AP Biology (College Board): complete guide to the eight units, the science practices and the exam
A complete guide to College Board AP Biology. Covers the eight units (from chemistry of life to ecology), the four big ideas, the six science practices, how Section I (multiple choice) and Section II (free response questions) work, the math and statistics demand, and how to study each unit for a 5.
College Board AP Biology is designed to be the equivalent of a two-semester, introductory college biology course for majors. The course is built on four big ideas and six science practices, and the content is organized into eight units. There is no coursework, but laboratory investigation and quantitative skills are examined directly in both sections of the exam. This page is the index: below is a map of the eight units, the exam structure, and how to study each one. This release covers Units 1 to 4 in full.
The eight AP Biology units
The College Board organizes the content into eight units. Each carries an exam weighting (the share of multiple-choice questions it tends to contribute).
- Unit 1 Chemistry of Life (8 to 11%)
- The structure and properties of water and hydrogen bonding, the elements of life, the four classes of biological macromolecule (carbohydrates, lipids, proteins, nucleic acids), how monomers are joined and broken, the directionality and structure-function relationships of polymers, and the structure of DNA and RNA.
- Unit 2 Cell Structure and Function (10 to 13%)
- Subcellular components and their functions, the structure-function relationship in cells, the surface-area-to-volume ratio, the fluid-mosaic plasma membrane, selective permeability, passive and active transport, facilitated diffusion, tonicity and osmoregulation, cell compartmentalization, and the endosymbiotic origin of mitochondria and chloroplasts.
- Unit 3 Cellular Energetics (12 to 16%)
- Enzymes, cellular energy, photosynthesis, cellular respiration, and the regulation of metabolic pathways.
- Unit 4 Cell Communication and Cell Cycle (10 to 15%)
- Cell signalling, signal transduction, feedback, and the cell cycle and its regulation.
- Unit 5 Heredity (8 to 11%)
- Meiosis, Mendelian genetics, non-Mendelian inheritance, environmental effects, and chromosomal inheritance.
- Unit 6 Gene Expression and Regulation (12 to 16%)
- DNA and RNA structure, replication, transcription and translation, gene regulation, mutations, and biotechnology.
- Unit 7 Natural Selection (13 to 20%)
- Natural selection, evidence for evolution, the Hardy-Weinberg principle, speciation, extinction, and the origin of life.
- Unit 8 Ecology (10 to 15%)
- Responses to the environment, energy flow, population ecology, community ecology, biodiversity, and the disruption of ecosystems.
This release now covers all eight units in full.
Exam structure
The AP Biology exam is 3 hours and has two equally weighted sections. A calculator is allowed throughout, and a formula and equations sheet (including the chi-square formula and critical-value table) is provided.
- Section I, multiple choice - 60 questions, 1 hour 30 minutes, 50%. Discrete questions and question sets, many built on data, graphs, diagrams or models.
- Section II, free response - 6 questions, 1 hour 30 minutes, 50%. Two long FRQs (one on interpreting and evaluating experimental results, including a statistical or graphing task; one on analyzing model or visual representations) and four short FRQs.
The free-response questions are written from the six science practices, so they ask you to explain concepts, interpret and create visual models, design and refine experiments, describe and represent data, run statistical tests, and construct evidence-based arguments using AP task verbs (Describe, Explain, Identify, Calculate, Justify, Predict, Evaluate, Construct).
How to study AP Biology
AP Biology rewards conceptual depth, structure-to-function reasoning, and confident data and statistics handling.
- Work from the Course and Exam Description. Each topic (for example 1.4 Properties of Biological Macromolecules) maps to specific learning objectives and essential knowledge statements that exam questions are written from.
- Learn the science practices, not just the content. Practice explaining, modelling, designing experiments, and arguing from evidence, because the FRQs are scored on these skills.
- Master the quantitative toolkit. Chi-square, standard error and error bars, Hardy-Weinberg, water potential, surface-area-to-volume ratio and rates all recur.
- Connect topics to the four big ideas. Examiners reward answers that tie a structure or process to evolution, energetics, information, or systems interactions.
- Rehearse the FRQ format. Time yourself on long and short free-response questions and align every claim with evidence and reasoning.
The units, topic by topic
Each topic has a Course-and-Exam-Description-level answer page with worked exam questions and cross-links, plus an overview guide and quiz. Browse the set at /ap/biology/syllabus. This release covers all eight units in full:
- Unit 1: structure of water and hydrogen bonding, elements of life, introduction to biological macromolecules, properties of biological macromolecules, structure and function of biological macromolecules, nucleic acids.
- Unit 2: cell structure: subcellular components, cell structure and function, cell size, plasma membranes, membrane permeability, membrane transport, facilitated diffusion, tonicity and osmoregulation, mechanisms of transport, cell compartmentalization, origins of cell compartmentalization.
- Unit 3: enzyme structure, enzyme catalysis, environmental impacts on enzyme function, cellular energy, photosynthesis, cellular respiration.
- Unit 4: cell communication, introduction to signal transduction, signal transduction pathways, feedback, cell cycle, regulation of the cell cycle.
- Unit 5: meiosis, meiosis and genetic diversity, Mendelian genetics, non-Mendelian genetics, environmental effects on phenotype, chromosomal inheritance.
- Unit 6: DNA and RNA structure, replication, transcription and RNA processing, translation, regulation of gene expression, gene expression and cell specialization, mutations, biotechnology.
- Unit 7: introduction to natural selection, natural selection, artificial selection, population genetics, Hardy-Weinberg equilibrium, evidence of evolution, common ancestry, continuing evolution, phylogeny, speciation, extinction, variations in populations, origin of life on Earth.
- Unit 8: responses to the environment, energy flow through ecosystems, population ecology, effect of density on populations, community ecology, biodiversity, disruptions to ecosystems.
For the official Course and Exam Description
The College Board publishes the full Course and Exam Description, released free-response questions, scoring guidelines and the lab manual at apcentral.collegeboard.org. Always study from the current Course and Exam Description and the College Board's own released exams, because question style and the science practices are board-specific.
Biology guides
In-depth written guides with paired practice quizzes.
Biology practice quizzes
Multiple-choice drills with worked answer explanations. Your scores stay on this device.
The AP system, explained
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