In AP Biology, hypothesis questions can be make-or-break moments on the FRQ section. They test your ability to think scientifically, make predictions based on given data, and articulate your reasoning clearly.
If you’ve ever lost points because your hypothesis was “too vague” or “unsupported,” this guide is for you.
We’ll cover:
- The AP Bio definition of a hypothesis
- What graders look for
- A step-by-step method to write high-scoring hypotheses
- Common mistakes to avoid
- Example responses
Understanding Hypotheses in AP Biology
A hypothesis is a testable statement that predicts the outcome of an experiment based on a specific rationale.
In the AP Biology context, the key elements are:
- Specificity – clear and focused on one measurable outcome
- Testability – something that can be confirmed or disproven with data
- Biological reasoning – backed by established concepts or mechanisms
Example:
If the amount of light available to a plant is increased, then the rate of photosynthesis will increase, because more photons will excite electrons in the chlorophyll pigments, driving the light reactions.
What the AP Scoring Rubric Looks For
From College Board past FRQ rubrics, high-scoring hypotheses typically:
- Address the independent and dependent variables directly
- Include a clear prediction about the relationship
- Provide a biological explanation supporting the prediction
Partial credit is often given if a prediction is stated but reasoning is missing — but full credit requires both.
Step-by-Step Method to Writing a High-Scoring Hypothesis
- Identify the Variables
- Independent Variable: the factor you change (e.g., light intensity)
- Dependent Variable: the factor you measure (e.g., photosynthetic rate)
- Make a Clear Prediction
Use “If…then…” or “An increase in…will result in…” structure. - Include Biological Reasoning
Reference relevant processes (enzymes, cellular respiration, diffusion, etc.). - Avoid Overcomplication
Keep it one sentence if possible, two at most.
Common Mistakes to Avoid
- Being Too Vague
❌ “Plants grow better with more light.”
✅ “Increasing light intensity will increase the rate of photosynthesis in Elodea plants because higher photon input accelerates light-dependent reactions.” - Skipping the Reasoning
Without the “because” part, your hypothesis is incomplete. - Predicting Without Variables
Always tie your prediction to measurable factors.
Example High-Scoring Hypotheses
Lab Scenario: You are testing the effect of pH on enzyme activity for catalase.
- If the pH of the solution moves away from the enzyme’s optimum (pH 7), then the rate of hydrogen peroxide breakdown will decrease because changes in pH alter the shape of the enzyme’s active site, reducing substrate binding efficiency.
Lab Scenario: You are testing the effect of temperature on respiration rate in crickets.
- Increasing temperature will increase the respiration rate of crickets up to an optimal point because higher temperatures accelerate enzyme-mediated metabolic reactions, until denaturation occurs.
Practice Tip – Using Past FRQs
The best way to improve is by reviewing past AP Biology FRQs from the College Board.
- Search “AP Biology Free Response Questions” on the official AP Central site.
- Write hypotheses for old experimental design questions.
- Compare with scoring guidelines to see what graders awarded full credit.
FAQ – AP Biology Hypothesis Questions
Q: Should I always use “If…then…” format?
A: Not required, but it can help structure your thought process.
Q: How long should my hypothesis be?
A: Usually one sentence, but two is fine if you need to clarify reasoning.
Q: Can I earn points for just stating a correct prediction?
A: Sometimes partial credit is awarded, but full points require reasoning.
Final Call to Action
High-scoring AP Biology hypotheses are precise, testable, and rooted in biology. They don’t just predict — they explain.
At RevisionDojo, we help students master FRQs through guided practice and feedback based on official rubrics. Whether you’re aiming for a 3 or pushing for that perfect 5, our targeted strategies will sharpen your scientific writing skills.
