Biology For Dummies
Part I Biology Basics
How Life Is Studied
In This Chapter
Using observations to solve the world’s mysteries
Recognizing science as an always-changing thing
Discovering where to find scientists’ research and conclusions
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. 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
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 complicated 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 internal conditions in a way that supports life. Even when the environment around them changes, organisms attempt to maintain their internal conditions. 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 suddenly 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 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 themselves and their environment. Living things need a constant supply of energy to grow and maintain order. Organisms such as plants capture 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 feathers 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, scientists 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 scientists use to gather those facts. Science is about exploring the natural world, making observations using the five senses, and attempting to make sense of 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 observation 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 understand 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 important 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 performing 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.
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 possible 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 testable, or falsifiable. In other words, it has to be an idea that you can support 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, 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 structures.
Discovery science of the 20th century
Although discovery science about the types of plants and animals on Earth had its heyday in the 1800s, discovery science about life on a level that’s too small to see with the naked eye is ongoing. One incredibly important project that employed modern discovery science is the Human Genome Project, which set out to map where each trait is found on the 46 human chromosomes.
Instead of traveling across the oceans to explore the world and catalog living things like the discovery scientists of 200 years ago, scientists from all over the world set out to explore the very tiny, but very complex, landscape of the 46 human chromosomes that contain the collection of all the genes found in humans. Each of the 25,000 genes they located provides information about inherited traits. The traits range from little things, such as whether you can curl your tongue or not, to truly important things, such as whether you have a genetic risk for developing breast cancer or cystic fibrosis. By finding out where genes are located, scientists can turn their attention to using this newfound information to develop hypotheses about cures and gene therapies.
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 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 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 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.
Any scientific experiment must have the ability to be duplicated because the “answer” the scientist comes up with (whether it supports or refutes 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.
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 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: The factor you want to test is an experimental variable (also called an independent variable).
Responding variables: The factor you measure is the responding variable (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.
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 variable. 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 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.
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 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 measurements 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.
One man’s error is another man’s starting point
In the early 1900s, a Russian researcher named A.I. Ignatowski fed rabbits a diet of milk and eggs. He found that the rabbits’ aortas developed the same kind of plaques that form in people with atherosclerosis. Ignatowski wasn’t ignorant, but he assumed that the atherosclerosis was caused by the proteins in the milk and eggs. He was wrong.
A younger researcher who was working in the same pathology department at the time, a Russian named Nikolai Anichkov, knew of Ignatowski’s work. Anichkov and some of his colleagues repeated Ignatowski’s study with one small change: They split the rabbits into three different groups. The first group was fed a supplement of muscle fluid, the second group was fed only egg whites, and the third group was fed only egg yolks. Only the yolk-eating rabbits developed plaques in their aortas. The young researchers ran the experiment again; this time they analyzed the atherosclerotic plaques to look for any concentrated chemical substances. In 1913, Anichkov and his colleagues discovered that cholesterol in the egg yolk was responsible for creating plaques in the aorta. Their discovery may not have been possible if Ignatowski had never conducted his experiment (or if he’d beaten them to the punch!).
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 prerace helps marathon runners improve their speed.
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 the validity of an experiment is referred to as statistical significance. Scientists analyze their data with statistics in order to determine whether the differences between groups are significant. If an experiment is performed repeatedly and the results are within a narrow margin, the results are said to be significant. In your experiment, if the race times for your friends were very similar within each group, so that pretty much all of your pasta-eating friends ran faster than your non-pasta-eating friends, then that two-minute difference actually meant something. But what if some pasta-eating friends ran slower than non-pasta-eating friends and one or two really fast friends in the pasta group lowered that group’s overall average? Then you might question whether the two minutes was really significant, or whether your two fastest friends just got put in the pasta group randomly.
Error: Science is done by people, and people make mistakes, which is why scientists always include a statement of possible sources of error when they report the results of their experiments. Consider the possible errors in your experiment. What if you didn’t specify anything about the content of the normal meals to your non-pasta-eating friends? After the race, you might find out that some of your friends ate large amounts of other sources of carbohydrates, such as rice or bread. Because your hypothesis was about the effect of carbohydrate consumption on marathon running, a few non-pasta-eating friends eating rice or bread would represent a source of error in your experiment.
Whether the scientist is right or wrong isn’t as important as whether he or she sets up an experiment that can be repeated by other scientists who expect to get the same result.
Seeing Science as the Constant Sharing of New Ideas
The knowledge gathered by scientists continues to grow and change slightly all the time. Scientists are continually poking and prodding at ideas, always trying to get closer to “the truth.” They try to keep their minds open to new ideas and remain willing to retest old ideas with new technology. Scientists also encourage argument and debate over ideas because the discussion pushes them to test their ideas and ultimately adds to the strength of scientific knowledge. Following are some of the facts about scientific ideas that illustrate how science is ever-evolving:
Today’s scientists are connected to scientists of the past because new scientific ideas are built upon the foundations of earlier work. For instance, a scientist working in a particular area of biology reads all the scientific publications he can that relate to his work to be sure he has the best understanding possible of what has already been done and what’s already known. That way, he can plan research that will advance the understanding in his field and add new knowledge to the scientific knowledge base.
Some scientific ideas are very old but still applicable today. Occasionally, new technology enables scientists to test old hypotheses in new ways, leading to new perspectives and changes in ideas. Case in point: Up until the 1970s, scientists looking through microscopes thought only two main types of cells made up living things. When scientists of the ’70s used new technology to compare the genetic code of cells, they realized that living things are actually made up of three main types of cells — two of the types just happen to look the same under a microscope. Of course, old ideas aren’t always proved completely wrong — for example, scientists still recognize the two structural types of cells — but big ideas can shift slightly in the face of new information.
When many lines of research support a particular hypothesis, the hypothesis becomes a scientific theory. A scientific theory is an idea that’s supported by a great deal of evidence and hasn’t been proven false despite repeated tests. Scientific theories don’t change as often as scientific hypotheses due to the significant evidence backing them up, but even scientific theories can shift in light of new evidence. Ideally, scientists always keep an open mind and look at new evidence objectively.
Conflicting reports mean science is working
Sure, it’s aggravating when the media reports conflicting findings — such as margarine is better for your cholesterol level but it also produces harmful fatty acids that contribute to heart disease — but conflicting news reports are a sign that science is alive and well. For example, when scientists figured out that high cholesterol levels contributed to heart disease, they correctly determined that a product created from vegetable oil rather than animal fat — in other words, margarine rather than butter — was a healthier choice if you were trying to lower your cholesterol level.
But scientists don’t just leave things alone. They keep wondering, questioning, and pondering. They’re curious guys and gals, which is why they kept researching margarine. Recently, they discovered that when margarine breaks down, it releases trans fatty acids, which were found to be harmful to the heart and blood vessels. So, margarine has bad aspects that may outweigh the good. Yes, this can make decisions at the grocery store more confusing, but it can also lead to better health for everyone. Case in point: After the information about trans fatty acids became known, food companies started developing new ways to make margarine and other foods so that they don’t contain trans fatty acids.
Tracking Down Scientific Information
Scientists publish their work in part because scientists in different areas of the world may be trying to answer the same questions and could benefit from seeing how someone else approached the problem. The other part is that if scientists didn’t put their work out there, flaws and all, no one would ever know the work was being done. The sections that follow provide an overview of the different sources scientists use to communicate with each other (and the rest of the world).
Journals: Not just for recording dreams
Hundreds of scientific journals cover every topic and niche imaginable in the fields of biology, chemistry, physics, engineering, and so on. They’re published by numerous organizations, including professional groups, universities or medical centers, and medical and scientific publishing companies. Regardless of their subject matter or where they come from, all scientific journals have one common characteristic: They’re all considered a primary source of scientific information, meaning they contain a full description of the original research written by the original researchers.
Anyone researching a topic, whether he’s a student or a scientist, consults the journals first. They contain the original research papers, which means you can always find the latest information in a specific field in a journal. The research papers are written following the scientific style of anabstract (summary). First, there’s a statement of the hypothesis. Next come a description of the materials used; a description of how the experiment was designed and performed; and the results of the experiment, including raw data, graphs, and tables. Finally, the paper notes the author’s conclusions and errors that occurred during the experiment(s).
Scientific journals undergo a peer-review process to help ensure the reliability of published scientific information. Here’s how the process works: The editor of a scientific journal sends a research paper out to other scientists who work in the same field as the scientist(s) who wrote the paper to examine and comment on the work. They’re tasked with making sure the science is thorough and that the research adds to the scientific knowledge base. The editor then decides whether or not to publish the paper based on the other scientists’ comments. If the reviewers’ and editor’s stringent criteria aren’t meant, the research paper can’t be published in the journal.
Although many scientific journals are available online, you may not be able to access the articles without paying a fee. However, if you’re a student at a college or university, your school library may subscribe to various scientific journals. Ask a member of the library staff whether the school subscribes to any scientific journals and, if so, how you can access them via the library’s computers.
Textbooks: A student’s go-to source
Textbooks. Whether you love ’em or hate ’em (or could care less about ’em), textbooks are considered secondary sources of scientific information, meaning they compile or discuss information taken from primary sources. Secondary sources aren’t usually written by the original researchers. They present the knowledge base of a specific topic or field at a certain point in time, which makes them a good source to turn to for the history of a topic, basic facts about a certain subject, and summaries of important research that has furthered the field.
The popular press: Not always accurate
The popular press — regular ol’ newspapers, magazines, and television and radio programs, are considered tertiary sources (meaning they’re twice removed from the original source of information). The popular press provides information, of course, but the validity of that information isn’t guaranteed. There’s always a chance that the journalist doing the reporting may have misunderstood the scientist’s research or something he said. It’s like that old childhood game where the information given to the first person is usually changed by the time it gets relayed to the last person.
You’re always better off citing an article in a journal or textbook before one from a major media outlet.
The Internet: A wealth of information, not all of it good
Lots of scientific information is available on the Internet, and much of it is available for free. The trick is distinguishing the good stuff from the bad. To find good-quality scientific information:
Visit government Web sites. These Web sites end in .gov. Some primary literature is available on government Web sites, but even the secondary literature is usually of high quality. If you use the advanced search feature on your web browser, you should be able to restrict your searches to the types of domains you’re interested in.
Surf university Web sites. These Web sites end in .edu. Some university scientists post copies of their papers, which are examples of primary literature, and others post good-quality lecture notes and articles. (Better yet, if you’re a student at a college or university, access the primary literature — scientific journals — through your school library’s subscription service.)
Be careful when visiting organization Web sites. These Web sites end in .org. Large organizations with good reputations, such as the American Heart Association, usually have good-quality secondary information on their sites; they may even post links to primary sources. However, smaller organizations that don’t have an established reputation aren’t good sources for scientific information.
Avoid commercial Web sites (those with .com endings) when you’re looking for scientific information. People and organizations operating commercial sites are trying to sell you something. They have an agenda of their own, which means you can’t trust that they’re completely unbiased. The information they present may be one-sided or not accepted as reliable by the scientific community.