What’s on the AP Biology Exam? Topics & Question Types Explained
TLDR
The exam covers 8 units, with Natural Selection, Cellular Energetics, and Gene Expression carrying the most weight.
Section I = 60 multiple-choice questions (MCQs) in 90 minutes, 50% of the score.
Section II = 6 free-response questions (FRQs) in 90 minutes, 50% of the score.
Questions emphasize data analysis, experimental design, and model application.
Key formulas: water potential, chi-square, Hardy–Weinberg, population growth, Gibbs free energy.
👉 Download our free AP Biology Formula Sheet
Introduction
If you’re preparing for AP Biology, one of the biggest questions is: what’s actually on the exam? Many students know it’s a challenging test, but few understand the exact balance of topics, skills, and question types that the College Board uses.
This guide breaks down the 8 units, their weightings, the kinds of questions you’ll face, and the formulas you need to know. By the end, you’ll know exactly how to focus your study time for maximum results.
The 8 Units and Their Weighting
The AP Biology exam is built around 8 curriculum units. Each unit contributes a specific percentage to the multiple-choice section:
Unit 1: Chemistry of Life (8–11%) — Structure of water, macromolecules, and bonding basics.
Unit 2: Cell Structure and Function (10–13%) — Membranes, organelles, surface area-to-volume ratios.
Unit 3: Cellular Energetics (12–16%) — Enzymes, photosynthesis, cellular respiration, ATP yield.
Unit 4: Cell Communication and Cell Cycle (10–15%) — Signal transduction, checkpoints, mitosis, feedback systems.
Unit 5: Heredity (8–11%) — Mendelian genetics, probability, chi-square analysis.
Unit 6: Gene Expression and Regulation (12–16%) — DNA/RNA, transcription, translation, operons, regulation.
Unit 7: Natural Selection (13–20%) — Hardy–Weinberg equilibrium, evolutionary theory, fitness.
Unit 8: Ecology (10–15%) — Population growth, energy flow, nutrient cycles, ecosystems.
💡 Tutor Tip: Our Brown University tutor says, focus extra time on Units 3, 6, and 7 — together they can make up almost half of the exam.
Question Types You’ll Face
Section I: Multiple Choice
60 questions in 90 minutes (50% of the exam).
Includes stand-alone questions and stimulus-based sets with graphs, tables, or experiment descriptions.
Tests both recall and analysis skills.
Section II: Free Response
6 questions in 90 minutes (50% of the exam).
2 long FRQs (worth 9 points each): often experimental design, data interpretation, and graphing.
4 short FRQs (worth 4 points each): conceptual analysis, model-based questions, and data interpretation.
Math & Formulas
The exam expects you to apply formulas — not just memorize them. Expect questions on water potential, chi-square, Hardy–Weinberg, and population growth.
Skills Tested Beyond Content
The exam isn’t just about memorization. It tests whether you can think and write like a biologist:
Analyze and interpret data — graphs, tables, charts.
Apply models — such as feedback loops, Hardy–Weinberg, or logistic growth.
Design experiments — identify variables, controls, and expected outcomes.
Explain concepts clearly — write in complete sentences with evidence and reasoning.
💡 Tutor Tip: When practicing FRQs, always structure answers as Claim → Evidence → Reasoning. This matches how graders award points.
How to Study Based on What’s Tested
Prioritize high-weight units (Natural Selection, Gene Expression, Cellular Energetics).
Practice MCQs in sets of 15–20 with a timer to build speed.
Write at least 2 FRQs per week, grading yourself against the official rubrics.
Review labs and experimental design since these frequently show up on FRQs.
Use formula-based practice so you’re ready to apply equations quickly under pressure.
The AP Biology exam rewards students who know not only the content but also how the exam is built. By focusing on the highest-weight units, practicing FRQs, and mastering formula applications, you’ll be ahead of the curve.
