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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
- Veröffentlichungsjahr: 2012
From genetics to ecology -- the easy way to score higher in biology Are you a student baffled by biology? You're not alone. With the help of Biology Workbook For Dummies you'll quickly and painlessly get a grip on complex biology concepts and unlock the mysteries of this fascinating and ever-evolving field of study. Whether used as a complement to Biology For Dummies or on its own, Biology Workbook For Dummies aids you in grasping the fundamental aspects of Biology. In plain English, it helps you understand the concepts you'll come across in your biology class, such as physiology, ecology, evolution, genetics, cell biology, and more. Throughout the book, you get plenty of practice exercises to reinforce learning and help you on your goal of scoring higher in biology. * Grasp the fundamental concepts of biology * Step-by-step answer sets clearly identify where you went wrong (or right) with a problem * Hundreds of study questions and exercises give you the skills and confidence to ace your biology course If you're intimidated by biology, utilize the friendly, hands-on information and activities in Biology Workbook For Dummies to build your skills in and out of the science lab.
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Biology Workbook For Dummies®
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Table of Contents
Biology Workbook For Dummies®
by René Fester Kratz, PhD
Biology Workbook For Dummies®
Published by John Wiley & Sons, Inc. 111 River St. Hoboken, NJ 07030-5774 www.wiley.com
Copyright © 2012 by John Wiley & Sons, Inc., Hoboken, New Jersey
Published by John Wiley & Sons, Inc., Hoboken, New Jersey
Published simultaneously in Canada
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Library of Congress Control Number: 2012935793
ISBN 978-1-118-15840-1 (pbk); ISBN 978-1-118-22606-3 (ebk); ISBN 978-1-118-26404-1 (ebk); ISBN 978-1-118-23936-0 (ebk)
Manufactured in the United States of America
10 9 8 7 6 5 4 3 2 1
About the Author
René Fester Kratz, PhD, grew up near the ocean in Rhode Island. From a young age, she wanted to be a teacher (because she loved her teachers at school) and a biologist (because her dad was one). She graduated from Warwick Veterans Memorial High School and went on to major in biology at Boston University. As a freshman and sophomore at BU, René got excited by subjects other than biology and even considered changing her major. Then, she met and studied under Lynn Margulis, who reignited René’s love of biology and introduced her to the world of microbes. René graduated with a BA in biology from BU and went on to earn an MS and a PhD in botany from the University of Washington. At UW, René studied reproductive onset in Acetabularia acetabulum, a marine green alga that grows as single cells big enough to pick up with your fingers. When they enter reproduction, the cells of A. acetabulum form a flat disk or cup-shaped structure at the top, earning the alga the nickname of the “mermaid’s wine glass.”
René currently teaches biology and general science classes at Everett Community College in Everett, Washington. She spends most of her time introducing students to the wonders of cells and microbes as she teaches cellular biology and microbiology. René also has a strong interest in science education and science literacy for everyone. As a member of the North Cascades and Olympic Science Partnership, she helped create inquiry-based science courses for future teachers that are based on research on human learning. She loves teaching these courses because they make science accessible for all kinds of people. In the summer, René enjoys working with K–12 teachers on the improvement of science education in the public schools. She also enjoys writing about science and is the author of Molecular & Cell Biology For Dummies, Biology For Dummies 2nd edition, Botany For Dummies (all published by Wiley), and E–Z Microbiology, 2nd edition (Barron’s Educational Press).
René loves living in the Pacific Northwest because she is near the ocean and her daffodils start blooming in February (when her family back East is still shoveling snow). She doesn’t mind the rain and thinks the San Juan Islands are one of the most beautiful places on Earth. Her husband, two sons, and two very bad dogs help her remember what is truly important, and her “sisters” help keep her sane. René loves to scrapbook, stitch, garden, and read.
Dedication
Happy 70th birthday to my mom, Annette — without your support and encouragement, I wouldn’t be where I am today. Love you always.
Author’s Acknowledgments
Thanks to Matt Wagner of Fresh Books, Inc., for helping me find the opportunity to work on this book. And thanks to all the great people at Wiley who made it happen: my project editor, Heike Baird; the executive editor, Lindsay Lefevere, who helped get me started on the project; Alicia South, who coordinated the art; and Kimberly Lyle-Ippolito and Allison Thomas, my technical reviewers. Thanks also to Nikki Gee, the project coordinator.
On the home front, thanks to my husband, Dan, and my sons, Hueston and Dashiel, for all their love and support.
Publisher’s Acknowledgments
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Introduction
Living things are all around you, from the bacteria that live on your skin to the green plants that cover the land to the majestic blue whales that swim through the ocean. You’re aware of many of these forms of life, but have you ever taken a look at the single-celled creatures in a drop of pond water? Or thought about the many different ways your life depends on the actions of plants and bacteria? The journey to discover more about the living world around you is at the heart of biology.
A living organism can be as simple as a single cell or as complex as a human being, but no matter how different they may seem, all living things on Earth have fundamental similarities: They’re made of cells that contain DNA, and they all grow, move, get energy, use raw materials, make waste, and reproduce. These similarities among all living things illustrate how all life on Earth is part of the same big family tree. And the differences in how each type of living thing achieves these same goals — well, the differences are what make biology fascinating.
Beyond increasing your appreciation for other kinds of life, the science of biology can help you understand your place in the living world. At first glance, you may think that people can do everything for themselves — get food from the grocery store, build their homes, and make their clothes — but a closer look quickly shows how dependent people are on the rest of the living world. People depend on plants and green bacteria to make the food that supports food chains that include agricultural species. These green organisms also make the oxygen that people need to sustain life. Bacteria and fungi in the soil break down dead organisms, recycling matter so that other living things can reuse it. Clearly, people can’t survive on planet Earth alone.
I hope that you enjoy your exploration of the living world and come to appreciate the marvelous diversity of life on Earth. I also hope that the information in this book improves your performance in biology class, specifically (gulp!) your exams. This truly is a living planet, and the more that people understand the connections among living things, the better choices they’ll make about the future of the world.
About This Book
Biology Workbook For Dummies is designed to help supplement your learning in a biology class or to use as a companion for your self-guided exploration of biology using Biology For Dummies, 2nd edition (Wiley). This workbook isn’t intended to replace a textbook but rather to highlight essential information in an easy-to-understand format and quiz you on it. I provide many straightforward lists of the fundamentals you need to know about the various subjects you’d typically encounter in a biology class, along with problems on which you can practice and reinforce your understanding. I provide answers to all the practice questions and include explanations of why some answers are right or wrong.
If you’re taking biology, your instructor may present material in a different order than the organization I use here, so be sure to take advantage of both the table of contents and the index to navigate where you need to go.
Conventions Used in This Book
In order to explain topics as clearly as possible, I keep scientific jargon to a minimum and present information in a straightforward, linear style. I break dense information into main concepts and divide complicated processes into series of steps.
To help you find your way through the subjects in this book, I use the following style conventions:
I use italic for emphasis and to highlight new words or terms that I define in the text.
I use boldface to indicate key words in bulleted lists and the action parts of numbered steps.
I use monofont for web addresses so they’re easy to recognize.
When this book was printed, some web addresses may have needed to break across two lines of text. If that happened, know that I haven’t put in any extra characters (such as hyphens) to indicate the break. So when using one of these web addresses, type in exactly what you see and ignore the line break.
Foolish Assumptions
As I wrote this book, I tried to imagine who you might be and what you might need to understand biology, and here are some assumptions I made:
You may be a high school student taking biology and maybe preparing for an advanced placement test or a college entrance examination. For you, I’ve tried to extract the essentials about each subject and organize them into short lists that are easier to study than long paragraphs. I’ve also written problems for you to practice on and given you links to websites with great animations and tutorials.
You may be a college student who isn’t a science major but is taking a biology class to help fulfill your degree requirements. For you, I’ve tried to get the main ideas across with as little scientific jargon as possible. If you find that you get overwhelmed in your biology class, try reading a section in this workbook before you go to class to hear a lecture about the topic. That way, you’ll have some of the big ideas in your mind before your instructor starts adding all the details. Also, many non-science students are a little shocked to find that their usual study habits don’t work well for a science class, so be sure to read my tips in Chapter 20 on how to get an A in biology.
You may be someone who just wants to know a little bit more about the living world around you. You may have picked up Biology For Dummies, 2nd edition, or some other biology text because you want to take a deeper look at the living world. For you, this workbook will make a nice companion and give you a chance to test yourself on the practice problems to see how well you’re learning the information.
Whatever your reason for picking up this book, I’ve done my best to explain the topics of biology simply and effectively and to create some challenging practice problems to help improve your learning. I hope you find this workbook helpful.
How This Book Is Organized
I’ve arranged this book to follow the order of topics in many biology textbooks, with a few minor differences. Like all For Dummies books, each chapter is self-contained, so you can pick up the book whenever you need it and jump into the topic you’re working on. After I explain a subject, I use that information in later topics. So 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, I refer you to the appropriate section or chapter.
Part I: Getting the Basics
Biology is the study of life, but as I’m sure you know, life is complex. To simplify it, I break the all-encompassing subject of biology into smaller, more palatable chunks. To start, I explain the way that scientists study biology. This scientific method holds not only for biology but also for chemistry, psychology, physics, geology, and other sciences and social sciences. Knowing how scientists conduct, challenge, check, and recheck research makes it easier to appreciate the value of scientific information.
In this part, I spotlight the 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 have millions. After you have a grasp of how cells are the powerhouses of bodies, I review the types of molecules that are important to their functioning. Included in this first part is the often-dreaded but oh-so-necessary review of basic chemistry. To learn biology, you must understand some basic principles of how chemicals function. After all, the bodies of every living organism are big sacs of chemicals. Chemical reactions generate every process that occurs in your body, such as those that occur during the metabolic processes in plant and animal cells. So in this part you delve into topics such as enzymes, energy transfer, and how plants make food from scratch, using just carbon dioxide and water!
Part II: Creating the Future with Cell Division and Genetics
Cells reproduce, giving rise to other cells. Sometimes cells make exact copies of themselves in order to repair, grow, or produce offspring that are genetically identical to the parent. Some organisms mix it up a little by engaging in sexual reproduction, creating offspring that have combinations of genes that are different from those of their parents.
But whether organisms reproduce asexually or sexually, the parents’ traits are visible in their offspring. Ducks make ducklings, and from little acorns mighty oaks do grow. Offspring inherit their traits from their parents because parents pass DNA to their offspring. DNA contains the blueprints for proteins that do the work in cells and thus determine an organism’s characteristics. Biologists today are busy unraveling the mysteries of DNA, giving humans unprecedented power over the very stuff of life. This part walks you through all these topics and gives you plenty of chances to test yourself on what you’ve read.
Part III: Making Connections with Ecology and Evolution
All the amazingly diverse forms of life on Earth interact with one another. In this part, you become more aware of the living part of Earth as one big, interconnected ecosystem called the biosphere. Living things aren’t just connected with one another today; they also have connections to the living things of the past. The science of evolution studies those relationships and uses them to understand present and future changes in the populations of living things on Earth today.
Part IV: Getting to Know the Human Body
Organisms respond to changes in their environment, trying to maintain their internal conditions within a range that supports life. Animals have many different systems that support this balance, which is called homeostasis. In this part, I explain most of the systems that support the structure and function of the human body and touch on how humans compare to other animals.
Part V: Going Green with Plant Biology
Our green neighbors are very quiet and sometimes get overlooked in the hustle and bustle of animal life. However, the importance of plants to life on Earth simply can’t be overstated — they’re the food makers, after all. Without plants (and green microbes), nobody else would have anything to eat! And when you take a good look (and you do in this part), plants are pretty interesting. Just like animals, they’re made of cells and have systems to transport materials around their body and exchange matter and energy with their environment. Their structures are well suited to their lifestyle, and many plants are things of beauty. Just ask someone in your life who likes to garden! To test your green thumb, flip to the chapters in this part.
Part VI: The Part of Tens
This part contains two short chapters with lists of ten or so items. I give you tips for getting an A in biology and links for some websites that will help you do just that!
Icons Used in This Book
I use the familiar For Dummies icons here to help guide you and give you new insights as you read the material.
The text near this bull’s-eye symbol may help you remember the facts being discussed or suggest a way to help you commit them to memory. Also, although you can learn most biological information on its own, some topics aren’t clear unless the building blocks of information are stacked. In those instances, I provide info at this icon that I may have explained in an earlier chapter.
This icon marks sample problems that I’ve laid out step by step to help guide you through the solution. Reviewing these problems will help you answer similar problems in the practice problems or in those assigned by your biology instructor.
This icon serves to summon your memory. The information I spotlight here is info I think you should permanently store in your brain’s biology file. If you want a quick review of biology, scan the book reading the text by these icons. No need for a chunky yellow highlighter.
The bomb icon marks ideas that commonly trip up students of biology. To move beyond these common misunderstandings, you need to confront them head on, and this icon helps you do that.
Where to Go from Here
With Biology Workbook For Dummies, you can start anywhere in the book that you want. If you’re in the thick of a biology class and having trouble, jump right to the subject that’s confusing you. If you’re using the book as a companion to a biology class that’s just beginning, the book follows the organization of most college classes, with one exception — most college classes work from the smallest to the largest, starting with molecules and then moving on to cells. I prefer to start with cells to give you a sense of context and then move on to the molecules. If you’re reading this workbook for general interest, you’ll probably find it best to begin at the beginning with the chapter on cells and then move on to whatever interests you next. Whatever your circumstance, the table of contents and index help you find the information you need.
I wrote this book with the non-scientist in mind. If you’re taking your study of biology further and need more information, several other For Dummies books expand on the topics that I present in general terms here:
My book Molecular and Cellular Biology For Dummies (Wiley) takes a deeper look into cells, basic cellular chemistry, metabolism, genetics, and the study of DNA.
Anatomy & Physiology For Dummies, by Maggie Norris and Donna Rae Siegfried, presents more details on the structure and function of the human body, and Anatomy & Physiology Workbook For Dummies, by Janet Rae-Dupree and Pat DuPree, gives you lots of practice problems on the subject. Both of these books are published by Wiley.
Evolution For Dummies, by Greg Krukonis and Tracy Barr (Wiley), explores the topic of evolution more fully, looking at the evidence for evolution and the many mechanisms by which it occurs.
Best wishes from me to you as you begin your exploration of life on Earth.
Part I
Getting the Basics
In this part . . .
Biology is the scientific study of living things. Like all scientists, biologists use their five senses to ask questions about the natural world. Biologists follow a scientific method of asking questions, proposing answers, and then testing those answers through experimentation. This book starts off by explaining more about the scientific method and giving you some opportunities to practice using it.
All living things are made of cells, and cells are made of molecules. Living things with many cells, like humans, are organized into organ systems, organs, tissues, and cells. Cells are the smallest things that show all the properties of life, so this part gets you acquainted with cells so you can understand more about everything around you. I describe the structure of cells and the molecules that make them up, and then I explain how cells get the energy they need to function.
Chapter 1
Figuring Out the Scientific Method
In This Chapter
Testing hypotheses using the scientific method
Conducting scientific experiments the right way
Distinguishing between hypotheses and theories
Biology is the branch of science that deals with living things. Biology wouldn’t have gotten very far as a science if biologists hadn’t used structured processes to conduct their research and hadn’t communicated the results of that research with others. You can use what you learn in this chapter in your everyday life to take a closer look at the information that swirls all around you. Does that diet plan really work? What studies did they do? Ninety-seven percent of scientists agree that global warming is really happening. Why do they think that? What evidence are they looking at? This chapter introduces you to the methods that scientists (whether they’re biologists, physicists, or chemists) use to investigate the world around them and helps you learn to analyze scientific experiments.
Developing Hypotheses
The true heart of science isn’t a bunch of facts; it’s the method that scientists use to gather those facts. Science is about exploring the natural world, making observations using the five senses and intellect, and attempting to make sense of those observations.
When scientists seek out, observe, and describe living things, they’re engaging in discovery science. Scientists practice discovery science as they explore new environments, like the deep sea, describing the organisms they find there. As scientists study the natural world, they look for patterns and attempt to make sense of how things work. When a scientist proposes an untested explanation for how things work, the tentative explanation is called a hypothesis. 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 section “Practicing the Scientific Method” later in the chapter). For a hypothesis to be accepted by scientists, it must be testable or falsifiable. In other words, it must be an idea that you can support or reject by exploring the situation further and collecting observations using your five senses.
For example, let’s say that you have a bird feeder in your backyard. You keep filling the feeder with birdseed, but every day when you get up, it’s empty again. When you examine the feeder, you notice some scratches near the feeder hole that look like marks from animal claws, so you think that squirrels may be getting into your birdseed. So you take some wire screen and nail it over the feeder hole to reduce the size of the openings. After that, your birdseed lasts for days, and you observe birds eating at your bird feeder.
In my example, you took a scientific approach to solving your bird feeder problem.
You made initial observations about your bird feeder constantly being emptied and further observed the scratch marks around the feeder hole.
You came up with a hypothesis about the cause of the disappearing food: If a squirrel is stealing the food, then a smaller opening on the bird feeder would prevent that.
You were able to test your hypothesis by making a change (creating a smaller opening) and then making new observations.
If an explanation isn’t testable, it’s not considered a scientific hypothesis.
In the bird feeder example, you may have thought, “Squirrels really enjoy annoying birds, and that’s why they’re stealing the food.” This explanation relates to your observations, but unless you’re an expert in reading squirrel emotions, it’s not really something you can test and it wouldn’t be considered a scientific hypothesis.
See if you can think like a scientist by answering these questions about observations and hypotheses:
1. Two scientists are mapping the locations of mushrooms in the Amazon rain forest. Thus, they’re practicing
a. Discovery science
b. Hypothesis-based science
c. Making observations
d. Discovery science and making observations
2. One night as it gets dark, the scientists notice that some mushrooms glow in the dark. Which of the following would be a valid scientific hypothesis about this observation?
a. The mushrooms glow because they’re scared of the dark.
b. The mushrooms glow to attract certain insects.
c. The glowing mushrooms appear yellow-green in color.
Practicing the Scientific Method
Although the bird feeder and squirrel story from the preceding section is an everyday example, it illustrates the most important components of the scientific method. Scientists use the same procedure to make sense of the world whether they’re studying squirrels in the backyard or the potential for life outside planet Earth, and that procedure is the scientific method.
The scientific method is basically a six-step plan that scientists follow while performing scientific experiments and writing up the results. By following the scientific method carefully, scientists make sure that their conclusions are based on observations and that other scientists can repeat their experiments. Here’s the general process of the scientific method:
1. First, make observations and come up with questions.
The scientific method starts by scientists noticing something and asking questions like “What’s that?” or “How does it work?” — just like a child might when he sees something new, such as an earthworm wriggling in a puddle after a rainstorm.
2. Then form a hypothesis.
Scientists form hypotheses using inductive reasoning; that is, they use specific observations to try and come up with general principles. Say, for example, a marine biologist is exploring a beach and finds a new worm-shaped creature he has never seen before. Using inductive reasoning, he may reach the hypothesis that the creature is some kind of worm because it’s shaped like a worm.
3. Next, make predictions and design experiments to test those ideas.
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 ideas through experimentation.
Scientists must design their experiments carefully to test just one idea at a time (I explain how to set up a good experiment in the “Designing Experiments” section, later in the chapter). As they conduct their experiments, scientists make observations using their five senses and record these observations 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 structure.
Any scientific experiment must have the ability to be duplicated because the “answer” the scientist comes up with (whether it supports or rejects the original hypothesis) can’t become part of the scientific knowledge base unless other scientists can perform the exact same experiment and achieve the same results.
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 hypothesis. When making deductive conclusions, scientists consider their original hypotheses and ask whether they could still be true in light of the new information gathered during the experiment. If so, the hypotheses can remain as possible explanations for how things work. If not, scientists reject the hypotheses and try to come up with alternate explanations (new hypotheses) that can explain what they’ve seen. In the earlier worm example, the marine biologist discovers that the internal structures 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 wouldn’t be passed on, and old conclusions wouldn’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.
Continue testing your scientific thinking by answering these practice questions about the scientific method. Questions 3 through 5 refer to the following story:
Two scientists who are studying mushrooms in the Amazon rain forest discover a type of mushroom that glows in the dark. One of the scientists proposes that the mushrooms glow in order to attract a certain insect that will scatter the mushroom’s reproductive spores. The scientists watch the mushrooms for several days, collecting samples of any insects that visit the mushrooms. Then, they take some of the mushrooms and insects back to their lab and test each type of insect to see whether it’s attracted to the glowing mushroom. However, none of the insects shows any attraction to the glow. The scientists decide that the glow from the mushroom must have some other purpose than to attract any of the insects they collected.
3. Put yourself in the place of these scientists and write what you think they may have predicted for their experiment.
4. When the scientists decide that the glow from the mushroom has some other purpose than attracting any of the insects they collected, they’re
a. Making an observation
b. Collecting data
c. Using inductive reasoning
d. Using deductive reasoning
5. Which of the following is an example of the type of data the scientists may have collected during their experiment?
a. The number of times a particular type of insect flew toward the glowing mushroom.
b. A comparison of the number of times an insect flew toward the glowing mushroom and away from the glowing mushroom.
c. The purpose of the glow may be to keep insects away from the mushroom.
d. The scientists ask their colleagues who work on glowing bacteria for information about what makes bacteria glow.
Designing Experiments
When a scientist designs an experiment to test her hypothesis, she tries to develop a plan that clearly shows the effect or importance of each factor tested by her experiment. 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: Also called independent variables, these are the factors you want to test or that are controlled by the researcher.
Responding variables: Also called dependent variables, these are the factors you measure. The dependent variable depends on the independent variable and is usually what ends up in your data table.
Controlled variables: These are any factors that you want to remain the same regardless of the changes in the experimental variables.
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.
For example, you’re a runner who trains with a group of friends, and you have a hunch that loading up on pasta, which has lots of carbohydrates, gives you the energy you need to run faster the next day.
2. Think about how to test your hypothesis.
One way to help focus your thinking is to create a prediction about your hypothesis using an “if . . . then” format. Translate that hunch into a proper hypothesis, which looks something like this: If a runner consumes large quantities of carbohydrates before a race, he’ll run faster.
3. Decide on your experimental treatment.
The condition or situation you alter in your experiment is your experimental (independent) variable.You can test your hypothesis by convincing 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.
4. Decide what to measure and how often to make measurements.
The changes you measure are your responding (dependent) variables.Race duration is your responding variable because you determine the effect of eating pasta by timing how long each person in your group takes to run the race.
5. Create two groups of individuals for your experiment.
One group is your experimental group and the other is a control group.
a. The experimental group receives the experimental treatment; in other words, you vary the one condition you want to test. In this case, you feed your friends pasta.
b. The control group should be as similar as possible to your experimental group except that it doesn’t receive the experimental treatment — so, no pasta for this group.
For example, you convince half of your friends to eat a meal without pasta 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 also eat about the same thing before the race, with the sole exception of the amount of pasta they eat at dinner. 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.
Don’t confuse controlled variables with the control groups. Controlled variables are the conditions you keep the same for all your groups, while the control group is the group of subjects in your experiment that you don’t add any experimental variables to.
6. Conduct your experiment.
Your friends eat their assigned meals the night before the race and then compete in the race the next day.
7. Make your planned measurements and record them in a notebook.
Be sure to date all your observations. The observations you make are the data or results of your experiment.
a. Quantitative data is numerical data like height, weight, and number of individuals that show a change. You can analyze quantitative data with statistics and present it in graphs.
Scientists carefully record exact measurements from their experiments and present that data in graphs, tables, or charts. For this example, you average the race times for your friends in each of the two groups and present the information in a small table.
b. Qualitative data is descriptive data like color, health, and happiness. You usually present qualitative data in paragraphs or tables.
For your race experiment, you might ask your friends how they felt during the race: Did they have lots of energy? Did their energy level feel constant, or did they tire quickly?
8. Analyze your data by comparing the differences between your experimental and control groups.
You can calculate the averages for numerical data and create graphs that illustrate the differences, if any, between your two groups.
Your graph shows that your pasta-eating friends ran the marathon an average of two minutes faster than your friends who didn’t eat pasta.
9. Use deductive reasoning to decide whether your experiment supports or rejects your hypothesis and to compare your results with those of other scientists.
Because your pasta-eating friends ran faster, you may conclude that your hypothesis is supported and that eating pasta does in fact help marathon runners run faster races. You might also look at studies on other factors, like drinking enough water, and how they affect marathon speeds in order to compare the effect of your study to those of other scientists. If the best any other study did was decrease marathon times by 30 seconds and you decreased them by 2 whole minutes, you might conclude that your experimental variable — eating pasta — was more important than the variables tested in the other studies.
10. Report your results.
Explain your original ideas and how you conducted your experiment, present your results, and explain your conclusions.
For a small study like the one I’ve used as an example, you might just report it informally by telling your friends or writing about it on your blog. But if you were an exercise researcher who conducted a large, well-designed study with lots of marathon runners, you’d write an article about your work and how it compared to the work of other researchers. Scientists in every field have their own special magazines, called scientific journals. You’d find a journal appropriate to your work, like The International Journal of Exercise Science, and submit your article to the editor. The editor would send your article out to other scientists or your peers in the field so that they could examine your work and decide whether it was good work that was worthy of publishing. Peer review is incredibly important to the process of science because it gives strength to scientific conclusions when others scientists can evaluate the same data and reach the same conclusion.
Scientific articles go through a process called peer review before they’re published in scientific journals. During peer review, experts in the same field as the article’s author examine the scientist’s work to decide whether the experiments were conducted properly and whether the author’s conclusions are valid based on the evidence collected.
Analyzing an experiment and really understanding experimental design is tough stuff. To help you understand, revisit the mushroom scientists again and take a closer look at their experiments. Questions 6 through 10 refer to the following story:
Two scientists want to test whether a glow-in-the-dark mushroom glows in order to attract insects. To test their idea, they set up an experiment. First, they build three identical chambers that are completely dark. In one chamber, they put a glowing mushroom. In another chamber, they put a light that glows the exact same color as the mushroom. In the third chamber, they put a mushroom that’s a close relative to the glowing mushroom but that doesn’t glow. The scientists put the same species of insect into each chamber and observe whether the insect flies toward or away from the mushrooms or the light. They repeat this procedure several times in each chamber, using new insects of the same species each time.
6. What’s the experimental variable in the scientists’ experiment?
a. The type of insect used
b. The size of the chamber
c. The object placed in the chamber with the insect
d. The direction that the insect flies when placed in the chamber
7. What’s an example of a controlled variable in the scientists’ experiment?
a. The type of insect used
b. The light bulb placed in the chamber with the insect
c. The type of mushroom placed in the chamber with the insect
d. The direction that the insect flies when placed in the chamber
8. What’s the control group in the scientists’ experiment?
a. The type of insect used
b. The insects placed in the chamber with the glowing mushroom
c. The insects placed in the chamber with the nonglowing mushroom
d. The insects placed in the chamber with the glowing light bulb
9. Which of the following is an example of qualitative data that the scientists may have collected during their experiment?
a. The number of times the insects flew toward the test object
b. The number of times the insects flew away from the test object
c. The pattern of the insects’ flight (straight lines versus wandering)
d. The speed at which the insects flew
10. What’s the responding variable in the scientists’ experiment?
a. The type of insect used
b. The light bulb placed in the chamber with the insect
c. The type of mushroom placed in the chamber with the insect
d. The direction that the insect flies when placed in the chamber
Making an Experiment Count
A scientist may consider all the variables carefully and design a good experiment, but in order for an experiment to be valid and significant to the scientific community, it must meet these standards:
Sample size: The number of individuals that receive each treatment in an experiment is your sample size. To make any kind of scientific research valid, the sample size has to be large. If only four of your friends participate in the pasta experiment in the preceding “Designing Experiments” section, you’d have to conduct your experiment again on much larger groups of runners with hundreds of people per group before you could proudly proclaim that consuming large quantities of carbohydrates before a race helps marathon runners improve their speed. The larger the sample size, the more valid the conclusions from an experiment.
Replicates: The number of times you repeat the entire experiment or the number of groups you have in each treatment category are your replicates. Suppose you have 60 marathon-running friends and you break them into six groups of 10 runners each. Three groups eat pasta and three groups don’t, so you have three replicates of each treatment. (Your total sample size is therefore 30 for each treatment.)
Statistical significance: The mathematical measure of an experiment’s validity is referred to as statistical significance.
