droplets. The adhesion of water to your skin helps hold the beads in place.

We can trace water’s life-supporting properties to the structure and interactions of its molecules—their polarity and resulting hydrogen bonding between molecules (review Figure 2.8). Hydrogen bonds between molecules of liquid water last for only a few trillionths of a second, yet at any instant, many molecules are hydrogen-bonded to others. This tendency of molecules of the same kind to stick together, called cohesion, is much stronger for water than for most other liquids. The cohesion of water is important in the living world. Trees, for example, depend on cohesion to help transport water and nutrients from their roots to their leaves. The evaporation of water from a leaf exerts a pulling force on water within the veins of the leaf. Because of cohesion, the force is relayed all the way down to the roots. Adhesion, the clinging of one substance to another, also plays a role. The adhesion of water to the cell walls of a plant’s thin veins helps counter the downward pull of gravity. Related to cohesion is surface tension, a measure of how difficult it is to stretch or break the surface of a liquid.

2.11 Water’s hydrogen bonds moderate temperature

26

CHAPTER 2

The Chemical Basis of Life

 Figure 2.11 Evaporative cooling occurs as sweat dries.

for approximately 66% of your body weight, it also helps moderate your temperature. When a substance evaporates (changes physical state from a liquid to a gas), the surface of the liquid that remains behind cools down. This evaporative cooling occurs because the molecules with the greatest energy (the “hottest” ones) leave. It’s as if the 10 fastest runners on the track team left school, lowering the average speed of the remaining team. Evaporative cooling helps prevent some land-dwelling organisms from overheating. Evaporation from a plant’s leaves keeps them from becoming too warm in the sun, just as sweating helps dissipate our excess body heat (Figure 2.11). On a much larger scale, the evaporation of surface waters cools tropical seas.

?

Explain the popular adage “It’s not the heat, it’s the humidity.” ● High humidity hampers cooling by slowing the evaporation of sweat.

If you have ever burned your finger on a metal pot while waiting for the water in it to boil, you know that water heats up much more slowly than metal. In fact, because of hydrogen bonding, water has a stronger resistance to temperature change than most other substances. Temperature and heat are related but different. A swimmer crossing San Francisco Bay has a higher temperature than the water, but the bay contains far more heat because of its immense volume. Heat is the amount of energy associated with the movement of atoms and molecules in a body of matter. Temperature measures the intensity of heat—that is, the average speed of molecules rather than the total amount of heat energy in a body of matter. Heat must be absorbed in order to break hydrogen bonds, and heat is released when hydrogen bonds form. To raise the temperature of water, heat energy must first disrupt hydrogen bonds before water molecules can move faster. Thus, water absorbs a large amount of heat while warming up only a few degrees. Conversely, when water cools, more hydrogen bonds form, and a considerable amount of heat is released. Earth’s giant water supply moderates temperatures, helping to keep them within limits that permit life. Oceans, lakes, and rivers store a huge amount of heat from the sun during warm periods. Heat given off from gradually cooling water warms the air. That’s why coastal areas generally have milder climates than inland regions. Water’s resistance to temperature change also stabilizes ocean temperatures, creating a favorable environment for marine life. Since water accounts

2.12 Ice is less dense than liquid water Water exists on Earth in the form of a gas (water vapor), liquid, and solid. Unlike most substances, water is less dense as a solid than as a liquid. And as you might guess, this unusual property is due to hydrogen bonds. As water freezes, each molecule forms stable hydrogen bonds with its neighbors, holding them at “arm’s length” and creating a three-dimensional crystal. In Figure 2.12, compare the spaciously arranged molecules in the ice crystal with the more tightly packed molecules in the liquid water. The ice crystal has fewer molecules than an equal volume of liquid water. Therefore, ice is less dense and floats on top of liquid water. If ice sank, then eventually ponds, lakes, and even oceans would freeze solid. Instead, when a deep body of water cools, the floating ice insulates the water below from colder air above. This “blanket” prevents the water below from freezing and allows fish and many other aquatic forms of life to survive under the frozen surface. In the Arctic, this frozen surface serves as the winter hunting ground for polar bears (Figure 2.12). The shrinking of this ice cover as a result of global warming may doom these bears.

?

Ice Hydrogen bonds are stable.

Hydrogen bond

Liquid water Hydrogen bonds constantly break and re-form.

Explain how the freezing of water can crack boulders.  Figure 2.12 Hydrogen bonds between water molecules in

● Water in the crevices of a boulder expands as it freezes because the water molecules become spaced farther apart in forming ice crystals, cracking the rock.

ice and water

2.13 Water is the solvent of life If you add a teaspoon of table salt to a glass of water, the salt will dissolve and eventually become evenly mixed with the water, forming a solution. A solution is a liquid consisting of a uniform mixture of two or more substances. The dissolving agent (in this case, water) is the solvent, and a substance that is dissolved (salt) is a solute. An aqueous solution (from the Latin aqua, water) is one in which water is the solvent. Water’s versatility as a solvent results from the polarity of its molecules. Figure 2.13 shows how a teaspoon of salt

Na

Cl



 

  

   

  Na  

Cl 





Salt crystal  Figure 2.13 A crystal of salt (NaCl) dissolving in water

?

Why are blood and most other biological fluids classified as aqueous solutions? ● The solvent is water.

Ion in solution

dissolves in water. At the surface of each grain, or crystal, the sodium and chloride ions are exposed to water. These ions and the water molecules are attracted to each other due to their opposite charges. The oxygen ends (red) of the water molecules have a partial negative charge and cling to the positive sodium ions ( Na+). The hydrogens of the water molecules, with their partial positive charge, are attracted to the negative chloride ions ( Cl– ). Working inward from the surface of each salt crystal, water molecules eventually surround and separate all the ions. Water dissolves other ionic compounds as well. Seawater, for instance, contains a great variety of dissolved ions, as do your cells. A compound doesn’t need to be ionic to dissolve in water. A spoonful of sugar will also dissolve in a glass of water. Polar molecules such as sugar dissolve as water molecules surround them and form hydrogen bonds with their polar regions. Even large molecules, such as proteins, can dissolve if they have ionic or polar regions on their surface. As the solvent inside all cells, in blood, and in plant sap, water dissolves an enormous variety of solutes necessary for life.

Water’s Life-Supporting Properties

27

2.14 The chemistry of life is sensitive to acidic and basic conditions

Increasingly BASIC (Higher OH concentration )

Increasingly ACIDIC (Higher H concentration)

In aqueous solutions, a very small percentage of the pH scale water molecules actually break apart (dissociate) into  0 ions. The ions formed are called hydrogen ions (H )  H H and hydroxide ions (OH ). Hydrogen and hydroxide Battery acid ions are very reactive. The proper balance of these ions H OH H 1 is critical for the chemical processes that occur within OH H an organism. H H  H Some chemical compounds contribute additional Lemon juice, 2 H to an aqueous solution, whereas others remove H Acidic solution gastric juice from it. A compound that donates hydrogen ions to solutions is called an acid. One example of a strong acid is Vinegar, cola 3 hydrochloric acid (HCl), the acid in the gastric juice in your stomach. In solution, HCl dissociates completely into H and Cl. An acidic solution has a higher conTomato juice 4 centration of H than OH. A base is a compound that accepts hydrogen ions and removes them from solution. Some bases, such as 5 sodium hydroxide (NaOH), do this by donating OH;    the OH combines with H to form H2O, thus reducOH H OH Rainwater  ing the H concentration. Sodium hydroxide, also  H OH Human urine 6 called lye, is a common ingredient in oven cleaners. The OH   OH more basic a solution, the higher its OH concentraH H Saliva H tion and the lower its H concentration. Basic solutions NEUTRAL Pure water 7 are also called alkaline solutions. [H][OH] Neutral solution We use the pH scale to describe how acidic or basic Human blood, tears a solution is (pH stands for potential of hydrogen). As 8 shown in Figure 2.14, the scale ranges from 0 (most Seawater acidic) to 14 (most basic). Each pH unit represents a 10-fold change in the concentration of H in a solu9 tion. For example, lemon juice at pH 2 has 10 times more H than an equal amount of a cola at pH 3 and 100 times more H than tomato juice at pH 4. Pure water and aqueous solutions that are neither 10 acidic nor basic are said to be neutral; they have a pH of OH OH Milk of magnesia 7. They do contain some hydrogen and hydroxide ions, OH H OH but the concentrations of the two kinds of ions are equal. 11 OH The pH of the solution inside most living cells is close to  OH OH Household ammonia H 7. Even a slight change in pH can be harmful because the proteins and other complex molecules in cells are ex12 Basic solution tremely sensitive to the concentrations of H and OH. Household bleach The pH of human blood plasma (the fluid portion of the blood) is very close to 7.4. A person cannot survive 13 for more than a few minutes if the blood pH drops to Oven cleaner 7.0 or rises to 7.8. If you add a small amount of a strong acid to a liter of pure water, the pH drops from 7.0 to 2.0. 14 If the same amount of acid is added to a liter of blood,  Figure 2.14 The pH scale reflects the relative concentrations of H and OH. however, the pH decrease is only from 7.4 to 7.3. How can the acid have so much less effect on the pH of blood? Biological fluids contain buffers, substances that minimize changes in pH. They do so by accepting H when it is in excess and donating H when it is depleted. There are several types of buffers that contribute to the pH stability in ? Compared to a basic solution at pH 9, the same volume of an acidic solution at pH 4 has ______ times more hydrogen blood and many other internal solutions. ions (H+). In the next module, we explore how changes in acidity can have environmental consequences. ● 100,000

28

CHAPTER 2

The Chemical Basis of Life

CONNECTION

2.15 Acid precipitation and ocean acidification threaten

the environment

process called calcification. Coral reef ecosystems act as havens for a great diversity of organisms (Figure 2.15). Other calcifying organisms are important food sources for salmon, herring, and other ocean fishes. Decreased calcification is likely to affect marine food webs and may substantially alter the productivity and biodiversity of Earth’s oceans.

?

What is the relationship between fossil fuel consumption and coral reefs?

2.16 The search for extraterrestrial life centers on the search for water

When astrobiologists search for signs of extraterrestrial life on distant planets, they look for evidence of water. Why? As we’ve seen in this chapter, the emergent properties of water (its cohesion, ability to moderate temperature and insulate, and versatility as a solvent) support life on Earth in many ways. Is it possible that some form of life has evolved on other planets that have water in their environment? Researchers with the National Aeronautics and Space Administration (NASA) have found evidence that water was once abundant on Mars. In January 2004, NASA succeeded in landing two golf-cart-sized rovers, named Spirit and Opportunity, on Mars. These robotic geologists, using sophisticated instruments to determine the composition of rocks, detected a mineral that is formed only in the presence of water. And pictures sent back from the rovers and various orbiting Mars spacecraft have revealed physical evidence of past water. In 2008, an analysis of Martian soil by the Phoenix Mars Lander provided evidence that components of the soil had at one time been dissolved in water. Figure 2.16 shows a robotic arm of Phoenix that has gathered samples and scraped trenches that exposed ice just below the surface on Mars.

 Figure 2.16 Robotic arm of the Phoenix Mars Lander probing for evidence of water

No evidence for life on Mars has yet been found. But is it possible that life is not unique to planet Earth? Chapter 15 presents evidence that life could originate in the environment of early Earth. Finding evidence of life elsewhere would support the hypothesis that the chemical evolution of life is possible.

?

Why is the presence of water important in the search for extraterrestrial life?

● Water plays important roles in life as we know it, from moderating temperatures on the planet to functioning as the solvent of life.

EVOLUTION CONNECTION

 Figure 2.15 Coral reefs are threatened by ocean acidification.

● Some of the increased CO2 released by burning fossil fuels dissolves in and lowers the pH of the oceans. A lower pH reduces levels of carbonate ions, which then lowers the rate of calcification by coral animals.

Considering the dependence of all life on water, contamination of rivers, lakes, seas, and precipitation poses serious environmental problems. The burning of fossil fuels (coal, oil, and gas), which releases air-polluting compounds and large amounts of CO2 into the atmosphere, is among the many threats to water quality posed by human activities. Chemical reactions of these compounds with water increase acidity and alter the delicate balance of conditions for life on Earth. Sulfur oxides and nitrogen oxides released by burning fossil fuels react with water in the air to form strong acids, which fall to Earth with rain or snow. Acid precipitation refers to rain, snow, or fog with a pH lower than 5.2 (the pH of uncontaminated rain is 5.6). Acid precipitation has damaged life in lakes and streams and adversely affected plants through changes in soil chemistry. In the United States, amendments made in 1990 to the Clean Air Act have reduced acid precipitation and improved the health of most North American lakes and forests. Carbon dioxide is the main product of fossil fuel combustion, and its steadily increasing release into the atmosphere is linked to global climate change (see Module 38.6). About 25% of human-generated CO2 is absorbed by the oceans. An increase in CO2 absorption is expected to change ocean chemistry and harm marine life and ecosystems. In ocean acidification, CO2 dissolving in seawater lowers ocean pH. That’s because CO2 reacts with water to produce carbonic acid (H2CO3). The change in acidity decreases the concentration of carbonate ions, which are required by corals and other organisms to produce their skeletons or shells, a

Water’s Life-Supporting Properties

29

C H A P T E R

2

R E V I E W

For Practice Quizzes, BioFlix, MP3 Tutors, and Activities, go to www.masteringbiology.com.

The chemistry of life is sensitive to acidic and basic conditions. A compound that releases H in solution is an acid, 2.14

Reviewing the Concepts Elements, Atoms, and Compounds (2.1–2.4) Organisms are composed of elements, in combinations called compounds. Oxygen, carbon, hydrogen, and nitrogen

2.1

make up about 96% of living matter. 2.2 2.3

Trace elements are common additives to food and water. Atoms consist of protons, neutrons, and electrons.

Protons (+ charge) determine element Neutrons (no charge) determine isotope 2.4

 

Water is the solvent of life. Polar or charged solutes dissolve when water molecules surround them, forming aqueous solutions.

2.13

 

Atom

and one that accepts H is a base. The pH scale ranges from 0 (most acidic) to 14 (most basic). The pH of most cells is close to 7 (neutral) and kept that way by buffers. Acid precipitation and ocean acidification threaten the environment. The burning of fossil fuels increases the amount of CO2

2.15

in the atmosphere and dissolved in the oceans. The acidification of the ocean threatens coral reefs and other marine organisms. The search for extraterrestrial life centers on the search for water. The emergent properties of water support life on Earth and may contribute to the potential for life to have evolved on other planets.

Nucleus

2.16

Electrons (– charge) form negative cloud and determine chemical behavior

Connecting the Concepts

Radioactive isotopes can help or harm us. Radioactive

1. Fill in the blanks in this concept map to help you tie together the key concepts concerning elements, atoms, and molecules.

isotopes are valuable in basic research and medicine. Atoms

Chemical Bonds (2.5–2.9) have positively charged

The distribution of electrons determines an atom’s chemical properties. An atom whose outer electron shell is not full tends to

2.5

interact with other atoms and share, gain, or lose electrons, resulting in attractions called chemical bonds.

(a) number present equals

In polar covalent bonds, such as those found in water, electrons are pulled closer to the more electronegative atom.

atomic number of each element

2.7

have negatively charged

(b)

Covalent bonds join atoms into molecules through electron sharing. In a nonpolar covalent bond, electrons are shared equally.

2.6

have neutral

(c) number may differ in

number in outer shell determines formation of 

(d)

H

Ionic bonds are attractions between ions of opposite charge.

Electron gain and loss create charged atoms, called ions. Hydrogen bonds are weak bonds important in the chemistry of life. The slightly positively charged H atoms in one polar

2.8

Chemical Bonds

molecule may be attracted to the partial negative charge of an O or N atom in a neighboring molecule. 2.9 Chemical reactions make and break chemical bonds. The composition of matter is changed as bonds are broken and formed to convert reactants to products.

electron transfer between atoms creates



ions

Hydrogen bonds make water molecules cohesive. Cohesion

creates surface tension and allows water to move from plant roots to leaves. 2.11 Water’s hydrogen bonds moderate temperature. Heat is absorbed when hydrogen bonds break and released when hydrogen bonds form. This helps keep temperatures relatively steady. As the most energetic water molecules evaporate, the surface of a substance cools. 2.12 Ice is less dense than liquid water. Floating ice protects lakes and oceans from freezing solid.

attraction between ions creates (f)

30

CHAPTER 2

The Chemical Basis of Life

equal sharing creates

nonpolar covalent bonds

H

O

can lead to

example is

() ()

H

O

()

water

Ice: Stable hydrogen bonds

unequal sharing creates

()

H

H

(e)

(g)

()

Liquid water: Hydrogen bonds form and break

H

Cl

Na

Water’s Life-Supporting Properties (2.10–2.16) 2.10

electron sharing between atoms creates

has important qualities due to polarity and

(h)

2. Create a concept map to organize your understanding of the life-supporting properties of water. A sample map is in the answer section, but the value of this exercise is in the thinking and integrating you must do to create your own map.

Testing Your Knowledge Multiple Choice 3. Changing the ______ would change it into an atom of a different element. a. number of electrons surrounding the nucleus of an atom b. number of bonds formed by an atom c. number of protons in the nucleus of an atom d. electrical charge of an atom e. number of neutrons in the nucleus of an atom 4. Your body contains the smallest amount of which of the following elements? a. nitrogen c. carbon e. hydrogen b. phosphorus d. oxygen 5. A solution at pH 6 contains ______ than the same amount of a solution at pH 8. a. 2 times more H b. 4 times more H c. 100 times more H d. 4 times less H e. 100 times less H

True/False (Change false statements to make them true.) 11. Table salt, water, and carbon are compounds. 12. The smallest unit of an element is a molecule. 13. A bathtub full of lukewarm water may hold more heat than a teakettle full of boiling water. 14. If the atoms in a molecule share electrons equally, the molecule is said to be nonpolar. 15. Ice floats because water molecules in ice are more tightly packed than in liquid water. 16. Atoms in a water molecule are held together by the sharing of electrons. 17. Most acid precipitation results from the presence of pollutants from aerosol cans and air conditioners. 18. An atom that has gained or lost electrons is called an ion.

Describing, Comparing, and Explaining 19. Make a sketch that shows how water molecules hydrogen-bond with one another. Why do water molecules form hydrogen bonds? What unique properties of water result from water’s tendency to form hydrogen bonds?

6. Most of the unique properties of water result from the fact that water molecules a. are very small. b. are held together by covalent bonds. c. easily separate from one another. d. are constantly in motion. e. are polar and form hydrogen bonds.

Applying the Concepts

7. A sulfur atom has 6 electrons in its outer shell. As a result, it forms ______ covalent bonds with other atoms. (Explain your answer.) a. two c. four e. eight b. three d. six

23. The diagram below shows the arrangement of electrons around the nucleus of a fluorine atom (left) and a potassium atom (right). What kind of bond do you think would form between these two atoms?

8. What does the word trace mean when you’re talking about a trace element? a. The element is required in very small amounts. b. The element can be used as a label to trace atoms through an organism’s body. c. The element is very rare on Earth. d. The element enhances health but is not essential for the organism’s long-term survival. e. The element passes rapidly through the organism. 9. A can of cola consists mostly of sugar dissolved in water, with some carbon dioxide gas that makes it fizzy and makes the pH less than 7. In chemical terms, you could say that cola is an aqueous solution where water is the ______, sugar is a ______, and carbon dioxide makes the solution ______. a. solvent ... solute ... basic b. solute ... solvent ... basic c. solvent ... solute ... acidic d. solute ... solvent ... acidic e. not enough information to say 10. Radioactive isotopes can be used in medical studies because a. they allow researchers to time how long processes take. b. they are more reactive than nonradioactive isotopes. c. the cell does not recognize the extra protons in the nucleus, so isotopes are readily used in cellular processes. d. their location or quantity can be determined because of their radioactivity. e. their extra neutrons produce different colors that can be traced through the body.

20. Describe two ways in which the water in your body helps stabilize your body temperature. 21. Compare covalent and ionic bonds. 22. What is an acid? A base? How is the acidity of a solution described?

F

K

Fluorine atom

Potassium atom

24. Look back at the abbreviated periodic table of the elements in Figure 2.5. If two or more elements are in the same row, what do they have in common? If two elements are in the same column, what do they have in common? 25