One of the most intimidating AP Biology FRQ types is the “Design an Experiment” question. It requires more than memorization — you must demonstrate scientific thinking, a solid grasp of experimental design principles, and clear communication.
RevisionDojo has broken this question type into a step-by-step strategy so you can confidently tackle it on test day.
1. Understand What College Board Is Looking For
The experimental design FRQ usually asks you to:
- Develop a testable hypothesis.
- Identify independent and dependent variables.
- Describe a control group and constants.
- Outline methods for data collection.
- Predict expected results.
They want to see that you can think like a scientist — asking a focused question, setting up a valid experiment, and explaining how the results will be interpreted.
2. Break Down the Prompt
When you see an experimental design FRQ, do this immediately:
- Underline the main biological process (e.g., photosynthesis, enzyme activity, population growth).
- Circle the task words — “design,” “propose,” “describe,” “predict.”
- Identify the specific relationship they want you to test.
3. Start with a Hypothesis Statement
Your hypothesis should:
- Be testable and specific.
- Include both variables.
- Predict the direction of the effect if possible.
Example:
If the concentration of sucrose in a solution increases, then the rate of osmosis in potato cells will increase, because water will move from areas of low solute concentration to high solute concentration.
4. Identify Your Variables
- Independent Variable (IV): The factor you change.
- Dependent Variable (DV): The factor you measure.
- Control Group: The group used for comparison (often no treatment or a standard condition).
- Constants: Factors kept the same for all groups.
5. Outline Your Procedure Clearly
Write in a logical sequence that another scientist could follow. Include:
- Sample size and replication.
- Time frame of data collection.
- Specific measurements or tools (e.g., “measure absorbance at 550 nm using a spectrophotometer”).
Pro Tip from RevisionDojo: Don’t waste words — the scoring rubric rewards completeness, not flowery language.
6. Include Data Collection and Analysis
- Explain how you’ll measure the DV.
- Mention statistical tests if relevant (Chi-square, t-test).
- Describe how you’ll present data (table, graph).
7. Predict Expected Results
This step is often worth 1–2 easy points:
- Draw a quick sketch of your expected graph.
- Describe the trend you expect and explain why it supports or refutes the hypothesis.
8. Avoid Common Mistakes
- Forgetting the control group.
- Not stating constants.
- Writing vague procedures (“measure plant growth” — without saying how you’ll measure it).
- Using a hypothesis that doesn’t connect to the question.
9. Practice with Real College Board FRQs
Here are some past experimental design questions to try:
- 2017 #8: Effect of pH on enzyme activity.
- 2015 #7: Effect of temperature on cellular respiration in germinating seeds.
- 2013 #5: Effect of salinity on plant germination.
You can find all past AP Biology FRQs and scoring rubrics on the College Board AP Central site.
10. Quick AP Bio Experimental Design Checklist
Before moving on to the next question, make sure you’ve:
- Written a clear, testable hypothesis.
- Identified IV, DV, controls, and constants.
- Described a replicable procedure.
- Explained data collection and analysis.
- Predicted and interpreted results.
FAQ – Design an Experiment AP Biology FRQs
1. How many points are these FRQs worth?
Usually 4–6 points, depending on the complexity.
2. Can I use bullet points for my procedure?
Yes — and it’s often better for clarity.
3. Do I need to mention error sources?
Not unless the question asks for them, but noting limitations can strengthen your explanation.
4. Is drawing a graph necessary?
If the prompt asks for results, a quick labeled graph can help earn points.
RevisionDojo Pro Tip: Treat experimental design FRQs as if you’re writing instructions for another AP Biology student to replicate your work. If they could follow your steps and get valid results, you’ve likely earned full points.
