Cracking the AP Biology Exam


The Free-Response Questions


We briefly discussed the essay portion of the test in Chapter 1. We saw that Section II of the AP Biology Exam consists of four essays, one or more of which is divided into several parts. One question will come from Molecules and Cells, another question will come from Heredity and Evolution, and two questions will come from Organisms and Populations. Questions might cover more than one area. You’ll have a 10-minute reading period followed by a 90-minute period to complete these essays. The essays are equally weighted, and together they count for 40 percent of your final grade. The highest score you can get on an essay is 10, although there are multiple ways of getting maximum credit. Now, let’s look at the essays in greater detail.

At first glance, most students panic when they look at the essay questions on the test. They wonder how they are going to write four well-thought-out essays, complete with figures and graphs, in 90 minutes! They believe this must be the toughest part of the test. Well, they’re wrong. Believe it or not, this is the part of the test on which you can actually shine. Why? Because you’re no longer limited to multiple-choice questions where there’s only one right answer. This time, you can dazzle the test reviewers with your vast knowledge of biology (especially after having read this book). We’ve come up with six tips that will help you ace the essay portion of the test.


ETS gives you 10 minutes to read the questions and organize your thoughts before you begin writing. If you use these 10 minutes wisely, you can breeze your way through the essays. The first thing you should do is take less than a minute to skim all of the questions and put them into your own personal order of difficulty from easiest to toughest. Once you’ve decided the order in which you will answer the questions (easiest first, hardest last), you can begin to formulate your responses. Your first step should be a more detailed assessment of each question.

The most important advice we can give you is to read each question at least twice. As you read the question, focus on key words, especially “direction words.” Almost every essay question begins with a direction word. Some examples of direction words are discuss, define, explain,describe, compare, and contrast. If a question asks you to discuss a particular topic, you should give a viewpoint and support it with examples. If a question asks you to compare two things, you should discuss how the two things are similar. On the other hand, if the question asks you to contrast two things, you need to show how these things are different.

Many students lose points on their essays because they either misread the question or fail to do what’s asked of them.


Your next objective during the 10-minute preview should be to organize your thoughts.

Once you’ve read the questions, you need to brainstorm. Jot down as many key terms and concepts—the “hot buttons” we mentioned in Chapter 1—as you can. Don’t forget, the test reviewers assign points on the basis of these key concepts: For each one that you mention and/or explain, you get a point.

How many do you need? You won’t need all of them, that’s for sure. However, you will need enough to get you the maximum number of points for that question. Most of these you can pull directly from your reading in this book. Remember the “Key Words” lists in each chapter of this book? They are essential to your preparation for this part of the test. Use your word associations to generate thorough lists. Once you’ve come up with as many different hot buttons as possible, you’re ready to leap into your outline.

Don’t spend more than about 2 minutes per question brainstorming. Once your 10-minute reading period is up you should be ready to start writing your essays.


Have you ever written yourself into a corner? You’re halfway through your essay when you suddenly realize that you have no idea whatsoever where you’re going with your train of thought. To avoid this (and the panic that accompanies it), take a few minutes to draft an outline.

Your outline should incorporate as many of the hot buttons as you need in order to maximize your score. In other words, if they ask for two examples, choose only those two with which you are most comfortable. In your outline, make notes about the crucial points to mention with regard to each topic or key word. Once your outline is complete, you’re ready to move on to writing the actual essay.

All of this preparation may seem time-consuming. However, it should take no more than four or five minutes per essay. What’s more, it will greatly simplify the whole essay-writing process. So while you lose a little time at the outset, you’ll more than make up for it when it comes time to actually write your answer.

Remember: Unless you’re aiming to score a perfect 5, there’s no reason to do all the essays. If you’re uncertain about how many you need to reach your score, look back at the pacing chart in Chapter 1.


Now you can use your outline to write your essay. Most students can come up with key terms or phrases that concern a particular biology topic. What separates a high-scoring student from a low-scoring student is how the student develops his or her thoughts on each essay. Besides giving the hot buttons, you’ll need to elaborate on your thoughts and ideas. For example, don’t just throw out a list of terms that pertain to meiosis and mitosis (like synapsis, crossing-over, and gametes). Go one step further. Make sure you mention the significance of meiosis (i.e., it produces genetic variability). This extra piece of information will earn you an extra point.

Generally, you’ll need to write about two to four paragraphs, depending on the number of parts contained in each essay question. In addition, be sure to give the appropriate number of examples for each essay. If the question asks for three examples, give only three examples. If you present more than is required, the test reviewers won’t even read them or count them toward your score. The bottom line is this: Stick to the question.


The more parts there are to an essay question, the more important it is to pace yourself. On each essay, you’re better off writing a little bit for each part than you are spending all your time on any one part of a question. Why? Even if you were to write the perfect answer to one part of a question, there’s a limit to the number of points the test reviewers can assign to that part. Moreover, by writing a separate paragraph for each section, you make the test grader’s job that much easier. When test readers have an easy time reading your essay, they’re more likely to award points: It comes across as clearer and more organized. Readers have also requested that students label each part of their essay answers, so write “Part a”, “Part b”, and so on, accordingly in your response.

Finally, don’t spend too much time writing a fancy introduction. You won’t get brownie points for beautifully written openings like, “It was the best of experiments, it was the worst of experiments.” Just leap right into the essay. And don’t worry too much about grammar or spelling errors. Your grammar can hurt only if it’s so bad that it seriously impairs your ability to communicate.


Since one of the essay questions will be experimentally based, you’ll need to know how to design an experiment. Most of these questions require that you present an appropriately labeled diagram or graph. Otherwise, you’ll only get partial credit for your work.

There are two things you must remember when designing experiments on the AP Biology Exam: (1) Always label your figures, and (2) include controls in all experiments. Let’s take a closer look at these two points.

Know How to Label Diagrams and Figures

Let’s briefly discuss the important elements in setting up a graph. The favorite type of graph on the AP Biology Exam is the coordinate graph. The coordinate graph has a horizontal axis (x-axis) and a vertical axis (y-axis).

The x-axis usually contains the independent variable—the thing that’s being manipulated or changed. The y-axis contains the dependent variable—the thing that’s affected when the independent variable is changed.

Now let’s look at what happens when you put some points on the graph. Every point on the graph represents both an independent variable and a dependent variable.

Once you draw both axes and label the axes as x and y, you can plot the points on the graph. In Chapter 1, we saw an essay question that included a part about enzymes and the influence of various factors on enzyme activity. Let’s look at the question again.

1. Enzymes are biological catalysts.

a. Relate the chemical structure of an enzyme to its catalytic activity and specificity.

b. Design an experiment that investigates the influence of temperature, substrate concentration, or pH on the activity of an enzyme.

c. Describe what information concerning enzyme structure could be inferred from the experiment you have designed.

For now, let’s discuss only part b, which asks us to design an experiment. Let’s set up a graph that shows the results of an experiment examining the relationship between pH and enzyme activity. Notice that we’ve chosen only one factor here, pH. We could have chosen any of the three. Why did we choose pH and not temperature or substrate concentration? Well, perhaps it’s the one we know the most about.

What is the independent variable? It is pH. In other words, pH is being manipulated in the experiment. We’ll therefore label the x-axis with pH values from 0 through 14.

What is the dependent variable? It’s the enzyme activity—the thing that’s affected by pH. Let’s label the y-axis “Rate of Reaction.” Now we’re ready to plot the values on the graph. Based on our knowledge of enzymes, we know that for most enzymes the functional range of pH is narrow, with optimal performance occurring at or around a pH of 7.

Now you should interpret your graph. If the pH level decreases from a neutral pH of 7, the reaction rate of the enzyme will decrease. If the pH level increases, the rate of reaction will also decrease. Don’t forget to include a simple explanation of your graph.

Include Controls in Your Experiments

Almost every experiment will have at least one variable that remains constant throughout the study. This is called the control. A control is simply a standard of comparison. What does a control do? It enables the biologist to verify that the outcome of the study is due to changes in the independent variable and nothing else.

Let’s say the principal of your school thinks that students who eat breakfast do better on the AP Biology Exam than those who don’t eat breakfast. He gives a group of 10 students from your class free breakfast every day for a year. When the school year is over, he administers the AP Biology Exam and they all score brilliantly! Did they do well because they ate breakfast every day? We don’t know for sure. Maybe the principal handpicked the smartest kids in the class to participate in the study.

In this case, the best way to be sure that eating breakfast made a difference is to have a control group. In other words, he would need to pick students in the class who never eat breakfast and follow them for a year. At the end of that year, he could send them in to take the AP Biology Exam. If they do just as well as the group that ate breakfast, then we can probably conclude that eating breakfast wasn’t the only factor leading to higher AP scores. The group of students that didn’t eat breakfast is called the control group because those students were not “exposed” to the variable of interest—in this case, breakfast.

Now that we’ve covered the important points on how to tackle the essay section, let’s see if you can write a good essay using the techniques we’ve just discussed. Take 22 minutes to write a response to the sample essay.

1. All organisms need nutrients to survive. Angiosperms and vertebrates have each developed various methods to obtain nutrients from their environment.

a. Discuss the ways angiosperms and vertebrates procure their nutrients.

b. Discuss two structures used for obtaining nutrients among angiosperms. Relate structure to function.

c. Discuss two examples of symbiotic relationships that have evolved between organisms to obtain nutrients.