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Today & Tomorrow

5e

Cecie Starr | Christine A. Evers | Lisa Starr

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1 Invitation to Biology

Unit 1 How Cells work

2 Molecules of Life

3 Cell Structure

4 Energy and Metabolism

5 Capturing and Releasing Energy

Unit 2 GenetiCs

6 DNA Structure and Function

7 Gene Expression and Control

8 How Cells Reproduce

9 Patterns of Inheritance

10 Biotechnology

Unit 3 evolUtion and diversity

11 Evidence of Evolution

12 Processes of Evolution

13 Early Life Forms and the Viruses

14 Plants and Fungi

15 Animal Evolution

Unit 4 eColoGy

16 Population Ecology

17 Communities and Ecosystems

18 The Biosphere and Human Effects

Unit 5 How animals work

19 Animal Tissues and Organs

20 How Animals Move

21 Circulation and Respiration

22 Immunity

23 Digestion and Excretion

24 Neural Control and the Senses

25 Endocrine Control

26 Reproduction and Development

Unit 6 How Plants work

27 Plant Form and Function

28 Plant Reproduction and Development

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1 Invitation to Biology 1.1 the secret life of earth 4

1.2 life is more than the sum of its Parts 4

1.3 How living things are alike 6

Organisms Require Energy and Nutrients 6

Organisms Sense and Respond to Change 6

Organisms Grow and Reproduce 6

1.4 How living things differ 8

What Is a Species? 8

A Rose by Any Other Name 10

1.5 the science of nature 11

Thinking About Thinking 12

How Science Works 12

Examples of Experiments in Biology 13

1.6 the nature of science 16

Bias in Interpreting Experimental Results 16

Sampling Error 17

Scientific Theories 18

The Scope of Science 19

UNIT 1 HOw CELLS wORk

2 Molecules of Life 2.1 Fear of Frying 24

2.2 start with atoms 25

Why Electrons Matter 26

2.3 From atoms to molecules 28

Ionic Bonds 28

Covalent Bonds 28

2.4 Hydrogen Bonds and water 29

Water Is an Excellent Solvent 30

Water Has Cohesion 31

Water Stabilizes Temperature 31

2.5 acids and Bases 32

2.6 organic molecules 33

What Cells Do to Organic Compounds 33

2.7 Carbohydrates 34

2.8 lipids 36

Fats 36

Phospholipids 36

Waxes 37

Steroids 37

2.9 Proteins 38

The Importance of Protein Structure 39

2.10 nucleic acids 41

3 Cell Structure 3.1 Food for thought 46

3.2 what, exactly, is a Cell? 46

The Cell Theory 46

Components of All Cells 47

Constraints on Cell Size 47

How Do We See Cells? 48

3.3 Cell membrane structure 50

Membrane Proteins 51

3.4 introducing Prokaryotic Cells 52

Biofilms 53

3.5 introducing eukaryotic Cells 54

The Nucleus 54

The Endomembrane System 54

Mitochondria 55

Chloroplasts 56

The Cytoskeleton 56

Extracellular Matrix 58

Cell Junctions 58

3.6 the nature of life 59

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4 Energy and Metabolism 4.1 a toast to alcohol dehydrogenase 64

4.2 life runs on energy 65

4.3 energy in the molecules of life 66

Why Earth Does Not Go Up in Flames 67

Energy In, Energy Out 68

4.4 How enzymes work 68

The Need for Speed 68

Factors That Influence Enzyme Activity 69

Cofactors 70

Metabolic Pathways 71

Controlling Metabolism 71

Electron Transfers 72

4.5 diffusion and membranes 73

Semipermeable Membranes 73

4.6 membrane transport mechanisms 75

Passive Transport 75

Active Transport 76

Membrane Trafficking 76

5 Capturing and Releasing Energy

5.1 a Burning Concern 82

5.2 to Catch a rainbow 83

Storing Energy in Sugars 84

5.3 light-dependent reactions 85

5.4 light-independent reactions 87

Alternative Carbon-Fixing Pathways 87

5.5 a Global Connection 89

Aerobic Respiration in Mitochondria 89

5.6 Fermentation 92

5.7 Food as a source of energy 94

Complex Carbohydrates 94

Fats 94

Proteins 95

UNIT 2 GENETICS

6 DNA Structure and Function 6.1 Cloning 100

6.2 Fame, Glory, and dna structure 102

Discovery of DNA’s Function 102

Discovery of DNA’s Structure 104

DNA Sequence 105

6.3 dna in Chromosomes 106

6.4 dna replication and repair 108

How Mutations Arise 108

7 Gene Expression and Control 7.1 ricin, riP 114

7.2 Gene expression 115

7.3 transcription: dna to rna 116

RNA Modifications 117

7.4 the Genetic Code 118

7.5 translation: rna to Protein 119

7.6 Products of mutated Genes 122

7.7 Control of Gene expression 124

Master Genes 124

Sex Chromosome Genes 125

Lactose Tolerance 125

DNA Methylation 126

CONTENTS v

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8 How Cells Reproduce 8.1 Henrietta’s immortal Cells 132

8.2 multiplication by division 133

Cytoplasmic Division 136

8.3 mitosis and Cancer 137

Cell Division Gone Wrong 137

Cancer 138

Telomeres 139

8.4 sex and alleles 140

On the Advantages of Sex 140

8.5 meiosis in sexual reproduction 142

How Meiosis Mixes Alleles 144

From Gametes to Offspring 144

9 Patterns of Inheritance 9.1 menacing mucus 150

9.2 tracking traits 151

Mendel’s Experiments 151

Inheritance in Modern Terms 151

9.3 mendelian inheritance Patterns 152

Monohybrid Crosses 153

Dihybrid Crosses 154

9.4 Beyond simple dominance 155

Incomplete Dominance 155

Codominance 155

Pleiotropy and Epistasis 156

9.5 Complex variation in traits 158

Continuous Variation 159

9.6 Human Genetic analysis 160

Types of Genetic Variation 160

9.7 Human Genetic disorders 161

The Autosomal Dominant Pattern 162

The Autosomal Recessive Pattern 163

The X-Linked Recessive Pattern 164

9.8 Chromosome number Changes 165

Autosomal Change and Down Syndrome 166

Change in the Sex Chromosome Number 166

9.9 Genetic screening 168

10 Biotechnology 10.1 Personal Genetic testing 174

10.2 Finding needles in Haystacks 175

Cutting and Pasting DNA 175

DNA Libraries 176

PCR 177

10.3 studying dna 178

Sequencing the Human Genome 178

Genomics 179

DNA Profiling 179

10.4 Genetic engineering 181

Genetically Modified Microorganisms 181

Designer Plants 181

Biotech Barnyards 182

10.5 modifying Humans 184

Gene Therapy 184

Eugenics 185

UNIT 3 EVOLUTION AND DIVERSITy

11 Evidence of Evolution 11.1 reflections of a distant Past 190

11.2 Confusing discoveries 191

11.3 a Flurry of new ideas 192

Squeezing New Evidence Into Old Beliefs 192

Darwin and the HMS Beagle 193

A Key Insight—Variation in Traits 194

Great Minds Think Alike 195

11.4 Fossil evidence 196

The Fossil Record 196

vi CONTENTS

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CONTENTS vii

Radiometric Dating 197

Missing Links 199

11.5 drifting Continents 200

Putting Time Into Perspective 201

11.6 evidence in Form 204

Morphological Divergence 204

Morphological Convergence 205

11.7 evidence in Function 206

Patterns in Animal Development 207

12 Processes of Evolution 12.1 superbug Farms 212

12.2 alleles in Populations 213

An Evolutionary View of Mutations 213

Allele Frequency 214

12.3 modes of natural selection 215

Directional Selection 215

Stabilizing Selection 217

Disruptive Selection 217

12.4 natural selection and diversity 218

Survival of the Sexiest 218

Maintaining Multiple Alleles 219

12.5 Genetic drift and Gene Flow 220

Bottlenecks and the Founder Effect 220

Gene Flow 221

12.6 speciation 222

Reproductive Isolation 222

Allopatric Speciation 224

Sympatric Speciation 224

12.7 macroevolution 226

Evolutionary Theory 228

12.8 Phylogeny 229

Applications of Phylogeny 230

13 Early Life Forms and the Viruses 13.1 the Human micobiome 236

13.2 on the road to life 237

Conditions on the Early Earth 237

Origin of the Building Blocks of Life 237

Origin of Metabolism 238

Origin of Genetic Material 238

Origin of Cell Membranes 239

13.3 origin of the three domains 240

Reign of the Prokaryotes 240

Origin of Eukaryotes 241

13.4 viruses 242

Viral Structure and Replication 242

Bacteriophages 242

Plant Viruses 243

Viruses and Human Health 243

HIV—The AIDS Virus 244

Ebola 245

New Flus 245

13.5 Bacteria and archaea 246

Structure and Function 246

Reproduction and Gene Transfers 246

Metabolic Diversity 247

Domain Archaea 248

Domain Bacteria 248

13.6 Protists 250

Flagellated Protozoans 250

Foraminifera 251

Ciliates 251

Dinoflagellates 252

Apicomplexans 252

Water Molds, Diatoms, and Brown Algae 254

Red Algae 255

Green Algae 255

Amoebas and Slime Molds 256

Choanoflagellates 257

14 Plants and Fungi 14.1 Fungal threats to Crops 262

14.2 Plant traits and evolution 263

Life Cycle 263

Structural Adaptations to Life on Land 264

Reproduction and Dispersal 264

14.3 nonvascular Plants 265

Mosses 265

Liverworts and Hornworts 266

14.4 seedless vascular Plants 266

Ferns 266

Horsetails and Club Mosses 267

14.5 rise of the seed Plants 269

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14.6 Gymnosperms 270

Conifers 270

Cycads and Ginkgos 271

Gnetophytes 271

14.7 angiosperms—Flowering Plants 272

Floral Structure and Function 272

A Flowering Plant Life Cycle 273

Keys to Angiosperm Diversity 273

Major Groups 273

Ecology and Human Uses of Angiosperms 274

14.8 Fungal traits and diversity 274

Yeasts, Molds, Mildews, and Mushrooms 274

Lineages and Life Cycles 275

14.9 ecological roles of Fungi 277

Decomposers 277

Parasites 277

Fungal Partnerships 278

Human Uses of Fungi 279

15 Animal Evolution 15.1 medicines From the sea 284

15.2 origins and diversification 285

Animal Origins 285

Evidence of Early Animals 285

Major Groups and Evolutionary Trends 286

15.3 invertebrate diversity 288

Sponges 288

Cnidarians 288

Flatworms 289

Annelids 290

Mollusks 290

Roundworms 291

Arthropods 292

Echinoderms 296

15.4 introducing the Chordates 297

Chordate Traits 297

Invertebrate Chordates 297

Vertebrate Traits and Trends 298

15.5 Fishes and amphibians 299

Jawless Fishes 299

Jawed Fishes 299

Early Tetrapods 300

Modern Amphibians 301

15.6 escape From water—amniotes 302

Amniote Innovations 302

Nonbird Reptiles 302

Birds 303

Mammals 303

15.7 Human evolution 305

Primate Traits 305

Primate Origins and Diversification 305

Australopiths 306

Early Humans 307

Homo Sapiens 308

Neanderthals and Denisovans 308

UNIT 4 ECOLOGy

16 Population Ecology 16.1 a Honkin’ mess 314

16.2 Characteristics of Populations 315

Demographic Traits 315

Collecting Demographic Data 316

16.3 Population Growth 317

Exponential Growth 317

Carrying Capacity and Logistic Growth 318

Density-Independent Factors 319

16.4 life History Patterns 320

Biotic Potential 320

Describing Life Histories 320

Evolution of Life Histories 321

Predation and Life History Evolution 322

viii CONTENTS

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CONTENTS ix

16.5 Human Populations 323

Population Size and Growth Rate 323

Fertility Rates and Future Growth 324

Effects of Industrial Development 325

17 Communities and Ecosystems 17.1 Fighting Foreign Fire ants 330

17.2 Community structure 331

Nonbiological Factors 331

Biological Factors 331

17.3 direct species interactions 332

Commensalism and Mutualism 332

Interspecific Competition 333

Predator–Prey Interactions 334

Plants and Herbivores 335

Parasites and Parasitoids 335

17.4 How Communities Change 337

Ecological Succession 337

Adapted to Disturbance 338

Species Losses or Additions 338

17.5 the nature of ecosystems 339

Overview of the Participants 339

Food Chains and Webs 339

Primary Production and Inefficient Energy Transfers 341

17.6 Biogeochemical Cycles 342

The Water Cycle 342

The Phosphorus Cycle 342

The Nitrogen Cycle 344

The Carbon Cycle 345

The Greenhouse Effect and Global Climate Change 346

18 The Biosphere and Human Effects 18.1 Going with the Flow 352

18.2 Factors that affect Climate 353

Air Circulation Patterns 353

Ocean Circulation 354

18.3 the major Biomes 355

Forest Biomes 355

Grasslands and Chaparral 356

Deserts 356

Tundra 356

18.4 aquatic ecosystems 358

Freshwater Ecosystems 358

Marine Ecosystems 358

18.5 Human impact on the Biosphere 360

Increased Species Extinctions 360

Deforestation and Desertification 362

Acid Rain 362

Biological Accumulation and Magnification 363

The Trouble With Trash 363

Destruction of the Ozone Layer 364

Global Climate Change 364

18.6 maintaining Biodiversity 366

The Value of Biodiversity 366

Conservation Biology 366

Ecological Restoration 367

Reducing Human Impacts 368

UNIT 5 HOw ANIMALS wORk

19 Animal Tissues and Organs 19.1 Growing replacement Parts 374

19.2 animal structure and Function 375

Organization and Integration 375

Evolution of Structure and Function 376

19.3 types of animal tissues 376

Epithelial Tissues 376

Connective Tissues 378

Muscle Tissues 379

Nervous Tissue 380

19.4 organs and organ systems 380

Organ Systems 382

19.5 regulating Body temperature 384

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20 How Animals Move 20.1 Bulking Up muscles 390

20.2 skeletal systems 391

Types of Skeletons 391

The Human Skeleton 392

Bone Structure and Function 392

Where Bones Meet—Skeletal Joints 393

20.3 Functions of skeletal muscles 395

20.4 How muscle Contracts 396

Muscle Components 396

Sliding Filaments 397

20.5 Fueling muscle Contraction 398

20.6 exercise and inactivity 398

21 Circulation and Respiration 21.1 a shocking save 404

21.2 How substances are moved through a Body 405

Open and Closed Circulatory Systems 405

Evolution of Vertebrate Cardiovascular Systems 406

21.3 Human Cardiovascular system 407

21.4 the Human Heart 408

The Cardiac Cycle 409

Setting the Pace of Contractions 409

21.5 Blood and Blood vessels 410

Components and Functions of Blood 410

High-Pressure Flow in Arteries 410

Adjusting Resistance at Arterioles 411

Capillary Exchange and Function of the Lymph Vessels 411

Back to the Heart 412

21.6 Blood and Cardiovascular disorders 412

Blood Disorders 412

Cardiovascular Disorders 413

21.7 animal respiration 414

Two Sites of Gas Exchange 414

Respiratory Systems 414

21.8 Human respiratory Function 416

From Airways to Alveoli 416

How You Breathe 417

Exchanges at Alveoli 418

Transport of Gases 418

Respiratory Disorders 418

22 Immunity 22.1 Frankie’s last wish 424

22.2 responding to threats 425

The Defenders 426

22.3 innate immunity mechanisms 427

Normal Flora 427

Surface Barriers 427

Complement 428

Phagocytosis 428

Inflammation and Fever 429

Examples of Innate Responses 430

22.4 antigen receptors 431

Antigen Processing 432

22.5 adaptive immune responses 434

Example of an Antibody-Mediated Response 434

Example of a Cell-Mediated Response 436

22.6 immunity Gone wrong 438

Overly Vigorous Responses 438

Immune Deficiency and AIDS 439

22.7 vaccines 441

23 Digestion and Excretion 23.1 Causes and effects of obesity 446

23.2 two types of digestive systems 446

23.3 digestive structure and Function 448

In the Mouth 448

Swallowing 448

The Stomach 449

Digestion in the Small Intestine 450

Absorption in the Small Intestine 451

Concentrating and Eliminating Wastes 452

23.4 Human nutrition 453

Carbohydrates 453

Fats 454

Proteins 454

Vitamins and Minerals 454

USDA Dietary Recommendations 455

23.5 Fluid regulation 456

Fluid Homeostasis 456

Fluid Regulation in Invertebrates 456

Vertebrate Urinary System 457

x CONTENTS

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CONTENTS xi

23.6 kidney Function 458

How Urine Forms 458

Feedback Control of Urine Formation 459

Impaired Kidney Function 460

24 Neural Control and the Senses 24.1 impacts of Concussions 466

24.2 animal nervous systems 467

Invertebrate Nervous Systems 467

Vertebrate Nervous Systems 467

24.3 neuron Function 468

Three Types of Neurons 468

Neuroglia—Neuron Helpers 469

Resting Potential 469

The Action Potential 470

The Chemical Synapse 471

Disrupted Synaptic Function 472

Psychoactive Drugs 472

24.4 the Central nervous system 474

Regions of the Human Brain 474

A Closer Look at the Cerebral Cortex 476

The Limbic System—Emotion and Memory 476

The Spinal Cord 477

24.5 the Peripheral nervous system 478

24.6 the senses 480

Sensory Reception and Diversity 480

Sensation to Perception 480

The Chemical Senses—Smell and Taste 481

Detecting Light 482

The Human Eye 482

At the Retina 484

Hearing 484

Sense of Balance 486

The Somatosensory Cortex 487

25 Endocrine Control 25.1 endocrine disrupters 492

25.2 Hormone Function 493

Types of Hormones 494

Hormone Receptors 494

25.3 the Hypothalamus and Pituitary 496

Posterior Pituitary Function 496

Anterior Pituitary Function 496

Growth Disorders 496

25.4 thyroid and Parathyroid Glands 498

Thyroid Hormone 498

Regulation of Calcium 499

25.5 the Pancreas 500

Controlling Blood Glucose 500

Diabetes Mellitus 501

25.6 the adrenal Glands 502

25.7 Hormones and reproductive Function 504

Gonads 504

The Pineal Gland 504

26 Reproduction and Development 26.1 assisted reproduction 510

26.2 modes of reproduction 511

Asexual Reproduction 511

Sexual Reproduction 511

Variations on Sexual Reproduction 511

26.3 stages of animal development 512

26.4 Human reproductive Function 514

Female Reproductive Anatomy 514

Egg Production and Release 515

The Menstrual Cycle 516

Male Reproductive Anatomy 517

How Sperm Form 518

Sexual Intercourse 518

A Sperm’s Journey 519

26.5 reproductive Health 520

Contraception 520

Infertility 521

Sexually Transmitted Diseases 522

26.6 Human development 523

Fertilization 523

From Cleavage to Implantation 524

Embryonic and Fetal Development 525

Functions of the Placenta 528

Maternal Effects on Prenatal Development 528

26.7 Birth and milk Production 529

Childbirth 529

Nourishing the Newborn 529

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UNIT 6 HOw PLANTS wORk

27 Plant Form and Function 27.1 leafy Cleanup Crews 534

27.2 tissues in a Plant Body 535

Eudicots and Monocots 537

27.3 stems, leaves, and roots 538

Stems 538

Leaves 540

Roots 542

27.4 Fluid movement in Plants 544

Water Moves Through Xylem 544

Sugars Flow Through Phloem 545

27.5 Plant Growth 546

28 Plant Reproduction and Development

28.1 Plight of the Honeybee 554

28.2 sexual reproduction 555

A New Generation Begins 558

28.3 seeds and Fruits 560

28.4 early development 562

28.5 asexual reproduction 564

Agricultural Applications 564

28.6 Plant Hormones 565

Auxin 566

Cytokinin 567

Gibberellin 568

Abscisic Acid 568

Ethylene 568

28.7 Growth responses 570

Tropisms 570

Photoperiodic Responses 572

appendix i answers to self-Quizzes

appendix ii Periodic table of the elements

appendix iii a Plain english map of the Human Chromosomes

appendix iv Units of measure

xii CONTENTS

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P

P r

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Biology is a huge field, with a wealth of new discover- ies being made every day, and biology-related issues such as climate change, stem cell research, and per- sonal genetics often making headlines. This avalanche of information can be intimidating to non-scientists. This book was designed and written specifically for students who most likely will not become biologists and may never again take another science course. It is an accessible and engaging introduction to biology that provides future decision-makers with an under- standing of basic biology and the process of science.

a wealth of applications This book is packed with everyday applications of biological processes. At every opportunity, we enliven discussions of biologi- cal processes with references to their effects on human health and the environment. This edition also con- tinues to focus on real world applications pertaining to the field of biology, including social issues arising from new research and developments. Descriptions of current research, along with photos of scientists who carry it out, underscore the concept that biology is an ongoing endeavor carried out by a diverse commu- nity of people. Discussions include not only what was discovered, but also how the discoveries were made, how our understanding has changed over time, and what remains to be discovered. These discussions are provided in the context of an accessible introduction to well-established concepts that underpin modern biology. Every topic is examined from an evolutionary perspective, emphasizing the connections between all forms of life.

accessible text Understanding stems from mak- ing connections between concepts and details, so a text with too little detail reads as a series of facts that beg to be memorized. However, excessive detail can overwhelm the introductory student. Thus, we con- stantly strive to strike the perfect balance between level of detail and accessibility. We once again revised the text to eliminate details that do not contribute to a basic understanding of essential concepts. We also know that English is a second language for many introductory students, so we avoid idioms and aim for a clear, straightforward style.

Analogies to familiar objects and phenomena will help students understand abstract concepts. For exam- ple, in the discussion of transpiration in Chapter 27 (Plant Form and Function), we explain that a column of water is drawn upward through xylem as a drinker draws fluid up through a straw.

in-text learning tools To emphasize connections between biological topics, each chapter begins with an application section that explores a current event or controversy directly related to the chapter’s content. For example, a discussion of binge drinking on col- lege campuses introduces the concept of metabolism in Chapter 4. This section presents an overview of the metabolic pathway that breaks down alcohol, linking the function of enzymes in the pathway to hangovers, alcoholism, and cirrhosis. The section is illustrated with a photo of a tailgate party that preceded a recent Notre Dame–Alabama football game, and also a photo of Gary Reinbach just before he died at age 22 of alcoholic liver disease. (In the index, you’ll find health-related applications denoted by red squares and environmental applications by green squares.)

To strengthen a student’s analytical skills and offer insight into contemporary research, each chapter includes an exercise called digging into data that is placed in a section with relevant content. The exer- cise consists of a short text passage—usually about a published scientific experiment—and a table, chart, or other graphic that presents experimental data. A student can use information in the text and graphic to answer a series of questions. For example, the exercise in Chapter 2 asks students to interpret results of a study that examined the effect of dietary fat intake on “good” and “bad” cholesterol levels.

The chapter itself consists of several numbered sections that contain a manageable chunk of informa- tion. Every section ends with a boxed take-home message in which we pose a question that reflects the critical content of the section, and then answer the question in bulleted list format. Every chapter has at least one figure it out question with an answer immediately following. These questions allow students to quickly check their understanding as they read. Mastering scientific vocabulary challenges many stu- dents, so we have included an on-page glossary of key terms introduced in each two-page spread, in addition to a complete glossary at the book’s end. The end-of-chapter material features a visual summary that reinforces each chapter’s key concepts. A self- quiz poses multiple choice and other short answer questions for self-assessment (answers are in Appen- dix I). A set of more challenging critical thinking questions provides thought-provoking exercises for the motivated student. The end matter of several chapters now includes a visual question that rein- forces learning in a nonverbal style.

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.

xiv PREFACE

design and Content revisions Throughout the book, text and art have been revised to help students grasp difficult concepts. The following list highlights some of the revisions to each chapter.

Introduction 1 Invitation to Biology Renewed and updated emphasis on the rel-

evance of new species discovery and the process of science.

Unit 1 How Cells work 2 Molecules of Life New graphic illustrates radioactive decay. 3 Cell Structure Application section updated with current statistics

and ‘pink slime’ story. Micrograph comparisons now feature Para- mecia and include a confocal image. Essay about the nature of life expanded to add Gerald Joyce’s “life is squishy” concept.

4 Energy and Metabolism Application section now illustrated with a real-life example. Diffusion illustrated with a tea bag in hot water.

5 Capturing and Releasing Energy Application section updated with current statistics and illustrated with a current photo of air pollu- tion in China. Yogurt production added to fermentation section.

Unit 2 Genetics 6 DNA Structure and Function Content reorganized: material on clon-

ing folded into Application section for concept connection, and chromosome structure now appears after DNA structure. New art demonstrates how replication errors become mutations.

7 Gene Expression and Control Ricin discussion revised to include medical applications. New material includes hairlessness mutation (in cats), evolution of lactose tolerance, heritability of DNA meth- ylations, telomeres.

8 How Cells Reproduce New material on telomeres, asexual vs. sexual mud snails. New micrograph shows multiple crossovers.

9 Patterns of Inheritance Epistasis is now illustrated with human skin color. New material about environmentally-triggered hemoglobin production in Daphnia; continuous variation in dog face length arising from short tandem repeats foreshadows DNA fingerprint- ing in chapter 10.

10 Biotechnology Updated coverage of personal genetic testing includes social impact of Angelina Jolie’s response to her test. New photos illustrate genetically modified animals. New “who’s the daddy” critical thinking question offers students an opportu- nity to analyze a paternity test based on SNPs.

Unit 3 Evolution and Diversity 11 Evidence of Evolution Photos of 19th century naturalists added

to emphasize the process of science that led to natural selection theory. How banded iron formations provide evidence of the evo- lution of photosynthesis added to fossil section. Plate tectonics art updated to reflect new evidence of lava lamp mantle movements.

12 Processes of Evolution New opening essay on resistance to anti- biotics as an outcome of agricultural overuse (warfarin material now exemplifies directional selection). New art illustrates founder effect, and hypothetical example in text replaced with reduced

diversity of ABO alleles in Native Americans. New art illustrates stasis in coelacanths.

13 Early Life Forms and the Viruses New introductory essay about study of the human microbiome, new coverage of Ebola, and new figure depicting mechanisms of gene exchange in prokaryotes.

14 Plants and Fungi Additional coverage of fungal ecology, including information about white-nose syndrome in bats.

15 Animal Evolution New introductory essay about invertebrates as a source of medicines. Updated information about Neanderthals and added coverage of the newly discovered Dennisovans.

Unit 4 Ecology 16 Population Ecology Updated coverage of human demographics. 17 Communities and Ecosystems New photos illustrate species interac-

tions; updated coverage of the increases in greenhouse gases. 18 The Biosphere and Human Effects New essay about dispersion of the

radioactive material released at Fukushima and new Digging Into Data about bioaccumulation of this material in tuna.

Unit 5 How Animals work 19 Animal Tissues and Organs Updated information about stem cell

research and tissue regeneration in animals. Improved figures depict epithelial and connective tissues.

20 How Animals Move New information about how different muscle fiber types relate to animal locomotion.

21 Circulation and Respiration Improved coverage of insect respiration, including a new photo.

22 Immunity New photos show skin as a surface barrier, a cytotoxic T cell killing a cancer cell, and victims of HIV. Immune response and lymphatic system illustrations updated.

23 Digestion and Excretion Revised essay about obesity and new com- parative information about the ruminant digestive system.

24 Neural Control and the Senses New opening essay about the effects of concussions. Discussion of the human nervous system has been reorganized. New information about echolocation.

25 Endocrine Control Opening essay now focuses on phthalates as endocrine disruptors. New Digging Into Data about BPA’s effect on insulin secretion.

26 Reproduction and Development Updated coverage of assisted repro- ductive technologies. Discussion of human reproductive structure and function has been reorganized.

Unit 6 How Plants work 27 Plant Form and Function Reorganization consolidates growth into a

separate section. Many new photos illustrate stem, leaf, and root structure(s). Material on fire scars added to dendroclimatology.

28 Plant Reproduction and Development Updates reflect current research on colony collapse and ongoing major breakthroughs in the field of plant hormone function. New photos illustrate fruit classification, asexual reproduction, early growth, ABA inhibition of seed germination, and tropisms.

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.

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We owe a special debt to the members of our advisory board, listed below. They helped us shape the book’s design and to choose appro priate content. We appreciate their guidance.

Andrew Baldwin, Mesa Community College Charlotte Borgeson, University of Nevada, Reno Gregory A. Dahlem, Northern Kentucky University Gregory Forbes, Grand Rapids Community College Hinrich Kaiser, Victor Valley Community College Lyn Koller, Pierce College Terry Richardson, University of North Alabama

We also wish to thank the reviewers listed below.

Idris Abdi, Lane College Meghan Andrikanich, Lorain County Community College Lena Ballard, Rock Valley College Barbara D. Boss, Keiser University, Sarasota Susan L. Bower, Pasadena City College James R. Bray Jr., Blackburn College Mimi Bres, Prince George’s Community College Randy Brewton, University of Tennessee Evelyn K. Bruce, University of North Alabama Steven G. Brumbaugh, Green River Community College Chantae M. Calhoun, Lawson State Community College Thomas F. Chubb, Villanova University Julie A. Clements, Keiser University, Melbourne Francisco Delgado, Pima Community College Elizabeth A. Desy, Southwest Minnesota State University Brian Dingmann, University of Minnesota, Crookston Josh Dobkins, Keiser University, online Hartmut Doebel, The George Washington University Pamela K. Elf, University of Minnesota, Crookston Johnny El-Rady, University of South Florida Patrick James Enderle, East Carolina University Jean Engohang-Ndong, BYU Hawaii Ted W. Fleming, Bradley University Edison R. Fowlks, Hampton University Martin Jose Garcia Ramos, Los Angeles City College J. Phil Gibson, University of Oklahoma Judith A. Guinan, Radford University Carla Guthridge, Cameron University Laura A. Houston, Northeast Lakeview–Alamo College Robert H. Inan, Inver Hills Community College Dianne Jennings, Virginia Commonwealth University Ross S. Johnson, Chicago State University Susannah B. Johnson Fulton, Shasta College Paul Kaseloo, Virginia State University Ronald R. Keiper, Valencia Community College West Dawn G. Keller, Hawkeye Community College Ruhul H. Kuddus, Utah Valley State College Dr. Kim Lackey, University of Alabama Vic Landrum, Washburn University Lisa Maranto, Prince George’s Community College Catarina Mata, Borough of Manhattan Community College Kevin C. McGarry, Keiser University, Melbourne Timothy Metz, Campbell University Ann J. Murkowski, North Seattle Community College Alexander E. Olvido, John Tyler Community College Joshua M. Parke, Community College of Southern Nevada Elena Pravosudova, Sierra College Nathan S. Reyna, Howard Payne University Carol Rhodes, Cañada College Todd A. Rimkus, Marymount University Laura H. Ritt, Burlington County College Lynette Rushton, South Puget Sound Community College Erik P. Scully, Towson University

Marilyn Shopper, Johnson County Community College Jennifer J. Skillen, Community College of Southern Nevada Jim Stegge, Rochester Community and Technical College Lisa M. Strain, Northeast Lakeview College Jo Ann Wilson, Florida Gulf Coast University

We were also fortunate to have conversations with the following workshop attendees. The insights they shared proved invaluable.

Robert Bailey, Central Michigan University Brian J. Baumgartner, Trinity Valley Community College Michael Bell, Richland College Lois Borek, Georgia State University Heidi Borgeas, University of Tampa Charlotte Borgenson, University of Nevada Denise Chung, Long Island University Sehoya Cotner, University of Minnesota Heather Collins, Greenville Technical College Joe Conner, Pasadena Community College Gregory A. Dahlem, Northern Kentucky University Juville Dario-Becker, Central Virginia Community College Jean DeSaix, University of North Carolina Carolyn Dodson, Chattanooga State Technical Community College Kathleen Duncan, Foothill College, California Dave Eakin, Eastern Kentucky University Lee Edwards, Greenville Technical College Linda Fergusson-Kolmes, Portland Community College Kathy Ferrell, Greenville Technical College April Ann Fong, Portland Community College Kendra Hill, South Dakota State University Adam W. Hrincevich, Louisiana State University David Huffman, Texas State University, San Marcos Peter Ingmire, San Francisco State Ross S. Johnson, Chicago State University Rose Jones, NW-Shoals Community College Thomas Justice, McLennan Community College Jerome Krueger, South Dakota State University Dean Kruse, Portland Community College Dale Lambert, Tarrant County College Debabrata Majumdar, Norfolk State University Vicki Martin, Appalachian State University Mary Mayhew, Gainesville State College Roy Mason, Mt. San Jacinto College Alexie McNerthney, Portland Community College Brenda Moore, Truman State University Alex Olvido, John Tyler Community College Molly Perry, Keiser University Michael Plotkin, Mt. San Jacinto College Amanda Poffinbarger, Eastern Illinois University Johanna Porter-Kelley, Winston-Salem State University Sarah Pugh, Shelton State Community College Larry A. Reichard, Metropolitan Community College Darryl Ritter, Okaloosa-Walton College Sharon Rogers, University of Las Vegas Lori Rose, Sam Houston State University Matthew Rowe, Sam Houston State University Cara Shillington, Eastern Michigan University Denise Signorelli, Community College of Southern Nevada Jennifer Skillen, Community College of Southern Nevada Jim Stegge, Rochester Community and Technical College Andrew Swanson, Manatee Community College Megan Thomas, University of Las Vegas Kip Thompson, Ozarks Technical Community College Steve White, Ozarks Technical Community College Virginia White, Riverside Community College Lawrence Williams, University of Houston Michael L. Womack, Macon State College

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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.

Today & Tomorrow

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acknowledgments

Writing, revising, and illustrating a biology text- book is a major undertaking for two full-time au- thors, but our efforts constitute only a small part of what is required to produce and distribute this one. We are truly fortunate to be part of a huge team of very talented people who are as commit- ted as we are to creating and disseminating an exceptional science education product.

Biology is not dogma; paradigm shifts are a common outcome of the fantastic amount of research in the field. Ideas about what material should be taught and how best to present that material to students changes from one year to the next. It is only with the ongoing input of our many academic reviewers and advisors (previous page) that we can continue to tailor this book to the needs of instructors and students while inte- grating new information and models. We con- tinue to learn from and be inspired by these dedicated educators.

On the production side of our team, the indis- pensable Grace Davidson orchestrated a continu- ous flow of files, photos, and illustrations while managing schedules, budgets, and whatever else happened to be on fire at the time. Grace, thank you as always for your patience and dedication. Thank you also to Cheryl DuBois, John Saranta- kis, and Christine Myaskovsky for your help with photoresearch. Copyeditor Anita Hueftle and proofreader Diane Miller, your valuable sugges- tions kept our text clear and concise.

Yolanda Cossio, thank you for continuing to support us and for encouraging our efforts to innovate and improve. Thanks also to Cengage Production Manager Hal Humphrey, Marketing Manager Tom Ziolkowski, and to Lauren Oliveira, who creates our exciting technology package, Associate Content Developers Casey Lozier and Kellie Petruzzelli, and Product Assistant Victor Luu.

Lisa Starr and Christine Evers, November 2014

Cengage learning testing Powered by Cognero is a flexible, online system that allows you to: • author, edit, and manage test bank content from

multiple Cengage Learning solutions • create multiple test versions in an instant • deliver tests from your LMS, your classroom, or

wherever you want

instructor Companion site Everything you need for your course in one place! This collection of book- specific lecture and class tools is available online via www.cengage.com/login. Access and download Power- Point presentations, images, instructor’s manual, videos, and more.

Cooperative learning Cooperative Learning: Making Connections in General Biology, 2nd Edi- tion, authored by Mimi Bres and Arnold Weisshaar, is a collection of separate, ready-to-use, short coop- erative activities that have broad application for first year biology courses. They fit perfectly with any style of instruction, whether in large lecture halls or flipped classrooms. The activities are designed to address a range of learning objectives such as reinforcing basic concepts, making connections between various chapters and top- ics, data analysis and graphing, developing problem solving skills, and mastering terminology. Since each activity is designed to stand alone, this collection can be used in a variety of courses and with any text.

mindtap A personalized, fully online digital learn- ing platform of authoritative content, assignments, and services that engages students with interactivity while also offering instructors their choice in the configuration of coursework and enhancement of the curriculum via web-apps known as MindApps. MindApps range from ReadSpeaker (which reads the text out loud to students) to Kaltura (which allows you to insert inline video and audio into your curriculum). MindTap is well beyond an eBook, a homework solution or digital supplement, a resource center website, a course delivery platform, or a Learning Management System. It is the first in a new category—the Personal Learning Experience.

New for this edition! MindTap has an integrated Study Guide, expanded quizzing and application activi- ties, and an integrated Test Bank.

aplia for Biology The Aplia system helps students learn key concepts via Aplia’s focused assignments and active learning opportunities that include randomized, automatically graded questions, exceptional text/art inte- gration, and immediate feedback. Aplia has a full course management system that can be used independently or in conjunction with other course management systems such as MindTap, D2L, or Blackboard.

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.

Today & Tomorrow

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Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.

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1.1 The Secret Life of Earth 4

1.2 Life Is More Than the Sum of Its Parts 4

1.3 How Living Things Are Alike 6

1.4 How Living Things Differ 8

1.5 The Science of Nature 11

1.6 The Nature of Science 16

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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.

4 INTroDucTIoN

1.1 The Secret Life of Earth In this era of detailed satellite imagery and cell phone global positioning systems, could there possibly be any places left on Earth that humans have not yet explored? Actually, there are plenty of them. In 2005, for example, helicopters dropped a team of scientists into the middle of a vast and otherwise inaccessible cloud forest atop New Guinea’s Foja Mountains. Within a few minutes, the explorers realized that their landing site, a dripping, moss-covered swamp, had been untouched by humans. Team member Bruce Beehler remarked, “Everywhere we looked, we saw amazing things we had never seen before. I was shouting. This trip was a once-in-a- lifetime series of shouting experiences.”

How did the explorers know they had landed in uncharted territory? For one thing, the forest was filled with plants and animals previously unknown even to native peoples that have long inhabited other parts of the region. During the next month, the team members discovered many new species, including a rhododendron plant with flowers the size of a plate and a frog the size of a pea. They also came across hundreds of species that are on the brink of extinction in other parts of the world, and some that supposedly had been extinct for decades. The animals had never learned to be afraid of humans, so they could easily be approached. A few were discovered as they casually wandered through campsites (Figure 1.1A).

New species are discovered all the time, often in places much more mundane than Indonesian cloud forests (Figure 1.1B). How do we know what species a par- ticular organism belongs to? What is a species, anyway, and why should discovering a new one matter to anyone other than a scientist? You will find the answers to such questions in this book. They are part of the scientific study of life, biology, which is one of many ways we humans try to make sense of the world around us.

Trying to understand the immense scope of life on Earth gives us some per- spective on where we fit into it. For example, hundreds of new species are discov- ered every year, but about 20 species become extinct every minute in rain forests alone—and those are only the ones we know about. The current rate of extinctions is about 1,000 times faster than normal, and human activities are responsible for the acceleration. At this rate, we will never know about most of the species that are alive on Earth today. Does that matter? Biologists think so. Whether or not we are aware of it, humans are intimately connected with the world around us. Our activities are profoundly changing the entire fabric of life on Earth. These changes are, in turn, affecting us in ways we are only beginning to understand.

Ironically, the more we learn about the natural world, the more we realize we have yet to learn. But don’t take our word for it. Find out what biologists know, and what they do not, and you will have a solid foundation upon which to base your own opinions about how humans fit into this world. By reading this book, you are choos- ing to learn about the human connection—your connection—with all life on Earth.

1.2 Life Is More Than the Sum of Its Parts What, exactly, is the property we call “life”? We may never actually come up with a good definition, because living things are too diverse, and they consist of the same basic components as nonliving things. When we try to define life, we end up with a long list of properties that differentiate living from nonliving things. These

Figure 1.1 Newly discovered species. Each of the thousands of species discovered every year is a reminder that we do not yet know all of the organ- isms living on our own planet. We don’t even know how many to look for. Information about the 1.8 million species we do know about is being collected in The Encyclopedia of Life, an online database maintained by collaborative effort (www.eol.org). (A) Tim Laman/National Geographic Stock; (B) Courtesy East Carolina University.

Application

A. Paul oliver discovered this tree frog perched on a sack of rice during a rainy campsite lunch in New Guinea’s Foja Mountains. The explorers dubbed the new species “Pinocchio frog” after the Disney character because the male frog’s long nose inflates and points upward during times of excitement.

B. Dr. Jason Bond holds a new species of trapdoor spider he discovered in sand dunes of california beaches in 2008. Bond named the spider Aptostichus stephencol- berti, after TV personality Stephen colbert.

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Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.

INVITATIoN To BIoLoGy ChApter 1 5

properties often emerge from the interactions of basic components. To understand how that works, take a look at these groups of squares:

A property called “roundness” emerges when the squares are organized one way, but not other ways. The idea that different structures can be assembled from the same basic building blocks is a recurring theme in our world, and also in biology.

Life has successive levels of organization, with new properties emerging at each level (Figure 1.2). This organization begins with interactions between atoms, which are fundamental units of matter—the building blocks of all substances

1

. Atoms bond together to form molecules

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. There are no atoms unique to living things, but there are unique molecules. In today’s natural world, only living things make the “molecules of life,” which are lipids, proteins, DNA, RNA, and complex carbohydrates. The emergent property of “life” appears at the next level, when many molecules of life become organized as a cell

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. A cell is the smallest unit of life. Cells survive and reproduce themselves using energy, raw materials, and information in their DNA.

Some cells live and reproduce independently; others do so as part of a mul- ticelled organism

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. An organism is an individual that consists of one or more cells. In most multicelled organisms, cells are organized as tissues, organs, and organ systems that interact to keep the body working properly.

A population is a group of interbreeding individuals of the same type, or spe- cies, living in a given area

5

. At the next level, a community consists of all popula- tions living in a given area

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. Communities may be large or small, depending on the area defined.

The next level of organization is the ecosystem, which is a community inter- acting with its physical and chemical environment

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. The most inclusive level, the biosphere, encompasses all regions of Earth’s crust, waters, and atmosphere in which organisms live

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.

Figure 1.2 Levels of organization in nature.

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Atoms are fundamental units of matter.

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Molecules consist of atoms.

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cells consist of molecules.

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organisms consist of cells.

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Populations consist of organisms.

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communities consist of populations.

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Ecosystems consist of communities interacting with their environment.

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The biosphere consists of all ecosystems on Earth.

Take-Home Message 1.2 how do living things differ from nonliving things?

• All things, living or not, consist of the same building blocks: atoms. Atoms bond together to form molecules.

• In today’s natural world, only living things make lipids, proteins, DNA, rNA, and com- plex carbohydrates. The unique properties of life emerge as these molecules become organized into cells.

• Higher levels of life’s organization include multicelled organisms, populations, com- munities, ecosystems, and the biosphere.

atom Fundamental building block of all matter.

biology The scientific study of life.

biosphere All regions of Earth where organisms live.

cell Smallest unit of life.

community All populations of all species in a given area.

ecosystem A community interacting with its environment.

molecule Two or more atoms bonded together.

organism Individual that consists of one or more cells.

population Group of interbreeding individuals of the same species that live in a given area.

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6 INTroDucTIoN

1.3 How Living Things Are Alike Even though we cannot precisely define “life,” we can intuitively understand what it means because all living things share a particular set of key features. All require ongoing inputs of energy and raw materials; all sense and respond to change; and all pass DNA to offspring.

Organisms Require Energy and Nutrients Not all living things eat, but all require energy and nutrients on an ongoing basis. Inputs of both are essential to maintain the functioning of individual organisms and the organization of life in general. A nutrient is a substance that an organism needs for growth and survival but cannot make for itself.

Organisms spend a lot of time acquiring energy and nutrients (Figure 1.3). However, the source of energy and the type of nutrients acquired differ among organisms. These differences allow us to classify living things into two catego- ries: producers and consumers. A producer makes its own food using energy and simple raw materials it obtains from nonbiological sources. Plants are producers; by a process called photosynthesis, they use the energy of sunlight to make sugars from water and carbon dioxide (a gas in air). Consumers, by contrast, cannot make their own food. A consumer obtains energy and nutrients by feeding on other organisms. Animals are consumers. So are decomposers, which feed on the wastes or remains of other organisms. The leftovers from consumers’ meals end up in the environment, where they serve as nutrients for producers. Said another way, nutri- ents cycle between producers and consumers.

Unlike nutrients, energy is not cycled. It flows through the world of life in one direction: from the environment, through organisms, and back to the environ- ment. This flow maintains the organization of every living cell and body, and it also influences how individuals interact with one another and their environment. The energy flow is one-way, because with each transfer, some energy escapes as heat, and cells cannot use heat as an energy source. Thus, energy that enters the world of life eventually leaves it (we return to this topic in Chapter 5).

Organisms Sense and Respond to Change An organism cannot survive for very long in a changing environment unless it adapts to the changes. Thus, every living thing has the ability to sense and respond to change both inside and outside of itself (Figure 1.4). Consider how, after you eat, the sugars from your meal enter your bloodstream. The added sugars set in motion a series of events that causes cells throughout the body to take up sugar faster, so the sugar level in your blood quickly falls. This response keeps your blood sugar level within a certain range, which in turn helps keep your cells alive and your body functioning properly.

All of the fluids outside of cells make up a body’s internal environment. That environment must be kept within certain ranges of temperature and other con- ditions, or the cells that make up the body will die. By sensing and adjusting to change, organisms keep conditions in the internal environment within a range that favors survival. Homeostasis is the name for this process, and it is one of the defin- ing features of life.

Organisms Grow and Reproduce With little variation, the same types of mol- ecules perform the same basic functions in every organism. For example, informa- tion in an organism’s DNA (deoxyribonucleic acid) guides ongoing functions that sustain the individual through its lifetime. Such functions include development:

Figure 1.3 the one-way flow of energy and the cycling of materials in the world of life. Top, © Victoria Pinder, www.flickr.com/photos/vixstarplus.

P R O D U C E R S plants and other self-feeding organisms

E N E R G Y I N S U N L I G H T

C O N S U M E R S animals, most fungi, many protists, bacteria

Producers harvest energy from the environment. Some of that energy flows from producers to consumers.

Nutrients that get incorporated into the cells

of producers and consumers are eventually released back into the environment (by decomposi-

tion, for example). Producers then take up some of the

released nutrients.

All energy that enters the world of life eventually flows out of it, mainly as heat released back to the environment.

consumer acquiring energy and nutrients by eating a producer

producer acquiring energy and nutrients from its environment

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INVITATIoN To BIoLoGy ChApter 1 7

DNA

Figure 1.4 Organisms sense and respond to stimulation. This baby orangutan is laughing in response to being tickled. Apes and humans make different sounds when being tickled, but the airflow patterns are so similar that we can say apes really do laugh. © Dr. Marina Davila Ross, University of Portsmouth.

consumer organism that gets energy and nutrients by feeding on the tissues, wastes, or remains of other organisms.

development Multistep process by which the first cell of a new multicelled organism gives rise to an adult.

DNA Deoxyribonucleic acid; carries hereditary infor- mation that guides development and other activities.

growth In multicelled species, an increase in the number, size, and volume of cells.

homeostasis Process in which an organism keeps its internal conditions within tolerable ranges by sensing and responding to change.

inheritance Transmission of DNA to offspring.

nutrient Substance that an organism needs for growth and survival but cannot make for itself.

photosynthesis Process by which a producer uses light energy to make sugars from carbon dioxide and water.

producer organism that makes its own food using energy and nonbiological raw materials from the environment.

reproduction Process by which parents produce offspring.

the process by which the first cell of a new individual becomes a multicelled adult; growth: increases in cell number, size, and volume; and reproduction: processes by which individuals produce offspring.

Individuals of every natural population are alike in certain aspects of their body form and behavior because their DNA is very similar: Orangutans look like orangutans and not like caterpillars because they inherited orangutan DNA, which differs from caterpillar DNA in the information it carries. Inheritance refers to the transmission of DNA to offspring. All organisms receive their DNA from one or more parents.

DNA is the basis of similarities in form and function among organisms. How- ever, the details of DNA molecules differ, and herein lies the source of life’s diversity. Small variations in the details of DNA’s structure give rise to differences among indi- viduals, and also among types of organisms. As you will see in later chapters, these differences are the raw material of evolutionary processes.

Take-Home Message 1.3 how are all living things alike?

• A one-way flow of energy and a cycling of nutrients sustain life’s organization. • organisms sense and respond to conditions inside and outside themselves. They

make adjustments that keep conditions in their internal environment within a range that favors cell survival, a process called homeostasis.

• All organisms use information in the DNA they inherited from their parent or parents to develop, grow, and reproduce. DNA is the basis of similarities and differences in form and function among organisms.

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Figure 1.5 A few representative prokaryotes. (A) top left, Dr. Richard Frankel; top right, Science Source; bottom left, www.zahnarzt-stuttgart .com; bottom right, © Susan Barnes; (B) left, Dr. Terry Beveridge, Visuals Unlimited/Corbis; right, © Dr. Harald Huber, Dr. Michael Hohn, Prof. Dr. K.O. Stetter, University of Regensburg, Germany.

A. Bacteria are the most numerous organisms on Earth. clockwise from upper left, a bacterium with a row of iron crystals that acts like a tiny compass; a common resident of cat and dog stomachs; spiral cyanobacteria; types found in dental plaque.

B. Archaea may resemble bacteria, but they are more closely related to eukaryotes. These are two types of archaea from a hydrothermal vent on the seafloor.

1.4 How Living Things Differ Living things differ tremendously in their observable characteristics. Various clas- sification schemes help us organize what we understand about the scope of this variation, which we call Earth’s biodiversity.

For example, organisms can be grouped on the basis of whether they have a nucleus, which is a saclike structure containing a cell’s DNA. Bacteria (singular, bacterium) and archaea (singular, archaeon) are organisms whose DNA is not contained within a nucleus. All bacteria and archaea are single-celled, which means each organism consists of one cell (Figure 1.5). Collectively, these organisms are the most diverse representatives of life. Different kinds are producers or consumers in nearly all regions of Earth. Some inhabit such extreme environments as frozen des- ert rocks, boiling sulfurous lakes, and nuclear reactor waste. The first cells on Earth may have faced similarly hostile conditions.

Traditionally, organisms without a nucleus have been called prokaryotes, but the designation is now used only informally. This is because, despite the similar appearance of bacteria and archaea, the two types of cells are less related to one another than we once thought. Archaea turned out to be more closely related to eukaryotes, which are organisms whose DNA is contained within a nucleus. Some eukaryotes live as individual cells; others are multicelled (Figure 1.6). Eukaryotic cells are typically larger and more complex than bacteria or archaea.

Protists are the simplest eukaryotes, but as a group they vary dramatically, from single-celled consumers to giant, multicelled producers.

Fungi (singular, fungus) are eukaryotic consumers that secrete substances to break down food externally, then absorb nutrients released by this process. Many fungi are decomposers. Most fungi, including those that form mushrooms, are mul- ticellular. Fungi that live as single cells are called yeasts.

Plants are multicelled eukaryotes, and the vast majority of them are photosyn- thetic producers that live on land. Besides feeding themselves, plants also serve as food for most other land-based organisms.

Animals are multicelled eukaryotic consumers that ingest tissues or juices of other organisms. Unlike fungi, animals break down food inside their body. They also develop through a series of stages that lead to the adult form. All animals actively move about during at least part of their lives.

What Is a Species? Each time we discover a new species, or unique kind of organism, we name it. Taxonomy, the practice of naming and classifying spe- cies, began thousands of years ago, but naming species in a consistent way did not become a priority until the eighteenth century. At the time, European explor- ers who were just discovering the scope of life’s diversity started having more and more trouble communicating with one another because species often had multiple names. For example, the dog rose (a plant native to Europe, Africa, and Asia) was alternately known as briar rose, witch’s briar, herb patience, sweet briar, wild briar, dog briar, dog berry, briar hip, eglantine gall, hep tree, hip fruit, hip rose, hip tree, hop fruit, and hogseed—and those are only the English names! Species often had multiple scientific names too, in Latin that was descriptive but often cumbersome. The scientific name of the dog rose was Rosa sylvestris inodora seu canina (odorless woodland dog rose), and also Rosa sylvestris alba cum rubore, folio glabro (pinkish white woodland rose with smooth leaves).

An eighteenth-century naturalist, Carolus Linnaeus, standardized a two-part naming system that we still use. By the Linnaean system, every species is given a

animal Multicelled consumer that develops through a series of stages and moves about during part or all of its life.

archaea Group of single-celled organisms that lack a nucleus but are more closely related to eukaryotes than to bacteria.

bacteria The most diverse and well-known group of single-celled organisms that lack a nucleus.

biodiversity Scope of variation among living organisms.

eukaryote organism whose cells characteristically have a nucleus.

fungus Single-celled or multicelled eukaryotic con- sumer that breaks down material outside itself, then absorbs nutrients released from the breakdown.

plant A multicelled, typically photosynthetic producer.

prokaryote Single-celled organism with no nucleus.

protists A group of diverse, simple eukaryotes.

species unique type of organism.

taxonomy Practice of naming and classifying species.

8

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INVITATIoN To BIoLoGy ChApter 1 9

Animals are multicelled con- sumers that ingest tissues or juices of other organisms. All actively move about during at least part of their life.

Fungi are eukaryotic consumers that secrete substances to break down food outside their body. Most are multicelled (left), but some are single-celled (above).

plants are multicelled eukaryotes. Almost all plants are photosynthetic producers, and most of them have roots, stems, and leaves.

protists are a group of extremely diverse eukary- otes that range from giant multicelled seaweeds to microscopic single cells.

Figure 1.6 A few representative eukaryotes. Protists: from left, © worldswildlifewonders/Shutterstock.com; top middle, Courtesy of Allen W. H. Bé and David A. Caron; bottom middle, © Emiliania Huxleyi photograph, Vita Pariente, scanning electron micrograph taken on a Jeol T330A instrument at Texas A&M University Electron Microscopy Center; top right, M I Walker/Science Source; middle right, © Carolina Biological Supply Company; bottom right, Oliver Meckes/Science Source; Plants: left, © Jag.ca.Shutterstock.com; right, © Martin Ruegner/Radius Images/Getty Images; Fungi, left, Edward S. Ross; right, London Scientific Films/Oxford Scientific/Getty Images; Animals: left, Shironina/Shutterstock.com; middle, © Martin Zimmerman, Science, 1961, 133:73–79, © AAAS; right, © Pixtal/SuperStock.

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10

unique two-part scientific name. The first part of a scientific name is the genus (plural, genera), a group of species that share a unique set of features. The second part is the specific epithet. Together, the genus name and the specific epithet desig- nate one species. Thus, the dog rose now has one official name, Rosa canina, that is recognized worldwide.

Genus and species names are always italicized. For example, Panthera is a genus of big cats. Lions belong to the species Panthera leo. Tigers belong to a different species in the same genus (Panthera tigris), and so do leopards (P. pardus). Note how the genus name may be abbreviated after it has been spelled out once.

A Rose by Any Other Name The individuals of a species share a unique set of inherited traits. For example, giraffes normally have very long necks, brown spots on white coats, and so on. These are morphological (structural) traits. Individuals of a species also share biochemical traits (they make and use the same molecules) and behavioral traits (they respond the same way to certain stimuli, as when hungry giraffes feed on tree leaves). We can rank species into ever more inclusive catego- ries based on some subset of traits it shares with other species. Each rank, or taxon (plural, taxa), is a group of organisms that share a unique set of traits. Each category above species—genus, family, order, class, phylum (plural, phyla), kingdom, and domain—consists of a group of the next lower taxon (Figure 1.7). Using this system, we can sort all life into a few categories (Figure 1.8).

It is easy to tell that orangutans and caterpillars are different species because they appear very different. Distinguishing between species that are more closely related may be much more challenging (Figure 1.9). In addition, traits shared by members of a species often vary a bit among individuals, as eye color does among

Figure 1.7 taxonomic classification of five species that are related at different levels. Each species has been assigned to ever more inclusive groups, or taxa: in this case, from genus to domain. From the left, Joaquim Gaspar; © kymkemp.com; Sylvie Bouchard/Shutterstock.com; Courtesy of Melissa S. Green, www.flickr.com/photos/henkimaa; © Grodana Sarkotic.

Answer: Marijuana, apple, prickly rose, and dog roseFigure It Out: Which of the plants shown here are in the same order?

domain kingdom phylum

class order

family genus

species

A “species” is a convenient but artificial construct of the human mind.

genus A group of species that share a unique set of traits.

taxon Group of organisms that share a unique set of traits.

Eukarya Plantae Magnoliophyta Magnoliopsida Apiales Apiaceae Daucus carota

wild carrot Eukarya Plantae Magnoliophyta Magnoliopsida rosales rosaceae Malus domestica

apple Eukarya Plantae Magnoliophyta Magnoliopsida rosales rosaceae Rosa acicularis

prickly rose Eukarya Plantae Magnoliophyta Magnoliopsida rosales rosaceae Rosa canina

dog rose Eukarya Plantae Magnoliophyta Magnoliopsida rosales cannabaceae Cannabis sativa

marijuana

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INVITATIoN To BIoLoGy ChApter 1 11

Bacteria Archaea Eukarya

B. Three-domain classification system. The Eukarya domain includes protists, plants, fungi, and animals.

Figure 1.9 Four butterflies, two species: Which are which? The top row shows two forms of the species Heliconius melpomene; the bottom row, two forms of H. erato.

H. melpomene and H. erato never cross-breed. Their alternate but similar patterns of coloration evolved as a shared warning signal to predatory birds that these but- terflies taste terrible. © 2006 Axel Meyer, “Repeating Patterns of Mimicry.” PLoS Biology Vol. 4, No. 10, e341 doi:10.1371/journal.pbio.0040341. Used with Permission.

Figure 1.8 two little ways to see the big picture of life. Lines in such diagrams indicate evolutionary connections.

people. How do we decide whether similar-looking organisms belong to the same species? The short answer to that question is that we rely on whatever information we have. Early naturalists studied anatomy and distribution—essentially the only methods available at the time—so species were named and classified according to what they looked like and where they lived. Today’s biologists are able to compare traits that the early naturalists did not even know about, including biochemical ones.

The discovery of new information sometimes changes the way we distinguish a particular species or how we group it with others. For example, Linnaeus grouped plants by the number and arrangement of reproductive parts, a scheme that resulted in odd pairings such as castor-oil plants with pine trees. Having more information today, we place these plants in separate phyla.

Evolutionary biologist Ernst Mayr defined a species as one or more groups of individuals that potentially can interbreed, produce fertile offspring, and do not interbreed with other groups. This “biological species concept” is useful in many cases, but it is not universally applicable. For example, we may never know whether two widely separated populations could interbreed if they got together. As another example, populations often continue to interbreed even as they diverge, so the exact moment at which two populations become two species is often impossible to pinpoint. We return to speciation and how it occurs in Chapter 12, but for now it is important to remember that a “species” is a convenient but artificial construct of the human mind.

1.5 The Science of Nature Most of us assume that we do our own thinking, but do we, really? You might be surprised to find out how often we let others think for us. Consider how a school’s job (which is to impart as much information to students as quickly as possible)

Take-Home Message 1.4 how do organisms differ from one another?

• organisms differ in their details; they show tremendous variation in observable characteristics.

• We divide Earth’s biodiversity into broad groups based on traits such as having a nucleus or being multicellular.

• Each species is given a unique, two-part scientific name. • classification systems group species on the basis of shared traits.

Bacteria Archaea FungiPlants AnimalsProtists

A. Six-kingdom classification system. The protist kingdom includes the most ancient multicelled and all single-celled eukaryotes.

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12

How do my own biases affect what I’m learning?

© JupiterImages Corporation.

meshes perfectly with a student’s job (which is to acquire as much knowledge as quickly as possible). In this rapid-fire exchange of information, it can be very easy to forget about the quality of what is being exchanged. Any time you accept informa- tion without questioning it, you let someone else think for you.

Thinking About Thinking Critical thinking is the deliberate process of judg- ing the quality of information before accepting it. “Critical” comes from the Greek kriticos (discerning judgment). When you use critical thinking, you move beyond the content of new information to consider supporting evidence, bias, and alterna- tive interpretations. How does the busy student manage this? Critical thinking does not necessarily require extra time, just a bit of extra awareness. There are many ways to do it. For example, you might ask yourself some of the following questions while you are learning something new:

What message am I being asked to accept? Is the message based on facts or opinion? Is there a different way to interpret the facts? What biases might the presenter have? How do my own biases affect what I’m learning?

Such questions are a way of being conscious about learning. They can help you decide whether to allow new information to guide your beliefs and actions.

How Science Works Critical thinking is a big part of science, the systematic study of the observable world and how it works. A scientific line of inquiry usually begins with curiosity about something observable, such as (for example) a decrease in the number of birds in a particular area. Typically, a scientist will read about what others have discovered before making a hypothesis, a testable explanation for a natural phenomenon. An example of a hypothesis would be, “The number of birds is decreasing because the number of cats is increasing.”

A prediction, or statement of some condition that should exist if the hypoth- esis is correct, comes next. Making predictions is often called the if–then process, in which the “if ” part is the hypothesis, and the “then” part is the prediction: If the number of birds is decreasing because the number of cats is increasing, then reduc- ing the number of cats should stop the decline.

Next, a researcher will test the prediction. Tests may be performed on a model, or analogous system, if working with an object or event directly is not possible. For

A. Studying the ecological benefits of weedy buffer zones on farms.

B. Measuring how much wood is produced by extremely old trees.

control group Group of individuals identical to an experimental group except for the independent vari- able under investigation.

critical thinking Evaluating information before accepting it.

data Experimental results.

experiment A test designed to support or falsify a prediction.

experimental group In an experiment, a group of individuals who have a certain characteristic or receive a certain treatment.

hypothesis Testable explanation of a natural phenomenon.

model Analogous system used for testing hypotheses.

prediction Statement, based on a hypothesis, about a condition that should exist if the hypothesis is correct.

science Systematic study of the observable world.

scientific method Making, testing, and evaluating hypotheses.

variable In an experiment, a characteristic or event that differs among individuals or over time.

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INVITATIoN To BIoLoGy ChApter 1 13

example, animal diseases are often used as models of similar human diseases. Care- ful observations are one way to test predictions that flow from a hypothesis. So are experiments: tests designed to support or falsify a prediction. A typical experiment explores a cause-and-effect relationship using variables, which are characteristics or events that can differ among individuals or over time.

Biological systems are typically complex, with many interdependent variables. It can be difficult to study one variable separately from the rest. Thus, biology researchers often test two groups of individuals simultaneously. An experimental group is a set of individuals that have a certain characteristic or receive a certain treatment. An experimental group is tested side by side with a control group, which is identical to the experimental group except for one independent variable: the characteristic or the treatment being tested. Any differences in experimental results between the two groups is likely to be an effect of changing the variable. Test results—data—that are consistent with the prediction are evidence in support of the hypothesis. Data inconsistent with the prediction are evidence that the hypothesis is flawed and should be revised.

A necessary part of science is reporting one’s results and conclusions in a stan- dard way, such as in a peer-reviewed journal article. The communication gives other scientists an opportunity to evaluate the information for themselves, both by check- ing the conclusions drawn and by repeating the experiments. Forming a hypothesis based on observation, and then systematically testing and evaluating the hypothesis, are collectively called the scientific method (Table 1.1).

Examples of Experiments in Biology There are many different ways to do research, particularly in biology (Figure 1.10). Some biologists survey, simply observing without making or testing hypotheses. Others make hypotheses based on observations, and leave the testing to others. However, despite a broad range of approaches, scientific experiments are typically designed in a consistent way, so the effects of changing one variable at a time can be measured. To give you a sense of how biology experiments work, we summarize two published studies here.

In 1996 the U.S. Food and Drug Administration (FDA) approved Olestra®, a fat replacement manufactured from sugar and vegetable oil, as a food additive. Potato chips were the first Olestra-containing food product to be sold in the United States. Controversy about the chip additive soon raged. Many people complained of intes- tinal problems after eating the chips, and thought that the Olestra was at fault. Two

table 1.1 the Scientific Method

observe some aspect of nature.

Think of an explanation for your observation (in other words, form a hypothesis).

Test the hypothesis. a. Make a prediction based on the hypothesis. b. Test the prediction using experiments or

surveys. c. Analyze the results of the tests (data).

Decide whether the results of the tests support your hypothesis or not (form a conclusion).

report your results to the scientific community.

Figure 1.10 A few examples of scientific research in the field of biology. (A) Photo by Scott Bauer, USDA/ARS; (B) MICHAEL NICHOLS/National Geographic Creative; (C) © Roger W. Winstead, NC State University; (D) National Cancer Institute; (E) Courtesy of Susanna López-Legentil.

e. Discovering medically active natural products made by marine animals.

C. Improving efficiency of biofuel production from agricultural waste.

D. Devising a vaccine that helps prevent cancer.

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14 INTroDucTIoN

years later, researchers at the Johns Hopkins University School of Medicine designed an experiment to test whether Olestra causes cramps. The researchers made the fol- lowing prediction: if Olestra causes cramps, then people who eat Olestra should be more likely to get cramps than people who do not eat it. To test the prediction, they used a Chicago theater as a “laboratory.” They asked 1,100 people between the ages of thirteen and thirty-eight to watch a movie and eat their fill of potato chips. Each person received an unmarked bag containing 13 ounces of chips. In this experiment, the individuals who received Olestra-laden potato chips were the experimental group, and the individuals who received regular chips were the control group.

A few days after the movie, the researchers contacted all of the people who participated in the experiment and collected any reports of post-movie gastrointes- tinal problems. Of 563 people making up the experimental group, 89 (15.8 percent) reported having cramps. However, so did 93 of the 529 people (17.6 percent) mak- ing up the control group—who had eaten the regular chips. People were about as likely to get cramps whether or not they ate chips made with Olestra. These results did not support the prediction, so the researchers concluded that eating Olestra does not cause cramps (Figure 1.11).

A different experiment that took place in 2005 investigated whether certain behaviors of peacock butterflies help the insects avoid predation by birds. The researchers performing this experiment began with two observations. First, when a peacock butterfly rests, it folds its wings, so only the dark underside shows (Fig- ure 1.12A). Second, when a butterfly sees a predator approaching, it repeatedly flicks its wings open, while also moving them in a way that produces a hissing sound and a series of clicks (Figure 1.12B).

The researchers were curious about why the peacock butterfly flicks its wings. After they reviewed earlier studies, they came up with two hypotheses that might explain the wing-flicking behavior.

Figure 1.11 the steps in a scientific experiment to determine whether Olestra causes intestinal cramps. A report of this study was published in the Journal of the American Medical Association in January 1998. Left, © Bob Jacobson/Corbis; background right, © SuperStock.

Eats regular potato chips

Eats Olestra potato chips

Olestra® causes intestinal cramps.

People who eat potato chips made with Olestra will be more likely to get intestinal cramps than those who eat potato chips made without Olestra.

89 of 563 people get cramps later (15.8%)

93 of 529 people get cramps later (17.6%)

Percentages are about equal. People who eat potato chips made with Olestra are just as likely to get intestinal cramps as those who eat potato chips made without Olestra. These results do not support the hypothesis.

Control Group Experimental Group

Hypothesis

Prediction

Experiment

Results

Conclusion

A

B

C

D

E

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INVITATIoN To BIoLoGy ChApter 1 15

1. Wing-flicking probably attracts predatory birds, but it also exposes brilliant spots that resemble owl eyes. Anything that looks like owl eyes is known to startle small, butterfly-eating birds, so exposing the wing spots might scare off predators.

2. The hissing and clicking sounds produced when the peacock butterfly moves its wings may be an additional defense that deters predatory birds.

The researchers then used their hypotheses to make the following predictions:

1. If exposing brilliant wing spots startles butterfly-eating birds, then peacock but- terflies missing their spots will be more likely to get eaten.

2. If hissing and clicking sounds deter birds butterfly-eating birds, then peacock butterflies unable to make these sounds will be more likely to get eaten.

The next step was the experiment. The researchers used a black marker to cover up the wing spots of some butterflies, and scissors to cut off the sound-making part of the wings of others. A third group had both treatments, their wings painted and also cut. The researchers then put each butterfly into a large cage with a hungry blue tit (Figure 1.12C) and watched the pair for thirty minutes.

Figure 1.12D lists the results of the experiment. All butterflies with unmodified wing spots survived, regardless of whether they made sounds. By contrast, only half of the butterflies that had spots painted out but could make sounds survived. Most

B. When a predatory bird approaches, a butterfly flicks its wings open and closed, reveal- ing brilliant spots and producing hissing and clicking sounds.

A. With wings folded, a resting peacock butterfly resembles a dead leaf, so it is appropriately camou- flaged from predatory birds.

C. researchers tested whether the wing-flicking behavior of peacock but- terflies affected predation by blue tits.

D. The researchers painted out the spots of some butterflies, cut the sound-making part of the wings on others, and did both to a third group; then exposed each butterfly to a hungry blue tit for 30 minutes. results are listed on the right.

experimental treatment

Number of Butterflies eaten (of total)

Spots painted out 5 of 10

Wings cut 0 of 8

Spots painted, wings cut 8 of 10

None 0 of 9

Figure 1.12 testing peacock butterfly defenses. (A) © Matt Rowlings, www.eurobutterflies.com; (B) © Adrian Vallin; (C) © Antje Schulte; (D) Proceedings of the Royal Society of London, Series B (2005) 272: 1203–1207.

Answer: 20 percent

Figure It Out: What percentage of butterflies with spots painted and wings cut survived the test?

Digging Into Data peacock Butterfly predator Defenses The photographs below represent the experimental and control groups used in the peacock butterfly experiment. Identify the experimental groups, and match them up with the relevant control group(s). Hint: Identify which variable is being tested in each group (each variable has a control). Adrian Vallin, Sven Jakobsson, Johan Lind and Christer Wiklund, Proc. R. Soc. B (2005: 272, 1203, 1207). Used with permission of The Royal Society and the author.

A. Wing spots painted out

B. Wing spots vis- ible; wings silenced

C. Wing spots painted out; wings silenced

D. Wings painted but spots visible

e. Wings cut but not silenced

F. Wings painted, spots visible; wings cut, not silenced

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16 INTroDucTIoN

of the silenced butterflies with painted-out spots were eaten quickly. The test results confirmed both predictions, so they support the hypotheses. Predatory birds are indeed deterred by peacock butterfly wing-flicking behavior.

1.6 The Nature of Science Bias in Interpreting Experimental Results Experimenting with a single vari- able apart from all others is not often possible, particularly when studying humans. For example, remember that the people who participated in the Olestra experiment were chosen randomly, which means the study was not controlled for gender, age, weight, medications taken, and so on. These variables may well have influenced the experiment’s results.

Humans are by nature subjective, and scientists are no exception. Research- ers risk interpreting their results in terms of what they want to find out. That is

Take-Home Message 1.5 how does science work?

• The scientific method consists of making, testing, and evaluating hypotheses. It is one way of critical thinking—systematically judging the quality of information before allowing it to guide one’s beliefs and actions.

• Natural processes are often very complex and influenced by many interacting variables.

• Experiments help researchers unravel causes of complex natural processes by focus- ing on the effects of changing a single variable.

Figure 1.13 example of how generalizing from a subset can lead to a conclusion that is incorrect. (A) Tim Laman/ National Geographic Stock; (B) © Bruce Beehler/ Conservation International.

B. In science, discov- ery of an error is not always bad news. Kris Helgen holds a golden- mantled tree kangaroo he found during the 2005 Foja Mountains survey. This kangaroo species is extremely rare in other areas, so it was thought to be criti- cally endangered prior to the expedition.

A. The cloud forest that covers about 2 million acres of New Guinea’s Foja Mountains is extremely remote and difficult to access, even for natives of the region. The first major survey of this forest occurred in 2005.

The scientific community consists of critically thinking people trying to poke holes in one another’s ideas.

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INVITATIoN To BIoLoGy ChApter 1 17

why they typically design experiments that will yield quantitative results, which are counts or some other data that can be measured or gathered objectively. Quantita- tive results minimize the potential for bias, and also give other scientists an oppor- tunity to repeat the experiments and check the conclusions drawn from them. This last point gets us back to the role of critical thinking in science. Scientists expect one another to recognize and put aside bias in order to test hypotheses in ways that may prove them wrong. If a scientist does not, then others will, because exposing errors is just as useful as applauding insights. The scientific community consists of critically thinking people trying to poke holes in one another’s ideas. Ideally, their collective efforts make science a self-correcting endeavor.

Sampling Error Researchers cannot always observe all individuals of a group. For example, the explorers you read about in Section 1.1 did not—and could not— survey every uninhabited part of the Foja Mountains. The cloud forest alone cloaks more than 2 million acres (Figure 1.13A), so surveying all of it would take unrealis- tic amounts of time and effort.

When researchers cannot directly observe all individuals of a population, all instances of an event, or some other aspect of nature, they may test or survey a subset. Results from the subset are then used to make generalizations about the whole. However, generalizing from a subset is risky because subsets are not neces- sarily representative of the whole. Consider the golden-mantled tree kangaroo, an animal first discovered in 1993 on a single forested mountaintop in New Guinea. For more than a decade, the species was never seen outside of that habitat, which is getting smaller every year because of human activities. Thus, the golden-mantled tree kangaroo was considered to be one of the most endangered animals on the planet. Then, in 2005, the New Guinea explorers discovered that this kangaroo spe- cies is fairly common in the Foja Mountain cloud forest (Figure 1.13B). As a result, biologists now believe its future is secure, at least for the moment.

Sampling error is a difference between results obtained from a subset, and results from the whole (Figure 1.14A). Sampling error may be unavoidable, but knowing how it can occur helps researchers design their experiments to minimize it. For example, sampling error can be a substantial problem with a small subset, so experimenters try to start with a relatively large sample, and they repeat their experiments (Figure 1.14B). To understand why these practices reduce the risk of sampling error, think about flipping a coin. There are two possible outcomes of each flip: The coin lands heads up, or it lands tails up. Thus, the chance that the coin will land heads up is one in two (1/2), or 50 percent. However, when you flip a coin repeatedly, it often lands heads up, or tails up, several times in a row. With just 3 flips, the proportion of times that the coin actually lands heads up may not even be close to 50 percent. With 1,000 flips, however, the overall proportion of times the coin lands heads up is much more likely to approach 50 percent.

Probability is the measure, expressed as a percentage, of the chance that a particular outcome will occur. That chance depends on the total number of pos- sible outcomes. For instance, if 10 million people enter a drawing, each has the same probability of winning: 1 in 10 million, or (an extremely improbable) 0.00001 per- cent. Analysis of experimental data often includes probability calculations. If there is a very low probability that a result has occurred by chance alone, the result is said to be statistically significant. In this context, the word “significant” does not refer to the result’s importance. Rather, it means that a rigorous statistical analysis has shown a very low probability (usually 5 percent or less) of the result being incorrect because of sampling error.

A. Natalie chooses a random jelly bean from a jar. She is blindfolded, so she does not know that the jar contains 120 green and 280 black jelly beans.

The jar is hidden from Natalie’s view before she removes her blindfold. She sees one green jelly bean in her hand and assumes that the jar must hold only green jelly beans. This assumption is incorrect: 30 percent of the jelly beans in the jar are green, and 70 percent are black. The small sample size has resulted in sampling error.

B. Still blindfolded, Natalie randomly chooses 50 jelly beans from the jar. She ends up choosing 10 green and 40 black beans.

The larger sample leads Natalie to assume that one- fifth of the jar’s jelly beans are green (20 percent) and four-fifths are black (80 percent). The larger sample more closely approximates the jar’s actual green-to- black ratio of 30 percent to 70 percent.

The more times Natalie repeats the sampling, the greater her chance of guessing the actual ratio.

Figure 1.14 how sample size affects sampling error. © Gary Head.

probability The chance that a particular outcome of an event will occur; depends on the total number of outcomes possible.

sampling error Difference between results derived from testing an entire group of events or individuals, and results derived from testing a subset of the group.

statistically significant refers to a result that is sta- tistically unlikely to have occurred by chance alone.

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18 INTroDucTIoN

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– spots + sound

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Variation in data is often shown as error bars on a graph (Figure 1.15). Depend- ing on the graph, error bars may indicate variation around an average for one sample set, or the difference between two sample sets.

Scientific Theories Suppose a hypothesis stands even after years of tests. It is consistent with all data ever gathered, and it has helped us make successful predic- tions about other phenomena. When a hypothesis meets these criteria, it is consid- ered to be a scientific theory (Table 1.2). To give an example, all observations to date have been consistent with the hypothesis that matter consists of atoms. Scien- tists no longer spend time testing this hypothesis for the compelling reason that, since we started looking 200 years ago, no one has discovered matter that consists of anything else. Thus, scientists use the hypothesis, now called atomic theory, to make other hypotheses about matter.

Scientific theories are our best objective descriptions of the natural world. How- ever, they can never be proven absolutely, because to do so would necessitate testing under every possible circumstance. For example, in order to prove atomic theory, the atomic composition of all matter in the universe would have to be checked—an impossible task even if someone wanted to try.

Like all hypotheses, a scientific theory can be disproven by a single observa- tion or result that is inconsistent with it. For example, if someone discovers a form of matter that does not consist of atoms, atomic theory would have to be revised. The potentially falsifiable nature of scientific theories means that science has a built-in system of checks and balances. A theory is revised until no one can prove it to be incorrect. The theory of evolution, which states that change occurs in a line of descent over time, still holds after a century of observations and testing. As with all other scientific theories, no one can be absolutely sure that it will hold under all possible conditions, but it has a very high probability of not being wrong. Few other theories have withstood as much scrutiny.

You may hear people apply the word “theory” to a speculative idea, as in the phrase “It’s just a theory.” This everyday usage of the word differs from the way it is used in science. Speculation is an opinion, belief, or personal conviction that is not necessarily supported by evidence. A scientific theory is different. By definition, a scientific theory is supported by a large body of evidence, and it is consistent with all known data.

A scientific theory also differs from a law of nature, which describes a phe- nomenon that has been observed to occur in every circumstance without fail, but for which we do not have a complete scientific explanation. The laws of

Science helps us communicate our experiences without bias.

Figure 1.15 example of error bars in a graph. This graph was adapted from the peacock butterfly research described in Section 1.5.

The researchers recorded the number of times each butterfly flicked its wings in response to an attack by a bird.

The squares represent average frequency of wing flicking for each sample set of butterflies. The error bars that extend above and below the dots indicate the range of values—the sampling error.

Answer: 22 times per minute

Figure It Out: What was the fastest rate at which a butterfly with no spots or sound flicked its wings?

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INVITATIoN To BIoLoGy ChApter 1 19

thermo dynamics, which describe energy, are examples. We understand how energy behaves, but not exactly why it behaves the way it does.

The Scope of Science Science helps us be objective about our observations in part because of its limitations. For example, science does not address many questions, such as “Why do I exist?” Answers to such questions can only come from within as an integration of the personal experiences and mental connections that shape our consciousness. This is not to say subjective answers have no value, because no human society can function for long unless its individuals share standards for making judgments, even if they are subjective. Moral, aesthetic, and philosophi- cal standards vary from one society to the next, but all help people decide what is important and good. All give meaning to our lives.

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