AP Bio study guide: A revision compendium organized by unit

AP (Advanced Placement) Biology covers eight CED units, four big ideas that cut across all of them, and a required lab component (many classes use College Board's 13 investigations). That's a lot of surface area, and a study guide that just lists topics doesn't help you decide what to revise first when you've got six weeks and a shelf of textbooks.

This guide is organized the way an actual revision plan should be: the four big ideas first (because they connect every unit), then the eight units in weighted order (highest exam weight first), then the topics within each unit that appear most on recent released exams. If you'd rather revise from short video lessons with practice questions attached, Cognito's AP Biology notes cover every CED subtopic.

Every AP Bio topic sits under one or more of the CED's four big ideas. If your revision only tags topics (photosynthesis, mitosis, natural selection), you'll miss the through-lines that let you write a stronger FRQ.

Evolution: Common ancestry, natural selection, phylogeny, speciation. Comes up in Unit 7, but also anywhere the exam asks 'why is this trait conserved' or 'what selective pressure could explain this'.

Energetics: How energy moves through and between organisms. Threads through cellular respiration, photosynthesis, thermodynamics of enzymes and ecosystem energy flow.

Information storage and transmission: DNA structure, replication, transcription, translation, gene regulation, inheritance. Central to Units 5 and 6 but also to Unit 4 (cell communication and signaling).

Systems interactions: Feedback loops, homeostasis, ecosystem dynamics. Shows up most in Units 4 and 8.

Before reading any unit, ask yourself which big idea it slots into. That framing helps you move from 'the mitochondria makes ATP' to 'the free energy released by glucose oxidation is captured in ATP for cellular work'.

Two units (natural selection and cellular energetics) together account for a quarter to a third of exam weight. If your revision time is limited, they earn the biggest slice. Hardy-Weinberg calculations and photosynthesis or respiration data questions are recurring features of released papers.

The course requires lab work for at least 25 percent of instructional time, with a minimum of two labs per big idea; many teachers use the 13 investigations in College Board's AP Biology Investigative Labs manual, and FRQs often draw on lab-style experimental setups. You don't need to memorize the wet-lab steps, but you should be able to describe the independent variable, dependent variable, control, hypothesis and expected result for each. The ones most commonly tested are the diffusion and osmosis lab (Investigation 4), the enzyme catalysis lab (Investigation 13), the photosynthesis lab (Investigation 5) and the population genetics lab (Investigation 2, Hardy-Weinberg simulation).

A quick drill: for each lab, write one sentence describing what you'd graph on the x-axis and what you'd graph on the y-axis. If you can do that from memory for all 13, you'll handle the lab-based FRQ.