How to Answer “Design an Experiment” AP Biology FRQs | RevisionDojo

Read the prompt carefully and restate the biological relationship being tested.

Step 2 – Define your variables

• IV – The factor you will manipulate.
• DV – The factor you will measure.

Step 3 – Choose an appropriate control group

The control should be identical to the experimental group except for the IV.

Step 4 – Write a clear procedure

Be specific — vague statements like “measure growth” won’t earn points unless you say how (e.g., “measure plant height in cm every 24 hours for 10 days”).

Step 5 – Explain the expected results

Tie your prediction back to a biological principle (e.g., enzyme activity, osmosis, photosynthesis rates).

4. Example AP Biology Experimental Design Question

Prompt: A student hypothesizes that increasing light intensity will increase the rate of photosynthesis in Elodea plants.

High-Scoring Response:

• Hypothesis: If light intensity increases, then the rate of photosynthesis will increase until it reaches a saturation point.
• IV: Light intensity (lux).
• DV: Rate of oxygen bubble production per minute.
• Control Group: Plants kept in low light (100 lux).
• Constants: Temperature, plant species, water pH, carbon dioxide levels.
• Procedure: Place Elodea in water-filled beakers under varying light intensities (100, 500, 1000, 1500 lux). Measure number of oxygen bubbles produced in 5 minutes. Repeat 3 times for each light level.
• Expected Results: Oxygen production increases from 100 to 1000 lux, then levels off due to enzyme saturation in the Calvin cycle.

5. Common Mistakes to Avoid

• Forgetting constants – Missing these can cost easy points.
• No control group – Without it, results are meaningless.
• Vague measurements – Always include units and methods.
• Not connecting to biology – Predictions without explanation lose points.

6. Where to Practice Experimental Design FRQs

• College Board AP Biology FRQ Archive – Look for past questions labeled “design an experiment” or “propose an investigation.”
• AP Classroom – Question Bank includes experimental design practice.
• Barron’s and Princeton Review – Both have dedicated experimental design drills.

7. Scoring Tips from College Board Rubrics

• Be specific – Generic answers rarely score well.
• Use complete sentences – Avoid bullet-only answers unless clearly labeled with all parts.
• Answer every part – Missing one part (e.g., constants) can drop you from full credit.

FAQ – Experimental Design FRQs

Q: Do I need to include a graph?
A: Only if the question asks for one — otherwise, focus on written details.

Q: How long should my answer be?
A: Quality matters more than length, but most full-credit responses are 1–2 well-structured paragraphs.

Q: Should I always repeat the hypothesis?
A: Yes — it helps organize your answer and is almost always worth points.

Final Takeaway

Experimental design FRQs test your ability to think scientifically. The best way to prepare is by practicing with real College Board questions and getting familiar with rubrics. By mastering how to clearly define variables, controls, and expected results, you’ll be ready to score high on this challenging FRQ type.

At RevisionDojo, we recommend doing at least one experimental design FRQ per week in the 3 months leading up to the exam — it’s one of the best ways to build confidence and earn points on test day.