Biology For Dummies 2nd Edition PDF

g Eve ry thing Ea sier!™ 2nd Edition Makin Biology Learn to: Identify and dissect the many structures and functions of plants and animals Grasp the latest discoveries in evolutionary, reproductive, and ecological biology Think like a biologist and use scientific methods Rene Fester Kratz, PhD Author of Molecular and Cell Biology For Dummies Donna Rae Siegfried Writer and former college professor Get More and Do More at Dummies.com ® Start with FREE Cheat Sheets Cheat Sheets include Checklists Charts Common Instructions And Other Good Stuff! To access the Cheat Sheet created specifically for this book, go to www.dummies.com/cheatsheet/biology Get Smart at Dummies.com Dummies.com makes your life easier with 1,000s of answers on everything from removing wallpaper to using the latest version of Windows. Check out our Videos Illustrated Articles Step-by-Step Instructions Plus, each month you can win valuable prizes by entering our Dummies.com sweepstakes. * Want a weekly dose of Dummies? 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Biology FOR DUMmIES ‰ 2ND EDITION by Rene Fester Kratz, PhD, and Donna Rae Siegfried Biology For Dummies®, 2nd Edition Published by Wiley Publishing, Inc. 111 River St. Hoboken, NJ 07030-5774 www.wiley.com Copyright © 2010 by Wiley Publishing, Inc., Indianapolis, Indiana Published by Wiley Publishing, Inc., Indianapolis, Indiana Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permit- ted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600. 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Library of Congress Control Number: 2010926846 ISBN: 978-0-470-59875-7 Manufactured in the United States of America 10 9 8 7 6 5 4 3 2 1 About the Authors Rene Fester Kratz, PhD, teaches cellular biology and microbiology. She is a member of the North Cascades and Olympic Science Partnership, where she helped create inquiry-based science courses for future teachers. Kratz is also the author of Molecular and Cell Biology For Dummies and Microbiology The Easy Way. Donna Rae Siegfried has written about pharmaceutical and medical topics for 15 years in publications including Prevention, Runner’s World, Men’s Health, and Organic Gardening. She has taught anatomy and physiology at the college level. She is also the author of Anatomy & Physiology For Dummies. Dedication To the memory of Cindy Fuller Kratz Berdan, RN. Thanks for all of your encouragement over the years. —Rene Kratz Author’s Acknowledgments Thanks to Matt Wagner, of Fresh Books, Inc., for helping me (Rene) find the opportunity to work on the second edition of this book. And thanks to all the great people at Wiley who made it happen: editors Tim Gallan and Jennifer Tebbe, acquisitions editor Erin Calligan Mooney, art coordinator Alicia South, and technical reviewers Michael Pratt and Medhane Cumbay. Thanks also to Sheree Montgomery, the project coordinator in Composition, and Kathryn Born, who worked on the art. On the home front, thanks to my husband, Dan, and my sons, Hueston and Dashiel, for all of their love and support. —Rene Kratz Publisher’s Acknowledgments We’re proud of this book; please send us your comments through our Dummies online registration form located at http://dummies.custhelp.com. For other comments, please contact our Customer Care Department within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993, or fax 317-572-4002. Some of the people who helped bring this book to market include the following: Acquisitions, Editorial, and Media Composition Services Development Project Coordinator: Sheree Montgomery Senior Project Editor: Tim Gallan Illustrator: Kathryn Born Acquisitions Editor: Lindsay Lefevere Layout and Graphics: Ashley Chamberlain Copy Editor: Jennifer Tebbe Proofreaders: Laura Bowman, Lindsay Littrell Senior Editorial Assistant: David Lutton Indexer: Potomac Indexing, LLC Technical Editors: Medhane G. Cumbay, Michael W. Pratt Editorial Manager: Michelle Hacker Editorial Assistants: Jennette ElNaggar, Rachelle S. Amick Art Coordinator: Alicia B. South Cover Photos: © Digital Art/Corbis Cartoons: Rich Tennant (www.the5thwave.com) Publishing and Editorial for Consumer Dummies Diane Graves Steele, Vice President and Publisher, Consumer Dummies Kristin Ferguson-Wagstaffe, Product Development Director, Consumer Dummies Ensley Eikenburg, Associate Publisher, Travel Kelly Regan, Editorial Director, Travel Publishing for Technology Dummies Andy Cummings, Vice President and Publisher, Dummies Technology/General User Composition Services Debbie Stailey, Director of Composition Services Contents at a Glance Introduction................................................................ 1 Part I: Biology Basics.................................................. 7 Chapter 1: Exploring the Living World............................................................................ 9 Chapter 2: How Life Is Studied....................................................................................... 13 Chapter 3: The Chemistry of Life................................................................................... 27 Chapter 4: The Living Cell............................................................................................... 47 Chapter 5: Acquiring Energy to Run the Motor........................................................... 65 Part II: Cell Reproduction and Genetics: Let’s Talk about Sex, Baby......................................... 79 Chapter 6: Dividing to Conquer: Cell Division.............................................................. 81 Chapter 7: Making Mendel Proud: Understanding Genetics.................................... 101 Chapter 8: Reading the Book of Life: DNA and Proteins........................................... 113 Chapter 9: Engineering the Code: DNA Technology.................................................. 129 Part III: It’s a Small, Interconnected World............... 141 Chapter 10: Biodiversity and Classification............................................................... 143 Chapter 11: Observing How Organisms Get Along.................................................... 159 Chapter 12: Evolving Species in an Ever-Changing World........................................ 183 Part IV: Systems Galore! Animal Structure and Function........................................................... 203 Chapter 13: Pondering the Principles of Physiology................................................. 205 Chapter 14: Moving and Shaking: Skeletal and Muscular Systems.......................... 211 Chapter 15: Going with the Flow: Respiratory and Circulatory Systems............... 221 Chapter 16: Checking Out the Plumbing: Animal Digestive and Excretory Systems...................................................................................................... 241 Chapter 17: Fighting Back: Human Defenses.............................................................. 259 Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire... 277 Chapter 19: Reproduction 101: Making More Animals.............................................. 295 Part V: It’s Not Easy Being Green: Plant Structure and Function.................................... 319 Chapter 20: Living the Life of a Plant.......................................................................... 321 Chapter 21: Probing into Plant Physiology................................................................. 333 Part VI: The Par t of Tens.......................................... 341 Chapter 22: Ten Great Biology Discoveries................................................................ 343 Chapter 23: Ten Ways Biology Affects Your Life....................................................... 347 Index...................................................................... 351 Table of Contents Introduction................................................................. 1 About This Book.............................................................................................. 1 Conventions Used in This Book..................................................................... 2 What You’re Not to Read................................................................................ 2 Foolish Assumptions....................................................................................... 2 How This Book Is Organized.......................................................................... 3 Part I: Biology Basics............................................................................. 3 Part II: Cell Reproduction and Genetics: Let’s Talk about Sex, Baby................................................................ 3 Part III: It’s a Small, Interconnected World......................................... 4 Part IV: Systems Galore! Animal Structure and Function................. 4 Part V: It’s Not Easy Being Green: Plant Structure and Function.... 4 Part VI: The Part of Tens....................................................................... 5 Icons Used in This Book................................................................................. 5 Where to Go from Here................................................................................... 5 Part I: Biology Basics................................................... 7 Chapter 1: Exploring the Living World............................9 It All Starts with a Cell..................................................................................... 9 Life Begets Life: Reproduction and Genetics............................................. 10 Making the Connection between Ecosystems and Evolution.................. 11 Getting Up Close and Personal with the Anatomy and Physiology of Animals....................................................... 11 Comparing Plants to People......................................................................... 12 Chapter 2: How Life Is Studied..................................13 Living Things: Why Biologists Study Them and What Defines Them..... 13 Making Sense of the World through Observations................................... 15 Introducing the scientific method..................................................... 16 Designing experiments........................................................................ 18 Seeing Science as the Constant Sharing of New Ideas.............................. 22 Tracking Down Scientific Information......................................................... 24 Journals: Not just for recording dreams........................................... 24 Textbooks: A student’s go-to source................................................. 25 The popular press: Not always accurate.......................................... 25 The Internet: A wealth of information, not all of it good................ 25 x Biology For Dummies, 2nd Edition Chapter 3: The Chemistry of Life................................27 Exploring Why Matter Matters.................................................................... 27 Recognizing the Differences between Atoms, Elements, and Isotopes............................................................................. 28 “Bohr”ing you with atoms................................................................... 29 Elements of elements.......................................................................... 29 I so dig isotopes................................................................................... 32 Molecules, Compounds, and Bonds............................................................ 32 Acids and Bases (Not a Heavy Metal Band)............................................... 33 “Ph”iguring out the pH scale.............................................................. 34 Buffing up on buffers........................................................................... 35 Carbon-Based Molecules: The Basis for All Life........................................ 36 Providing energy: Carbohydrates...................................................... 36 Making life possible: Proteins............................................................ 39 Drawing the cellular road map: Nucleic acids................................. 41 Supplying structure, energy, and more: Lipids................................ 43 Chapter 4: The Living Cell......................................47 An Overview of Cells..................................................................................... 47 Peeking at Prokaryotes................................................................................. 49 Examining the Structure of Eukaryotic Cells............................................. 50 Cells and the Organelles: Not a Motown Doo-wop Group........................ 52 Holding it all together: The plasma membrane............................... 53 Supporting the cell: The cytoskeleton.............................................. 57 Controlling the show: The nucleus.................................................... 57 Creating proteins: Ribosomes............................................................ 58 Serving as the cell’s factory: The endoplasmic reticulum.............. 58 Preparing products for distribution: The Golgi apparatus............ 59 Cleaning up the trash: Lysosomes..................................................... 59 Destroying toxins: Peroxisomes........................................................ 59 Providing energy, ATP-style: Mitochondria..................................... 60 Converting energy: Chloroplasts....................................................... 60 Presenting Enzymes, the Jump-Starters..................................................... 61 Staying the same............................................................................... 62... while lowering activation energy................................................. 62 Getting some help from cofactors and coenzymes......................... 63 Controlling enzymes through feedback inhibition.......................... 63 Chapter 5: Acquiring Energy to Run the Motor....................65 What’s Energy Got to Do with It?................................................................. 65 Looking at the rules regarding energy.............................................. 66 Metabolizing molecules...................................................................... 67 Transferring energy with ATP............................................................ 67 Consuming food for matter and energy............................................ 68 Finding food versus producing your own......................................... 69 Table of Contents xi Photosynthesis: Using Sunlight, Carbon Dioxide, and Water to Make Food........................................................................... 70 Transforming energy from the ultimate energy source.................. 72 Putting matter and energy together.................................................. 72 Cellular Respiration: Using Oxygen to Break Down Food for Energy..... 73 Breaking down food............................................................................. 74 Transferring energy to ATP................................................................ 75 Energy and Your Body.................................................................................. 76 Part II: Cell Reproduction and Genetics: Let’s Talk about Sex, Baby:........................................ 79 Chapter 6: Dividing to Conquer: Cell Division.....................81 Reproduction: Keep On Keepin’ On............................................................ 81 Welcome to DNA Replication 101................................................................ 82 Cell Division: Out with the Old, In with the New....................................... 85 Interphase: Getting organized............................................................ 87 Mitosis: One for you, and one for you............................................... 88 Meiosis: It’s all about sex, baby......................................................... 91 How Sexual Reproduction Creates Genetic Variation.............................. 96 Mutations.............................................................................................. 96 Crossing-over....................................................................................... 96 Independent assortment..................................................................... 96 Fertilization........................................................................................... 97 Nondisjunction..................................................................................... 97 Pink and blue chromosomes.............................................................. 98 Chapter 7: Making Mendel Proud: Understanding Genetics.......101 Why You’re Unique: Heritable Traits and the Factors Affecting Them............................................................. 101 “Monk”ing Around with Peas: Mendel’s Laws of Inheritance................ 103 Pure breeding the parentals............................................................. 103 Analyzing the F1 and F2 generations............................................... 104 Reviewing Mendel’s results.............................................................. 104 Diving into the Pool of Genetic Terminology........................................... 105 Bearing Genetic Crosses............................................................................. 106 Studying Genetic Traits in Humans........................................................... 108 Creating pedigree charts.................................................................. 109 Testing different inheritance scenarios.......................................... 111 Drawing conclusions about traits.................................................... 112 xii Biology For Dummies, 2nd Edition Chapter 8: Reading the Book of Life: DNA and Proteins...........113 Proteins Make Traits Happen, and DNA Makes the Proteins................. 113 Moving from DNA to RNA to Protein: The Central Dogma of Molecular Biology............................................. 114 Rewriting DNA’s message: Transcription....................................... 115 Putting on the finishing touches: RNA processing........................ 118 Converting the code to the right language: Translation............... 119 Mistakes Happen: The Consequences of Mutation................................. 124 Giving Cells Some Control: Gene Regulation............................................ 126 Adapting to environmental changes............................................... 127 Becoming an expert through differentiation.................................. 127 Chapter 9: Engineering the Code: DNA Technology..............129 Understanding Just What’s Involved in DNA Technology...................... 130 Cutting DNA with restriction enzymes............................................ 130 Combining DNA from different sources.......................................... 131 Using gel electrophoresis to separate molecules.......................... 132 Copying a gene with PCR.................................................................. 133 Reading a gene with DNA sequencing............................................. 135 Mapping the Genes of Humanity............................................................... 135 Genetically Modifying Organisms.............................................................. 138 Why GMOs are beneficial.................................................................. 138 Why GMOs cause concern................................................................ 139 Part III: It’s a Small, Interconnected World................ 141 Chapter 10: Biodiversity and Classiﬁcation.....................143 Biodiversity: Recognizing How Our Differences Make Us Stronger...... 143 Valuing biodiversity.......................................................................... 144 Surveying the threats posed by human actions............................ 145 Exploring the extinction of species................................................. 146 Protecting biodiversity..................................................................... 147 Meet Your Neighbors: Looking at Life on Earth...................................... 148 Unsung heroes: Bacteria................................................................... 148 A bacteria impersonator: Archaeans.............................................. 149 A taste of the familiar: Eukaryotes................................................... 150 Climbing the Tree of Life: The Classification System of Living Things........................................................................................ 152 Mastering the domains...................................................................... 153 Organizing life into smaller and smaller groups............................ 154 Playing the name game..................................................................... 156 Table of Contents xiii Chapter 11: Observing How Organisms Get Along................159 Ecosystems Bring It All Together.............................................................. 159 Biomes: Communities of life............................................................. 160 Why can’t we be friends: Interactions between species............... 162 Studying Populations Is Popular in Ecology............................................ 163 Reviewing the basic concepts of population ecology................... 163 Discovering how populations grow................................................. 167 Taking a closer look at the human population.............................. 170 Moving Energy and Matter around within Ecosystems.......................... 173 Going with the (energy) flow............................................................ 175 Cycling matter through ecosystems............................................... 178 Chapter 12: Evolving Species in an Ever-Changing World.........183 What People Used to Believe..................................................................... 183 How Charles Darwin Challenged Age-Old Beliefs about Life on Earth.................................................................................. 185 Owing it all to the birds..................................................................... 185 Darwin’s theory of biological evolution.......................................... 186 The idea of natural selection............................................................ 186 The Evidence of Biological Evolution....................................................... 190 Biochemistry...................................................................................... 190 Comparative anatomy....................................................................... 191 Geographic distribution of species................................................. 191 Molecular biology.............................................................................. 193 Fossil record....................................................................................... 193 Observable data................................................................................. 194 Radioisotope dating........................................................................... 195 Why So Controversial? Evolution versus Creationism........................... 195 How Humans Evolved................................................................................. 197 Fossil finds.......................................................................................... 198 Digging into DNA................................................................................ 201 Check out the big brain on the Homo sapien................................. 201 Part IV: Systems Galore! Animal Structure and Function............................................................ 203 Chapter 13: Pondering the Principles of Physiology..............205 Studying Function at All Levels of Life...................................................... 205 Wrapping Your Head around the Big Physiological Ideas..................... 207 Evolving the perfect form................................................................. 207 Balancing the body to maintain homeostasis................................ 208 Getting the message across plasma membranes........................... 209 Recognizing that what comes in, must go out............................... 210 xiv Biology For Dummies, 2nd Edition Chapter 14: Moving and Shaking: Skeletal and Muscular Systems...........................................211 Doing the Locomotion, Animal-Style......................................................... 211 The Types of Skeletal Systems................................................................... 212 Splitting apart vertebrate skeletons................................................ 212 Boning up on bones........................................................................... 213 Joining the movement fun................................................................ 215 Why Muscles Are So Essential................................................................... 215 Muscle tissue and physiology.......................................................... 216 Muscle contraction............................................................................ 218 Chapter 15: Going with the Flow: Respiratory and Circulatory Systems......................................221 Passing Gas: How Animals “Breathe”........................................................ 221 Integumentary exchange................................................................... 222 Gills...................................................................................................... 223 Tracheal exchange systems............................................................. 223 Lungs................................................................................................... 224 Circulation: Nutrients In, Garbage Out..................................................... 227 Open circulatory systems................................................................. 227 Closed circulatory systems.............................................................. 228 Getting to the Heart of Simpler Animals................................................... 228 A worm’s heart and circulatory system.......................................... 229 A fish’s heart and circulatory system............................................. 229 Exploring the Human Heart and Circulatory System.............................. 230 Entering the cardiac cycle................................................................ 233 Navigating the path of blood through the body............................ 234 Seeing what makes your ticker tick................................................. 236 A Bloody-Important Fluid........................................................................... 237 The solids found in your essential fluid.......................................... 237 The plasma “stream” in your bloodstream.................................... 239 How blood clots form........................................................................ 239 Chapter 16: Checking Out the Plumbing: Animal Digestive and Excretory Systems.......................241 Obtaining Food and Breaking It Down...................................................... 241 The Ins and Outs of Digestive Systems..................................................... 243 Incomplete versus complete digestive tracts................................ 243 Continuous versus discontinuous feeders..................................... 243 Traveling through the Human Digestive System..................................... 244 The busiest stop of all — your mouth............................................ 245 The inner workings of your stomach.............................................. 245 The long and winding road of your small intestine....................... 246 Absorbing the Stuff Your Body Needs...................................................... 247 How nutrients travel through your body........................................ 248 Glucose regulation............................................................................. 248 Table of Contents xv What’s for Dinner? Making Wise, Nutritious Food Choices................... 249 Carbohydrates: The culprits of your food cravings...................... 250 Proteins: You break down their chains; they build yours............ 250 Fats: You need some, but don’t overdo it....................................... 252 Minerals and vitamins: The fuel for your enzymes....................... 253 Exploring the Human Excretory System................................................... 254 Getting to know your large intestine and how it eliminates solid wastes...................................................... 254 Flowing through how your kidneys remove nitrogenous wastes........................................................................ 255 Chapter 17: Fighting Back: Human Defenses....................259 Microbial Encounters of the Best and Worst Kinds................................ 259 Good bacteria: Health helpers......................................................... 260 Bad bacteria: Health harmers.......................................................... 260 Viruses: All bad, all the time............................................................. 261 Built to Protect You: Innate Human Defenses.......................................... 262 Your body’s best blockers: Skin and mucous membranes.......... 263 Tiny but mighty: Molecular defenders............................................ 264 Microbe seeker-outers: Dendritic cells........................................... 265 Invader eaters, big and small: Phagocytes..................................... 266 Damage control: Inflammation......................................................... 266 A fluid filterer: The lymphatic system............................................. 267 Learning a Lesson: Adaptive Human Defenses........................................ 268 Commanders-in-chief: Helper T cells.............................................. 269 Soldiers on the march: B cells and antibodies............................... 270 Cellular assassins: Cytotoxic T cells............................................... 270 Giving Your Defenses a Helping Hand...................................................... 271 Killing bacteria with antibiotics....................................................... 271 Using viruses to kill bad bacteria.................................................... 272 Fighting viruses with antiviral drugs............................................... 273 Getting ahead of the game with vaccines....................................... 273 Aging and Ailing: Changes in the Immune System.................................. 275 Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire...................................277 The Many Intricacies of Nervous Systems............................................... 277 Distinguishing between the CNS and PNS...................................... 278 Branching out to study neuron structure....................................... 280 Processing signals with the three types of neurons..................... 281 Acting without thinking..................................................................... 281 What a Sensation! The Brain and the Five Senses................................... 282 Oooh, that smell: Olfaction............................................................... 283 Mmm, mmm, good: Taste................................................................. 284 Now hear this: Sound........................................................................ 285 Seeing is believing: Sight................................................................... 285 A touchy-feely subject: Touch.......................................................... 286 xvi Biology For Dummies, 2nd Edition Following the Path of Nerve Impulses...................................................... 287 Traveling from one end to the other............................................... 287 Jumping the gap between neurons.................................................. 289 The Endocrine System: All Hormones Are Not Raging........................... 291 Seeing how hormones work............................................................. 292 Surveying the general functions of hormones............................... 293 Chapter 19: Reproduction 101: Making More Animals............295 This Budding’s for You: Asexual Reproduction...................................... 295 The Ins and Outs of Sexual Reproduction................................................ 296 Getting to know gametes.................................................................. 297 Mating rituals and other preparations for the big event.............. 299 How humans mate............................................................................. 304 How Other Animals Do It............................................................................ 307 Developing New Humans............................................................................ 309 From single cells to blastocyst......................................................... 309 Go, go, embryo................................................................................... 311 Fetal development and birth............................................................ 312 Differentiation, Development, and Determination.................................. 313 The ability to become any type of cell............................................ 314 The factors that affect differentiation and development.............. 315 Gender differentiation in humans.................................................... 316 Part V: It’s Not Easy Being Green: Plant Structure and Function..................................... 319 Chapter 20: Living the Life of a Plant...........................321 Presenting Plant Structure......................................................................... 321 Plant tissues....................................................................................... 322 The types of plants............................................................................ 322 Herbaceous versus woody stems.................................................... 324 Obtaining Matter and Energy for Growth................................................. 326 Going It Alone: Asexual Reproduction...................................................... 327 Mixing Sperm and Eggs: Sexual Reproduction........................................ 328 The life of a plant............................................................................... 328 The parts of a flower......................................................................... 330 How pollination and fertilization occur.......................................... 330 From zygote to embryo..................................................................... 332 A little protection for the embryo: Seeds....................................... 332 Chapter 21: Probing into Plant Physiology......................333 How Nutrients, Fluids, and Sugars Move through Plants....................... 333 Taking an inventory of the nutrients plants need to survive....... 334 Transporting water and other nutrients from the ground up...... 336 Table of Contents xvii Translocating sugars upward and downward through the phloem................................................... 337 Controlling water loss....................................................................... 338 Sending Signals with Plant Hormones...................................................... 340 Part VI: The Par t of Tens........................................... 341 Chapter 22: Ten Great Biology Discoveries......................343 Seeing the Unseen....................................................................................... 343 Creating Penicillin, the First Antibiotic..................................................... 343 Protecting People from Smallpox.............................................................. 344 Defining DNA Structure............................................................................... 344 Finding and Fighting Defective Genes....................................................... 344 Discovering Modern Genetic Principles................................................... 345 Evolving the Theory of Natural Selection................................................. 345 Formulating Cell Theory............................................................................. 345 Moving Energy through the Krebs Cycle.................................................. 346 Amplifying DNA with PCR........................................................................... 346 Chapter 23: Ten Ways Biology Affects Your Life.................347 Keeping You Fed.......................................................................................... 347 Putting Microbial Enzymes to Work.......................................................... 347 Designing Genes........................................................................................... 348 Obtaining Fossil Fuels for Energy.............................................................. 348 Causing and Treating Infectious Disease.................................................. 348 Staying Alive................................................................................................. 349 Providing You with Clean Water............................................................... 349 Changing Physically and Mentally............................................................. 349 Creating Antibiotic-Resistant Bacteria...................................................... 350 Facing Extinction......................................................................................... 350 Index....................................................................... 351 xviii Biology For Dummies, 2nd Edition Introduction L ife is all around you, from invisible microbes and green plants to the other animals with whom you share the Earth. What’s more, these other living things aren’t just around you — they’re intimately interconnected with your life. Plants make your food and provide you with oxygen, microbes break down dead matter and recycle materials that all living things need, and insects pollinate the plants you rely on for food. Ultimately, all living beings rely on other living beings for their survival. What makes biology so great is that it allows you to explore the interconnect- edness of the world’s organisms and really understand that living beings are works of art and machines rolled into one. Organisms can be as delicate as a mountain wildflower or as awe-inspiring as a majestic lion. And regardless of whether they’re plants, animals, or microbes, all living things have numerous working parts that contribute to the function of the whole being. They move, obtain energy, use raw materials, and make waste, whether they’re as simple as a single-celled organism or as complex as a human being. Biology is the key you need to unlock the mysteries of life. Through it, you discover that even single-celled organisms have their complexities, from their unique structures to their diverse metabolisms. Biology also helps you realize what a truly miraculous machine your body is, with its many different systems that work together to move materials, support your structure, send signals, defend you from invaders, and obtain the matter and energy you need for growth. About This Book Biology For Dummies, 2nd Edition, takes a look at the characteristics all living things share. It also provides an overview of the concepts and processes that are fundamental to living things. We put an emphasis on looking at how human beings meet their needs, but we also take a look at the diversity of life on planet Earth. 2 Biology For Dummies, 2nd Edition Conventions Used in This Book To help you find your way through the subjects in this book, we use the fol- lowing style conventions: ✓ Italics highlight new words or terms that are defined in the text. They also point out words we want to emphasize. ✓ Boldface indicates key words in bulleted lists or the action parts of num- bered steps. ✓ Monofont points out Web addresses so you can recognize them easily. ✓ Sidebars are gray-shaded boxes that contain text that’s interesting to know but not necessarily critical to your understanding of the chapter or section topic. Also, whenever we introduce scientific terms, we try to break the words down for you so that the terms become tied to their meanings, making them easier to remember. What You’re Not to Read Throughout this book you’ll find paragraphs marked with a Technical Stuff icon and sidebars (gray-shaded boxes). The Technical Stuff paragraphs provide more in-depth explanation of a topic or concept, and the sidebars include stories or information related to the main topic. They’re fun to read, but they’re by no means necessary for a thorough understanding of biology. So skip over them if you want to or read them to your heart’s content — the choice is yours! Foolish Assumptions As we wrote this book, we tried to imagine who you are and what you need in order to understand biology. Here’s what we came up with: ✓ You’re a high school student taking biology, possibly in preparation for an advanced placement test or college entrance examination. If you’re having trouble in biology class and your textbook isn’t making much sense, try reading the relevant section of this book first to give yourself a foundation and then go back to your textbook or notes. ✓ You’re a college student who isn’t a science major but is taking a biology class to help fulfill your degree requirements. If you want help following along in class, try reading the relevant sections in this book before you Introduction 3 go to a lecture on a particular topic. If you need to fix a concept in your brain, read the related section after class. ✓ You’re someone who just wants to know a little bit more about the living world around you. Good news... this book is your oyster! Read it at your leisure, starting with whatever topic fascinates you most. We include several examples of how biology impacts everyday life to help keep your interest piqued. How This Book Is Organized Biology For Dummies, 2nd Edition, is organized so that it mirrors the order of topics covered in a typical biology class. Like all For Dummies books, each chapter is self-contained, so you can pick up this book whenever you need it and jump straight into the topic you’re working on. Note: After we explain a subject, we use that information in later topics. If you don’t read the book in order, you may occasionally have to refer back to an earlier section for some background information. When that’s the case, we refer you to the appropriate chapter. Part I: Biology Basics If biology is the study of life and life is so complex, then you may be wonder- ing where to even begin in your study of biology. Never fear. This part breaks down the all-encompassing field of biology into smaller, more palatable chunks. First, we take a look at the living world and then explain exactly how biology is studied (hint: the scientific method is a huge part of it). Next, we give you a review of the types of molecules that are important to a cell’s functioning (yes, this means delving into some basic chemistry; sorry!). Then we spot- light the most basic unit of life — the cell. Every organism, whether it’s a human, a dog, a flower, a strep throat bacterium, or an amoeba, has at least one cell (most actually have millions). Finally, because cells need energy to function, we explain just where that energy comes from. Part II: Cell Reproduction and Genetics: Let’s Talk about Sex, Baby How do you get a multicellular human from a one-celled embryo? Cellular reproduction, of course! Cells can make exact copies of themselves in order 4 Biology For Dummies, 2nd Edition to repair, grow, or produce offspring that are genetically identical to the parent cell. You find out all about that in this part, as well as how some organisms mix things up by engaging in sexual reproduction, creating off- spring that have combinations of genes that are different from those of their parents. Regardless of whether organisms reproduce asexually or sexually, the traits of the parents are visible in the offspring because parents pass DNA on to their offspring. As you discover in this part, DNA contains the blueprints for proteins that do the work in cells and thus determine the characteristics of the offspring. Part III: It’s a Small, Interconnected World All the amazingly diverse forms of life on Earth interact with each other (if they didn’t, life on this planet would be in big trouble). This part allows you to explore all the ways life on Earth is connected, as well as how biologists classify organisms. You also get to discover how yesterday’s living beings are connected to today’s living beings through biological evolution. Part IV: Systems Galore! Animal Structure and Function Organisms respond to changes in their environment, trying to maintain their internal conditions within a range that supports life. Animals have many dif- ferent systems designed to support this struggle for balance. In this part of the book, we present most of the systems that support the structure and function of the human body, as well as those of other animals. These systems coordinate many functions in animals, such as digestion, movement, circula- tion, gas exchange, and defense. Part V: It’s Not Easy Being Green: Plant Structure and Function Plants, your green neighbors, often get overlooked in the hustle and bustle of animal life. However, the importance of plants to life on Earth simply can’t be overstated. After all, without them, you wouldn’t have any food. When you take the time to study plants, you find that they’re actually pretty interesting. Just like animals, they’re made of cells and have systems to transport materi- als around their bodies and exchange matter and energy with their environ- ment, all of which you find out in this part. Introduction 5 Part VI: The Part of Tens No For Dummies book would be complete without The Part of Tens and its chapters containing fun and interesting facts. When you venture to this part, prepare to find out about ten great biology discoveries and ten ways biology affects your life. Icons Used in This Book We use some of the familiar For Dummies icons to help guide you and give you new insights as you read the material. Here’s the scoop on what each one means. The information highlighted with this icon is stuff we think you should perma- nently store in your mental biology file. If you want a quick review of biology, scan through the book reading only the paragraphs marked with Remember icons. Next to these icons lie paragraphs that give you extra information but aren’t necessary to understanding the material in the chapter. If you want to take your understanding of biology to a higher level, or if you just want to build your knowledge base of interesting facts, incorporate these para- graphs into your reading. If you just want the basics and don’t want to bother with nonessential information, skip them. This bull’s-eye symbol offers pointers that help you remember the facts pre- sented in a particular section so you can better commit them to memory. Where to Go from Here Where you start reading is up to you. However, we do have a few suggestions: ✓ If you’re currently in a biology class and having trouble with a particular topic, jump right to the chapter or section featuring the subject that’s confusing you. ✓ If you’re using this book as a companion to a biology class that’s just beginning, you can follow along with the topics being discussed in class with one small exception. Many biology classes work from the smallest to the largest, beginning with molecules and then moving on to cells. We prefer to start with cells to give you an idea of where everything is hap- pening before moving on to the molecules. Whatever your situation, the table of contents and index can help you find the information you need. 6 Biology For Dummies, 2nd Edition Part I Biology Basics In this part... B iology is the study of living things — how they reproduce, how they change and respond to the environment, and how they obtain the energy and matter they need to grow. One goal of this part is to immerse you in the world of biology so you can understand how biolo- gists go about studying living things and know what chem- ical components make up all forms of life. Living things with many cells, like you, are made up of organ systems, organs, tissues, and cells. Cells are the smallest entities that show all the properties of life, so that’s where we begin zeroing in on things. The other goal of this part is to acquaint you with the structure of cells and how they obtain the energy they need to function. Chapter 1 Exploring the Living World In This Chapter ▶ Seeing how cells are part of all living things ▶ Finding out the fundamentals of where babies come from and why you have the traits you do ▶ Recognizing that all of Earth’s ecosystems are interconnected ▶ Surveying animal anatomy and physiology ▶ Exploring the similarities and differences between plants and people B iology is the study of life, as in the life that covers the surface of the Earth like a living blanket, filling every nook and cranny from dark caves and dry deserts to blue oceans and lush rain forests. Living things interact with all of these environments and each other, forming complex, interconnected webs of life. For many people, a hike in the forest or a trip to the beach is a chance to reconnect with the natural world and enjoy the beauty of life. In this chapter, we give you an overview of the big concepts of biology. Our goal is to show you how biology connects to your life and to give you a pre- view of the topics we explore in greater detail later in this book. It All Starts with a Cell Quick. What’s the smallest unit of life you can think of? (Here’s a hint: Try to recall the basic properties of life; if you can’t, head to Chapter 2 to discover what they are.) Your mind may automatically call up images of ants, amoe- bas, or bacteria, but that’s not quite the answer. The absolute smallest unit of life is a single cell. Everything an organism’s body does happens because its cells make those actions happen, whether that organism is a single-celled E. coli bacteria or a human being made up of approximately 10 trillion cells. 10 Part I: Biology Basics Of course, the number of cells you have isn’t the only difference between you and E. coli. The structure of your cells is a little bit different — your cells have more specialized internal compartments, such as the nucleus that houses your DNA (we cover cell structure in Chapter 4). Yet you have some distinct similarities as well. Both you and E. coli are made up of the same raw materials (flip to Chapter 3 to find out what those are) and have DNA as your genetic material (more on DNA in Chapter 8). You also use food the same way (see Chapter 5), and you build your proteins in the same manner (see Chapter 8). Life Begets Life: Reproduction and Genetics You began life as a single cell, when a sperm cell from your dad met an egg cell from your mom. Your parents made these reproductive cells through a special type of cell division called meiosis (we explain meiosis in detail in Chapter 6). When their reproductive cells combined, your dad and mom each donated half of your genetic information — 23 chromosomes from mom and 23 from dad — for a total of 46 chromosomes in each of your cells. The genes on those 46 chromosomes determined your characteristics, from your physi- cal appearance to much of your behavior. The science of genetics tracks the inheritance of genes and studies how they determine traits (see Chapter 7). Through genetics, you can understand why your skin is a certain color or why some traits seem to run in your family. Your genes are found in your DNA, which is in turn found in your chromo- somes. Each chromosome consists of hundreds of different blueprints that contain the instructions for your cells’ worker molecules (which are mostly proteins). Each type of cell in your body uses the blueprints found in your genes to build the proteins it needs to do its particular job. So what exactly does all that mean? Here it is, plain and simple: DNA determines your traits because it contains the instructions for the worker molecules (proteins) that make your traits happen. Scientists are discovering more and more about DNA; they’re also developing tools to read and alter the DNA in cells (see Chapter 9). Chances are you’re already experiencing the impacts of scientists’ work with DNA, even if you don’t know it. Why? Because scientists use recombinant DNA technology to alter organisms used in food and medicines. This technology allows them to take genes from one organism and place them into the cells of another, changing the characteristics of the receiving organism. For example, scien- tists alter the cells of bacteria with human genes, turning them into tiny living factories that produce human proteins needed to treat diseases. Chapter 1: Exploring the Living World 11 Making the Connection between Ecosystems and Evolution As you discover in Chapter 10, the amazing diversity of life on Earth helps ensure that life continues in the face of environmental change. Each type of organism plays a role in the environment, and each one is connected to the other. Green organisms such as plants combine energy and matter to make the food on which all life depends, predators hunt prey, and decomposers such as bacteria and fungi recycle dead matter so it becomes available again to other living things. (For more on the interconnectedness of all living things on Earth, head to Chapter 11.) Humans are part of the natural world, and like all living things, we use resources from the environment and produce wastes. However, the human species is unusual in its ability to use technology to extend its reach, draw- ing heavily on the natural resources of the Earth and changing environments to suit its needs. The human population has expanded to cover most of the Earth, and the numbers just keep on growing. Yet as humans draw more heavily upon the Earth’s resources, we’re putting stress on many other species and possibly driving them to extinction. The great lesson of biological evolution (a topic we cover in Chapter 12) is that not only do populations change over time but they’re also capable of going extinct. The challenge that humans face today is discovering ways to get what we need but still live in balance with the Earth’s various ecosystems. Getting Up Close and Personal with the Anatomy and Physiology of Animals All animals work hard to maintain homeostasis, or internal balance, as change occurs in the environment around them (see Chapter 13 for more on homeo- stasis). In a complex, multicellular animal like you, all of your organ systems must work together to maintain homeostasis. Following is a rundown of all of your organ systems, including what they do and what they consist of: ✓ Skeletal system: Provides support, helps with movement, and forms blood cells. Made up of your bones (see Chapter 14). ✓ Muscular system: Enables movement. Consists of your skeletal and smooth muscles (see Chapter 14). 12 Part I: Biology Basics ✓ Respiratory system: Brings in oxygen and expels carbon dioxide. Made up of your lungs and airways (see Chapter 15). ✓ Circulatory system: Transports materials throughout the body. Consists of your heart, blood, and blood vessels (see Chapter 15). ✓ Digestive system: Takes up nutrients and water and eliminates wastes. Made up of your stomach, intestines, liver, and pancreas (see Chapter 16). ✓ Excretory system: Maintains the balance of water and electrolytes in your body and removes wastes. Consists of your kidneys and bladder (see Chapter 16). ✓ Integumentary system: Serves as your first line of defense against infec- tion. Made up of your skin (see Chapter 17). ✓ Immune system: Defends against foreign invaders. Consists of your thymus, spleen, and lymph nodes (see Chapter 17). ✓ Nervous system: Controls your body functions via electrical signals. Made up of your brain, spinal cord, and nerves (see Chapter 18). ✓ Endocrine system: Produces hormones that control your body func- tions. Consists of your glands (see Chapter 18). ✓ Reproductive system: Is responsible for sexual reproduction. Made up of ovaries, fallopian tubes, a uterus, a cervix, a vagina, and a vulva if you’re female, and testes, a scrotum, vas deferens, a prostate gland, seminal vesicles, and a penis if you’re male (see Chapter 19). Comparing Plants to People At first glance, plants seem pretty different from people, but actually humans and plants occupy nearby branches on the tree of life. Both humans and plants engage in sexual reproduction, meaning they produce new offspring from the fusion of sperm and eggs that contain half the genetic material of the parents (see Chapter 20 for more information on how plants reproduce). Also like you, plants have systems for moving materials throughout their bodies (flip to Chapter 21 for the scoop on this), and they even control their functions with hormones. Of course, plants also have major differences from humans. Most impor- tantly, they make their own food using carbon dioxide, water, and energy from the Sun, whereas humans have to eat other organisms to survive. As a byproduct of their food production, plants give off oxygen as waste. Humans gladly breathe oxygen in and return the favor by breathing out carbon diox- ide that the plants can use to make food (see Chapter 5 for more on photo- synthesis and respiration and how they lead to this gas exchange between humans and plants). Chapter 2 How Life Is Studied In This Chapter ▶ Studying life ▶ Using observations to solve the world’s mysteries ▶ Recognizing science as an always-changing thing ▶ Discovering where to find scientists’ research and conclusions B iology wouldn’t have gotten very far as a science if biologists hadn’t used structured processes to conduct their research and hadn’t com- municated the results of that research with others. This chapter explores the characteristics that distinguish living things from the nonliving materials in the natural world. It also introduces you to the methods scientists (whether they’re biologists, physicists, or chemists) use to investigate the world around them and the tools they use to communicate what they’ve discovered. Living Things: Why Biologists Study Them and What Defines Them Biologists seek to understand everything they can about living things, including ✓ The structure and function of all the diverse living things on planet Earth ✓ The relationships between living things ✓ How living things grow, develop, and reproduce, including how these processes are regulated by DNA, hormones, and nerve signals ✓ The connections between living things, as well as the connections between living things and their environment ✓ How living things change over time ✓ How DNA changes, how it’s passed from one living thing to another, and how it controls the structure and function of living things 14 Part I: Biology Basics An individual living thing is called an organism. Organisms are part of the natural world — they’re made of the same chemicals studied in chemistry and geology, and they follow the same laws of the universe as those studied in physics. What makes living things different from the nonliving things in the natural world is that they’re alive. Granted, life is a little hard to define, but biologists have found a way. All organisms share eight specific characteristics that define the properties of life: ✓ Living things are made of cells that contain DNA. A cell is the smallest part of a living thing that retains all the properties of life. In other words, it’s the smallest unit that’s alive. DNA, short for deoxyribonucleic acid, is the genetic material, or instructions, for the structure and function of cells. (We fill you in on cells, including the differences between plant and animal cells, in Chapter 4, and we tell you all about the structure of DNA in Chapter 3.) ✓ Living things maintain order inside their cells and bodies. One law of the universe is that everything tends to become random over time. According to this law, if you build a sand castle, it’ll crumble back into sand over time. You never see a castle of any kind suddenly spring up and build itself or repair itself, organizing all the particles into a compli- cated castle structure. Living things, as long as they remain alive, don’t crumble into little bits. They constantly use energy to rebuild and repair themselves so that they stay intact. (To find out how living things obtain the energy they need to maintain themselves, turn to Chapter 5.) ✓ Living things regulate their systems. Living things maintain their inter- nal conditions in a way that supports life. Even when the environment around them changes, organisms attempt to maintain their internal con- ditions. Think about what happens when you go outside on a cool day without wearing a coat. Your body temperature starts to drop, and your body responds by pulling blood away from your extremities to your core in order to slow the transfer of heat to the air. It may also trigger shivering, which gets you moving and generates more body heat. These responses keep your internal body temperature in the right range for your survival even though the outside temperature is low. (When living things maintain their internal balance, that’s called homeostasis; you can find out more about homeostasis in Chapter 13.) ✓ Living things respond to signals in the environment. If you pop up sud- denly and say “Boo!” to a rock, it doesn’t do anything. Pop up and say “Boo!” to a friend or a frog, and you’ll likely see him or it jump. That’s because living things have systems to sense and respond to signals. Many animals sense their environment through their five senses just like you do, but even less familiar organisms, such as plants and bacteria, can sense and respond. (Have you ever seen a houseplant bend and grow toward sunlight? Then you’ve seen one of the responses triggered by a plant cell detecting the presence of light.) Want to know more about the systems that help plants and animals respond to signals? Flip Chapter 2: How Life Is Studied 15 to Chapter 18 to read all about the human nervous system and Chapter 21 to discover the details about plant hormones. ✓ Living things transfer energy among themselves and between them- selves and their environment. Living things need a constant supply of energy to grow and maintain order. Organisms such as plants cap- ture light energy from the Sun and use it to build food molecules that contain chemical energy. Then the plants, and other organisms that eat the plants, transfer the chemical energy from the food into cellular processes. As cellular processes occur, they transfer energy back to the environment as heat. (For more on how energy is transferred from one living thing to another, check out Chapter 11.) ✓ Living things grow and develop. You started life as a single cell. That cell divided to form new cells, which divided again. Now your body is made of approximately 100 trillion cells. As your body grew, your cells received signals that told them to change and become special types of cells: skin cells, heart cells, liver cells, brain cells, and so on. Your body developed along a plan, with a head at one end and a “tail” at the other. The DNA in your cells controlled all of these changes as your body developed. (For the scoop on the changes that occur in animal cells as they grow and develop, see Chapter 19.) ✓ Living things reproduce. People make babies, hens make chicks, and plasmodial slime molds make plasmodial slime molds. When organisms reproduce, they pass copies of their DNA onto their offspring, ensuring that the offspring have some of the traits of the parents. (Flip to Chapter 6 for full details on how cells reproduce and Chapter 19 for insight into how animals, particularly humans, make more animals.) ✓ Living things have traits that evolved over time. Birds can fly, but most of their closest relatives — the dinosaurs — couldn’t. The oldest feath- ers seen in the fossil record are found on a feathered dinosaur called Archaeopteryx. No birds or feathers have been found in any fossils that are older than those of Archaeopteryx. From observations like these, sci- entists can infer that having feathers is a trait that wasn’t always present on Earth; rather, it’s a trait that developed at a certain point in time. So, today’s birds have characteristics that developed through the evolution of their ancestors. (Ready to dig into the nitty-gritty details of evolution? See Chapter 12.) Making Sense of the World through Observations The true heart of science isn’t a bunch of facts — it’s the method that scien- tists use to gather those facts. Science is about exploring the natural world, making observations using the five senses, and attempting to make sense of 16 Part I: Biology Basics those observations. Scientists, including biologists, use two main approaches when trying to make sense of the natural world: ✓ Discovery science: When scientists seek out and observe living things, they’re engaging in discovery science, studying the natural world and looking for patterns that lead to new, tentative explanations of how things work (these explanations are called hypotheses). If a biologist doesn’t want to disturb an organism’s habitat, he or she may use obser- vation to find out how a certain animal lives in its natural environment. Making useful scientific observations involves writing detailed notes about the routine of the animal for a long period of time (usually years) to be sure that the observations are accurate. Many of the animals and plants you’re familiar with were first identified during a huge wave of discovery science that took place in the 1800s. Scientists called naturalists traveled the world drawing and describing every new living thing they could find. Discovery science continues today as biologists attempt to identify all the tiniest residents of planet Earth (bacteria and viruses) and explore the oceans to see the strange and fabulous creatures that lurk in its depths. ✓ Hypothesis-based science: When scientists test their understanding of the world through experimentation, they’re engaging in hypothesis-based science, which usually calls for following some variation of a process called the scientific method (see the next section for more on this). Modern biologists are using hypothesis-based science to try and under- stand many things, including the causes and potential cures of human diseases and how DNA controls the structure and function of living things. Hypothesis-based science can be a bit more complex than discovery science, which is why we spend the next two sections introducing you to two impor- tant elements of hypothesis-based science: scientific method and experiment design. Introducing the scientific method The scientific method is basically a plan that scientists follow while perform- ing scientific experiments and writing up the results. It allows experiments to be duplicated and results to be communicated uniformly. Here’s the general process of the scientific method: 1. First, make observations and come up with questions. The scientific method starts when scientists notice something and ask questions like “What’s that?” or “How does it work?” just like a child might when he sees something new. Chapter 2: How Life Is Studied 17 2. Then form a hypothesis. Much like Sherlock Holmes, scientists piece together clues to try and come up with the most likely hypothesis (explanation) for a set of observations. This hypothesis represents scientists’ thinking about pos- sible answers to their questions. Say, for example, a marine biologist is exploring some rocks along a beach and finds a new worm-shaped creature he has never seen before. His hypothesis is therefore that the creature is some kind of worm. One important point about a scientific hypothesis is that it must be test- able, or falsifiable. In other words, it has to be an idea that you can sup- port or reject by exploring the situation further using your five senses. 3. Next, make predictions and design experiments to test the idea(s). Predictions set up the framework for an experiment to test a hypothesis, and they’re typically written as “if... then” statements. In the preceding worm example, the marine biologist predicts that if the creature is a worm, then its internal structures should look like those in other worms he has studied. 4. Test the idea(s) through experimentation. Scientists must design their experiments carefully in order to test just one idea at a time (we explain how to set up a good experiment in the later “Designing experiments” section). As they conduct their experiments, sci- entists make observations using their five senses and record these obser- vations as their results or data. Continuing with the worm example, the marine biologist tests his hypothesis by dissecting the wormlike creature, examining its internal parts carefully with the assistance of a microscope, and making detailed drawings of its internal structures. Discovery science of the 20th century Although discovery science about the types the very tiny, but very complex, landscape of of plants and animals on Earth had its heyday the 46 human chromosomes that contain the in the 1800s, discovery science about life on collection of all the genes found in humans. a level that’s too small to see with the naked Each of the 25,000 genes they located provides eye is ongoing. One incredibly important proj- information about inherited traits. The traits ect that employed modern discovery science is range from little things, such as whether you the Human Genome Project, which set out to can curl your tongue or not, to truly important map where each trait is found on the 46 human things, such as whether you have a genetic risk chromosomes. for developing breast cancer or cystic fibrosis. By finding out where genes are located, scien- Instead of traveling across the oceans to tists can turn their attention to using this new- explore the world and catalog living things like found information to develop hypotheses about the discovery scientists of 200 years ago, sci- cures and gene therapies. entists from all over the world set out to explore 18 Part I: Biology Basics 5. Then make conclusions about the findings. Scientists interpret the results of their experiments through deductive reasoning, using their specific observations to test their general hypoth- esis. When making deductive conclusions, scientists consider their origi- nal hypothesis and ask whether it could still be true in light of the new information gathered during the experiment. If so, the hypothesis can remain as a possible explanation for how things work. If not, scientists reject the hypothesis and try to come up with an alternate explanation (a new hypothesis) that could explain what they’ve seen. In the earlier worm example, the marine biologist discovers that the internal struc- tures of the wormlike creature look very similar to another type of worm he’s familiar with. He can therefore conclude that the new animal is likely a relative of that other type of worm. 6. Finally, communicate the conclusions with other scientists. Communication is a huge part of science. Without it, discoveries can’t be passed on, and old conclusions can’t be tested with new experiments. When scientists complete some work, they write a paper that explains exactly what they did, what they saw, and what they concluded. Then they submit that paper to a scientific journal in their field. Scientists also present their work to other scientists at meetings, including those sponsored by scientific societies. In addition to sponsoring meetings, these societies support their respective disciplines by printing scientific journals and providing assistance to teachers and students in the field. Designing experiments Any scientific experiment must have the ability to be duplicated because the “answer” the scientist comes up with (whether it supports or refutes the origi- nal hypothesis) can’t become part of the scientific knowledge base unless other scientists can perform the exact same experiment and achieve the same results. When a scientist designs an experiment, he tries to develop a plan that clearly shows the effect or importance of each factor tested by his experi- ment. Any factor that can be changed in an experiment is called a variable. Three kinds of variables are especially important to consider when designing experiments: ✓ Experimental variables: The factor you want to test is an experimental variable (also called an independent variable). ✓ Responding variables: The factor you measure is the responding vari- able (also called a dependent variable). ✓ Controlled variables: Any factors that you want to remain the same between the treatments in your experiment are controlled variables. Chapter 2: How Life Is Studied 19 Scientific experiments help people answer questions about the natural world. To design an experiment: 1. Make observations about something you’re interested in and use inductive reasoning to come up with a hypothesis that seems like a good explanation or answer to your question. Inductive reasoning uses specific observations to generate general principles. 2. Think about how to test your hypothesis, creating a prediction about it using an “if... then” statement. 3. Decide on your experimental treatment, what you’ll measure, and how often you’ll make measurements. The condition you alter in your experiment is your experimental vari- able. The changes you measure are your responding variables. 4. Create two groups for your experiment: an experimental group and a control group. The experimental group receives the experimental treatment; in other words, you vary one condition that might affect this group. The control group should be as similar as possible to your experimental group, but it shouldn’t receive the experimental treatment. 5. Set up your experiment, being careful to control all the variables except the experimental variable. 6. Make your planned measurements and record the quantitative and qualitative data in a notebook. Quantitative data is numerical data, such as height, weight, and number of individuals who showed a change. It can be analyzed with statistics and presented in graphs. Qualitative data is descriptive data, such as color, health, and happiness. It’s usually presented in paragraphs or tables. Be sure to date all of your observations. 7. Analyze your data by comparing the differences between your experi- mental and control groups. You can calculate the averages for numerical data and create graphs that illustrate the differences, if any, between your two groups. 8. Use deductive reasoning to decide whether your experiment supports or rejects your hypothesis and to compare your results with those of other scientists. 9. Report your results, being sure to explain your original ideas and how you conducted your experiment, and describe your conclusions. As an example of how you design an experiment, imagine you’re a marathon runner who trains with a group of friends. You wonder whether you and your 20 Part I: Biology Basics friends will be able to run marathons faster when you eat pasta the night before the race. To answer your question, follow the scientific method and design an experiment. 1. Form your hypothesis. Your hunch is that loading up on pasta will give you the energy you need to run faster the next day. Translate that hunch into a proper hypothesis, which looks something like this: The time it takes to run a marathon is improved by consuming large quantities of carbohydrates prerace. 2. Treat one group with your experimental variable. In order to test your hypothesis, convince half of your friends to eat lots of pasta the night before the race. Because the factor you want to test is the effect of eating pasta, pasta consumption is your experimental variable. 3. Create a control group that doesn’t receive the experimental variable. You need a comparison group for your experiment, so you convince half of your friends to eat a normal, nonpasta meal the night before the race. For the best results in your experiment, this control group should be as similar as possible to your experimental group so you can be pretty sure that any effect you see is due to the pasta and not some other factor. So, ideally, both groups of your friends are about the same age, same gender, and same fitness level. They’re also eating about the same thing before the race — with the sole exception being the pasta. All the factors that could be different between your two groups (age, gender, fitness, and diet) but that you try to control to keep them the same are your controlled variables. 4. Measure your responding variable. Race time is your responding variable because you determine the effect of eating pasta by timing how long it takes each person in your group to run the race. Because scientists carefully record exact measure- ments from their experiments and present that data in graphs, tables, or charts, you average the race times for your friends in each of the two groups and present the information in a small table. 5. Compare results from your two groups and make your conclusions. If your pasta-eating friends ran the marathon an average of two minutes faster than your friends who didn’t eat pasta, you may conclude that your hypothesis is supported and that eating pasta does in fact help marathon runners run faster races. Chapter 2: How Life Is Studied 21 One man’s error is another man’s starting point In the early 1900s, a Russian researcher named three different groups. The first group was fed A.I. Ignatowski fed rabbits a diet of milk and a supplement of muscle fluid, the second group eggs. He found that the rabbits’ aortas devel- was fed only egg whites, and the third group oped the same kind of plaques that form in was fed only egg yolks. Only the yolk-eating people with atherosclerosis. Ignatowski wasn’t rabbits developed plaques in their aortas. The ignorant, but he assumed that the atherosclero- young researchers ran the experiment again; sis was caused by the proteins in the milk and this time they analyzed the atherosclerotic eggs. He was wrong. plaques to look for any concentrated chemi- cal substances. In 1913, Anichkov and his col- A younger researcher who was working in leagues discovered that cholesterol in the egg the same pathology department at the time, yolk was responsible for creating plaques in the a Russian named Nikolai Anichkov, knew of aorta. Their discovery may not have been possi- Ignatowski’s work. Anichkov and some of his ble if Ignatowski had never conducted his exper- colleagues repeated Ignatowski’s study with iment (or if he’d beaten them to the punch!). one small change: They split the rabbits into Before you can consider your research complete, you need to look at a few more factors: ✓ Sample size: The number of individuals who receive each treatment in an experiment is your sample size. To make any kind of scientific research valid, the sample size has to be rather large. If you had only four friends participate in your experiment, you’d have to conduct your experiment again on much larger groups of runners before you could proudly proclaim that consuming large quantities of carbohydrates pre- race helps marathon runners improve their speed. ✓ Replicates: The number of times you repeat the entire experiment, or

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