The AP (Advanced Placement) Biology Course and Exam Description, or CED, is the 200-plus-page document CollegeBoard publishes to tell teachers exactly what's tested and how. It has learning objectives, essential knowledge statements, science practices, exam format details and sample questions. It's the single source of truth for what shows up in May, and it's easy to get lost in.
This guide is the working summary. Every unit gets its exam weight, its enduring understandings and the science practices it emphasizes, plus a note on the content students most commonly under-prepare for. If you want the underlying content taught in full instead of just summarized, Cognito's AP Biology notes match the CED unit structure and skill practices.
How the CED is structured
The CED breaks the course into eight units. Every unit maps to one or more of the four big ideas (evolution, energetics, information storage and transmission, systems interactions) and touches several of the six science practices. The six science practices are: concept explanation, visual representations, questions and methods, representing and describing data, statistical tests and data analysis, and argumentation.
An important point that gets missed: each FRQ part is written to assess a specific science practice. When a question asks you to 'justify' a claim, that's Practice 6 (argumentation), and the rubric point goes to the reasoning that supports the claim, not just to a correct conclusion. Reading FRQ stems for the practice being tested is one of the most useful upgrades a lot of students can make.
Unit 1: Chemistry of life (8 to 11 percent)
Key ideas: The properties of water arise from its structure; carbon-based molecules are the building blocks of life; nucleic acids store and transmit information; the primary structure of a protein determines its final shape.
Most commonly tested: how hydrogen bonds shape DNA and water; the four levels of protein structure and what disrupts each; monomer-to-polymer relationships across the four macromolecule families.
Where students under-prepare: functional groups on organic molecules (hydroxyl, carbonyl, carboxyl, amino, phosphate, sulfhydryl). The CED doesn't list them by name, but recognizing them makes diagram-based questions much easier. If you can't look at a molecular diagram and name the groups, an FRQ that asks 'which of these could form a hydrogen bond' becomes much harder than it needs to be.
Unit 2: Cell structure and function (10 to 13 percent)
Key ideas: Cellular structure supports cellular function; membranes regulate the movement of materials; cellular compartmentalization allows for specialized functions.
Most commonly tested: SA:V ratio and its consequences for cell size and diffusion; membrane transport (passive, active, primary and secondary); water potential calculations for plant cells.
Where students under-prepare: the endomembrane system as an integrated whole. The exam often asks students to trace a protein from ribosome to secretion (ER, Golgi, vesicle, plasma membrane), and the specific role of each organelle in that pipeline is easy to muddle if you learned them as isolated cards.
Unit 3: Cellular energetics (12 to 16 percent)
Key ideas: Enzymes catalyze biological reactions; cellular respiration and photosynthesis extract and store energy in ATP; the free energy available for work is determined by conditions in the cell.
Most commonly tested: how the chemiosmotic gradient drives ATP synthesis; effect of temperature and pH on enzyme rate; the location and net yield of glycolysis, Krebs cycle and electron transport chain; the Calvin cycle's role in fixing carbon.
Where students under-prepare: the CED explicitly asks for connections between photosynthesis and cellular respiration (they use complementary electron carriers, opposite carbon flows and the same chemiosmotic principle). Learning them as separate topics leaves you weaker on the FRQs that ask you to compare them.
Unit 4: Cell communication and cell cycle (10 to 15 percent)
Key ideas: Cells communicate by generating, transmitting, receiving and responding to chemical signals; feedback loops maintain homeostasis; the cell cycle is regulated by checkpoints.
Most commonly tested: negative feedback loops in blood glucose regulation and thermoregulation; signal transduction (receptor, secondary messenger, cellular response); what happens at each cell cycle checkpoint and how cancer relates to checkpoint failure.
Where students under-prepare: positive feedback loops. Feedback is a recurring FRQ theme, and the classic positive feedback examples (childbirth contractions, blood clotting, fruit ripening) are often less well drilled than the negative ones.
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Unit 5: Heredity (8 to 11 percent)
Key ideas: Meiosis produces genetic diversity; inheritance follows patterns that can be predicted; not all inheritance is Mendelian.
Most commonly tested: dihybrid cross probability and independent assortment; pedigree analysis to determine mode of inheritance; sex-linked inheritance and its consequences for expected phenotype ratios.
Where students under-prepare: linkage. The CED expects students to know that genes on the same chromosome tend to be inherited together and to recognize when observed data deviate from expected independent-assortment ratios.
Unit 6: Gene expression and regulation (12 to 16 percent)
Key ideas: DNA and RNA carry genetic information; the phenotype is derived from expression of the genotype; gene expression is regulated at multiple levels; genetic engineering has consequences for society.
Most commonly tested: consequences of a specific mutation for protein function (silent, missense, nonsense, frameshift); the lac and trp operons under various conditions; the difference between eukaryotic and prokaryotic transcription and translation.
Where students under-prepare: epigenetics. Chromatin structure, DNA methylation and histone modification appear in recent FRQs, and they're rarely taught with the same time investment as replication and transcription.
Unit 7: Natural selection (13 to 20 percent)
Key ideas: Natural selection acts on phenotypic variation; evolution is supported by evidence from multiple lines; populations evolve when specific conditions are or are not met; species arise through reproductive isolation.
Most commonly tested: Hardy-Weinberg allele and genotype frequency calculations; phylogenetic tree interpretation; conditions required for a population to be in equilibrium; allopatric versus sympatric speciation.
Where students under-prepare: the exact five conditions of Hardy-Weinberg equilibrium (no mutation, no migration, no natural selection, random mating, large population). Getting Hardy-Weinberg right on the math is one thing; explaining why a real population fails to meet the equilibrium conditions is a separate rubric point that's easier to lose.
Unit 8: Ecology (10 to 15 percent)
Key ideas: Ecosystems have structure and dynamics; energy flows through ecosystems and matter cycles; interactions between populations shape communities; disturbances change ecosystem dynamics.
Most commonly tested: exponential versus logistic growth curves and their equations; Simpson's Diversity Index; food web trophic levels and the 10 percent energy transfer rule; the carbon and nitrogen cycles.
Where students under-prepare: how a described disturbance changes both community composition and biogeochemical cycling. Recent FRQs increasingly ask ecosystem-scale reasoning instead of isolated population math.
The CED's science practices are as testable as its content. Read every FRQ prompt for the verb: 'describe' wants observation; 'explain' wants mechanism; 'justify' wants an evidence-based claim; 'predict' wants a specific direction of change. The wrong verb answered is a lost rubric point.
Study AP Biology with Cognito
Content and practice questions organized by CED unit and skill practice, so revision targets what CollegeBoard actually tests rather than a generic textbook order.
