Scientific argumentation: claims, evidence, reasoning and predictions

What the exam asks

On the AP Biology exam, argumentation is never tested in isolation; it is embedded in experimental scenarios, models, and data sets across all eight units.

• In Section I (Multiple Choice): You will be asked to select which statement best justifies a claim, which piece of data supports a researcher’s hypothesis, or what will happen to a system if a specific component is disrupted.
• In Section II (Free Response): Question 1 (Part D), Question 2 (Part D), Question 3 (Parts C and D), Question 4 (Parts C and D), and Question 6 (Parts C and D) directly award points for predicting the effects of a change, evaluating a hypothesis with data, and justifying your claims with biological reasoning.

Core ideas

The CER (Claim–Evidence–Reasoning) Framework

A complete scientific argument has three distinct components. On free-response questions, a claim such as a prediction often earns one point and its justification (evidence plus reasoning together) earns another, so leaving out any of the three can cost you a point:

1. Claim: A declarative statement that directly answers the prompt or states the outcome of an experiment. It does not include the “because.”
2. Evidence: Specific data from a table or graph (including numbers, trends, or whether $\pm 2\,SE_{\bar{x}}$ error bars overlap; these bars reach two standard errors of the mean above and below each mean) or a biological principle, concept or process, including facts given in the prompt.
3. Reasoning: The logical bridge that explains how or why the evidence supports the claim, using underlying biological principles (such as hydrogen bonding, protein folding, or natural selection).

Mastering AP Task Verbs

Free-response prompts put task verbs in bold. Each verb tells you the exact depth of answer required to earn the point: