AP Biology · Exam guide
AP Biology Long Free-Response Question Explained: Interpreting and Evaluating Experimental Results
The first long question on the AP Biology exam describes an experiment and asks you to interpret and evaluate its results. It is worth 9 points, and it is the most predictable question on the exam: the same skills appear every year, in the same order. The data below are made up for practice.
What the question asks you to do
| Skill | What it sounds like in the question |
|---|---|
| Identify parts of the experiment | Identify the independent variable, the dependent variable, the control group, or a variable that was held constant. |
| Describe the data | Describe the trend in the results, using numbers from the table or graph. |
| Explain with biology | Explain how or why the result occurred, using a biological concept. |
| Calculate | Calculate a mean, a rate, a percent change, or a standard error from the data. |
| Evaluate | Decide whether the data support a claim, and justify your decision with evidence. |
| Predict or revise | Predict the result of a change, or say how you would improve the design. |
A made-up experiment
A student grew bean seedlings for 14 days under red light and under blue light, with five plants in each group and all other conditions kept the same. Heights in centimeters: red light 12, 14, 13, 15, 11; blue light 8, 9, 7, 10, 6.
Identify the parts
It does not say whether it is the independent or the dependent variable.
It names both variables and gives something that was controlled.
Calculate
Mean height under red light is (12 + 14 + 13 + 15 + 11) divided by 5, which is 13.0 cm. Mean height under blue light is (8 + 9 + 7 + 10 + 6) divided by 5, which is 8.0 cm. In both groups the standard deviation is about 1.58 cm, so the standard error is 1.58 divided by the square root of 5, about 0.71 cm. Two standard errors is about 1.4 cm.
Show the formula, the substitution, and the answer with units. On the exam, a mean and a standard error are the calculations you should expect to be able to do.
Evaluate the claim
Question: Evaluate the claim that blue light slows growth compared with red light.
It gives a direction but no numbers and no use of the error values.
It uses the means and the error values to decide, and it states a conclusion.
Explain with biology
It links the independent variable to a biological process and to the dependent variable.
Common mistakes
- Naming a variable without saying whether it is independent or dependent.
- Describing a trend without numbers from the table.
- Saying the data "prove" something. Data can support or fail to support a claim.
- Ignoring the error values when asked to evaluate a difference.
- Giving a biological fact that has no link to the result in the question.
Frequently asked questions
How many points is the first long question worth?
Nine points. It is one of two long questions on the free-response section.
Do I need to memorize the formulas for standard error?
The exam provides a formula sheet, but you should practice using it so you can set up the calculation quickly.
How do I read error bars?
If the intervals of two groups do not overlap, the difference is probably meaningful. If they overlap a lot, you cannot say the groups differ.
How long should I spend on it?
Plan on about 25 minutes, since the long questions have more parts than the short ones.
Where can I find the official scoring rules?
Exam formats change a little from year to year, so check the current course and exam description on the College Board site before test day.
Keep practicing
Every unit in the AP Biology course ends with a quiz of 15 multiple-choice questions and 5 short free-response questions, with a writing space that scores against the four-point rubric and a model 4 out of 4 response to compare against. These free lessons also build the skills the free-response section tests:
See the AP Biology course Free lessons and lesson list
Other free-response guides:
- AP Biology FRQ Guide: The Six Free-Response Questions and the 4-Point Rubric
- AP Biology Graphing Question Explained: How to Construct a Graph and Interpret the Data
- AP Biology Short Free-Response Questions Explained: The Four Types and the 4-Point Rubric
AP is a registered trademark of the College Board, which is not affiliated with and does not endorse this site. This guide is our own explanation of the question types and scoring. For the official scoring guidelines, see the College Board.