AP Biology: how to study for the exam, unit by unit (vocabulary against mechanism, the data questions, the free-response verbs, and an eight-week plan)

AP Biology covers the chemistry of life, cells and their energetics, cell communication and the cell cycle, heredity, gene expression, natural selection and ecology, and its exam tests them through data: graphs to read, experiments to design, claims to justify with evidence. The way to study it is the released free-response questions, done under time and graded with the College Board's own scoring guidelines, with each unit learned twice, once as vocabulary and once as mechanism. Here are the units, the habits and an eight-week plan.

The AP Biology units, in our words

The College Board organizes the course into eight units. The names below are its scheme, described in our words, and the order is the one most teachers follow.

1. The chemistry of life. Water and hydrogen bonding, the four kinds of large biological molecule, and how a molecule's structure sets what it can do.
2. Cells. Organelles, the cell membrane, and how substances cross it, by diffusion, osmosis and transport proteins.
3. Cellular energetics. Enzymes, then the two pathways that move energy through life: cellular respiration and photosynthesis.
4. Cell communication and the cell cycle. How a signal outside a cell changes what happens inside it, feedback, and how a cell divides and controls its division.
5. Heredity. Meiosis, Mendel's patterns of inheritance, and the patterns that do not follow Mendel.
6. Gene expression and regulation. DNA replication, transcription and translation, how genes are switched on and off, mutation, and biotechnology.
7. Natural selection. Evolution by selection, the evidence for it, population genetics, speciation and reading phylogenetic trees.
8. Ecology. Populations, communities and ecosystems, energy flow, and how disruptions spread through them.

Natural selection is the most heavily weighted unit on the multiple-choice section in the College Board's published ranges, which surprises students who think of it as the easy chapter. It is not easy on this exam, because it is tested with numbers.

Running through every unit are the course's science practices: explaining a concept, reading and drawing models, designing and critiquing experiments, representing and analysing data, running the course's statistical tests, and arguing from evidence. Those practices are what the questions actually ask you to do. The units are only what they ask about.

The exam in one table

The figures below are the College Board's, as its AP Biology exam page states them at the time of writing. Check the page before the exam; formats change.

Section	Questions	Time	Weight
I, multiple choice	60	1 h 30 min	50 %
II, free response	6: two long, four short	1 h 30 min	50 %

The two long free-response questions carry more points than the four short ones, so budget your time toward them. The exam is hybrid digital: the multiple-choice questions are answered in the College Board's testing app, and the free-response answers are handwritten in a paper booklet. A calculator is allowed; which kinds is set by the College Board's calculator policy, so read it before you choose one. The equations and formulas reference is available throughout the exam. The score is reported from 1 to 5. Nothing from the exam is reproduced on this page; the released questions live on AP Central.

Vocabulary against mechanism: every unit is both

Every idea in AP Biology lives at two levels, and students usually learn only the first.

A term is a fact you can put on a card. What is a competitive inhibitor? A molecule that binds the enzyme's active site and blocks the substrate. That is vocabulary.

A mechanism is a process you can draw. How does a competitive inhibitor change a graph of reaction rate against substrate concentration, and why? It slows the rate at low substrate concentrations, but at high concentrations the substrate outcompetes it, so the maximum rate is the same as without the inhibitor. That is mechanism.

The multiple-choice section tests both. The data questions and the free-response section test the mechanism almost every time, usually by showing you a graph the mechanism explains. So learn each unit twice: the terms as cards, the mechanism as a diagram you can redraw.

Unit	Five terms to card	The one diagram to redraw
1 Chemistry of life	hydrogen bond, polymer, dehydration synthesis, hydrolysis, amino acid R group	a water molecule's polarity and its hydrogen bonds
2 Cells	osmosis, hypertonic, active transport, endomembrane system, surface area to volume ratio	the membrane with its transport proteins
3 Energetics	activation energy, competitive inhibitor, ATP synthase, chemiosmosis, Calvin cycle	the mitochondrion with the electron transport chain
4 Communication	ligand, second messenger, negative feedback, checkpoint, apoptosis	a signal-transduction pathway
5 Heredity	homologous chromosomes, crossing over, nondisjunction, linked genes, sex-linked	meiosis with crossing over
6 Gene expression	promoter, codon, operon, point mutation, PCR	transcription and translation
7 Natural selection	fitness, genetic drift, Hardy–Weinberg equilibrium, speciation, shared derived trait	a phylogenetic tree with a shared derived trait
8 Ecology	carrying capacity, trophic level, keystone species, net primary productivity, logistic growth	an energy pyramid

The diagrams to redraw from memory

The table's last column is the list of eight: the membrane with its transport proteins, the mitochondrion with the electron transport chain, the chloroplast with both sets of reactions, a signal-transduction pathway, meiosis with crossing over, transcription and translation, a phylogenetic tree with a shared derived trait, and an energy pyramid.

The method is short. Draw the diagram on blank paper with the book closed. Open the textbook and compare. Mark in another colour what you left out or drew wrong. Close the book and redraw it tomorrow. Roediger and Karpicke (2006) found that producing material from memory gave better recall a week later than restudying it, and a diagram drawn from nothing is that kind of production. It also shows you, in one glance, which arrow you never understood.

For the energetics and molecular units, three explainers go deeper than this page can: cellular respiration, photosynthesis and DNA to protein.

The data questions, and how they are marked

Much of the exam is data. A graph with error bars, a table of measurements, a described experiment with its variables. Three habits do most of the work.

• Name the variables before you read the data. Say which variable the experimenter changed (the independent variable) and which one was measured (the dependent variable). Then read the graph.
• Read the axes and the units aloud. Most misreadings are axis misreadings: a log scale read as linear, minutes read as seconds.
• Compute a rate as a change over a change, with units. The slope of a line is a rate, and its unit is the y unit over the x unit.

The course also uses two procedures with numbers, and both are learned the way maths is learned: by worked example, then cold. The first is the chi-square test, which asks whether observed counts differ from expected counts by more than chance. The second is Hardy–Weinberg, which predicts allele and genotype frequencies in a population that is not evolving. Sweller and Cooper (1985) found that students who studied worked examples before solving problems learned a procedure faster and with fewer errors, and both procedures reward exactly that. For the genetics crosses that feed chi-square questions, Punnett squares has the method.

The free-response verbs

The single habit that moves free-response scores is reading the verb. Each question part begins with a verb, and the verb says what earns the point.

• Identify asks for a name or a value, no explanation.
• Describe asks what happens, in a sentence or two.
• Explain asks how or why, which means a mechanism.
• Predict asks what will happen and usually wants the reason with it.
• Justify asks for evidence or a reason tied to a mechanism, not a restatement of your claim.

So underline the verb, answer that verb first in one sentence, then add the evidence. A part that asks you to justify and gets back your prediction in other words earns nothing, however long it is.

Practise on the released free-response questions on AP Central, under the real time, then grade your own answer against the published scoring guideline for that question. The guideline shows you, point by point, what a reader gave and what you left out. That material is the College Board's and is not reproduced here. The examples below are ours.

Worked example: two questions of ours, done the FRQ way

These are our own problems, written in the free-response style. They are not AP items.

Hardy–Weinberg

In a population at Hardy–Weinberg equilibrium, 9 % of individuals show a recessive trait. Predict the frequency of carriers, and the frequency of the dominant phenotype.

• Recessive phenotype frequency is q², so q² = 0.09.
• Take the square root: q = 0.3.
• The two allele frequencies add to 1, so p = 1 − 0.3 = 0.7.
• Carriers are heterozygotes, frequency 2pq = 2 × 0.7 × 0.3 = 0.42.
• The dominant phenotype is everyone who is not recessive: p² + 2pq = 0.49 + 0.42 = 0.91. Check: 1 − 0.09 = 0.91.

The carrier frequency is 0.42 and the dominant phenotype frequency is 0.91. The common wrong line is q = 0.09: the 9 % is q², the frequency of the genotype, not of the allele. Taking q = 0.09 gives a carrier frequency near 0.16, and every number after it is wrong.

A rate from data

A student measures the oxygen consumed by germinating seeds in a closed chamber. The reading is 2.4 mL at 0 minutes and 8.4 mL at 10 minutes. Calculate the rate of oxygen consumption, then predict the effect of a lower temperature.

• The independent variable is time; the dependent variable is the volume of oxygen consumed.
• Change in volume: 8.4 − 2.4 = 6.0 mL.
• Change in time: 10 − 0 = 10 min.
• Rate: 6.0 mL ÷ 10 min = 0.6 mL/min.

The rate is 0.6 mL of oxygen per minute. For the prediction: at a lower temperature the rate of oxygen consumption decreases, because the enzymes of cellular respiration catalyse reactions more slowly when molecules collide less often and with less energy. The answer to "predict" is the first clause. The point for the reason comes from naming the mechanism, enzyme activity in respiration, not from "because it is colder".

Where SBI4U overlaps, for Canadian readers

Ontario's Grade 12 biology course covers much of AP Biology's chemistry, energetics and molecular genetics, and less of its evolution and cell biology. The table reads SBI4U's map against the AP units. "Overlaps" means the ideas are taught; it does not mean one course is credit for the other.

AP unit	On SBI4U's map	New for an SBI4U student
1 Chemistry of life	Yes: water, macromolecules, protein structure	Little
2 Cells	Membranes and transport yes	Organelles and surface area to volume
3 Energetics	Yes: enzymes, glycolysis to the electron transport chain, both stages of photosynthesis	Little
4 Communication and cell cycle	Hormonal control and feedback yes	Signal transduction in depth, the cell cycle
5 Heredity	Patterns of inheritance yes	Meiosis, linkage, chi-square
6 Gene expression	Yes: replication, transcription, translation, control, biotechnology	Little
7 Natural selection	No	The whole unit, with Hardy–Weinberg and phylogeny
8 Ecology	Population growth and community interactions yes	Energy flow and ecosystems

So the new work for an SBI4U student is natural selection as a quantitative unit, phylogeny, meiosis and the cell cycle, cell signalling, and the free-response habit itself.

How to study for AP Biology: the method

1. Terms as cards, each with your own example. A card that says "keystone species" on the front and "a species whose removal changes the whole community" on the back is half a card. Add your own example on the back. How to write a card that forces recall has the shape.
2. Mechanisms as diagrams redrawn from the list of eight, each one twice: once when you learn it, once the next day.
3. Data by worked example, then cold. Chi-square, Hardy–Weinberg and rate calculations: read one worked example, redo it with the book closed, then do a sibling with new numbers.
4. Mixed sets from week 2. Rohrer and Taylor (2007) found that practice shuffled across problem types felt harder and tested better than practice blocked by type. The exam is shuffled. Why mixing beats blocking has the research.
5. One released free-response set a week, under time, self-scored against the guideline.
6. The error log by skill. Log every miss with the skill it tested, where a skill is a verb or a mechanism ("justify with a mechanism", "read a log axis"), not a unit. The practice-test method has the log's columns.

The eight-week plan (AP bio review, week by week)

Week	Cards and diagrams	Data drill	Free response
1	Diagnostic: one released full exam under time, then the error log by skill; units 1–2 cards	Rates from graphs	The diagnostic's free-response section, self-scored
2	Units 3–4 cards; respiration and signal-transduction diagrams	Mixed sets across units 1–4	One short-question set
3	Units 5–6 cards; meiosis and transcription diagrams	Chi-square by worked example, then cold	One released set under time
4	Units 7–8 cards; tree and pyramid diagrams	Hardy–Weinberg by worked example, then cold	One released set under time
5	All eight diagrams from memory; every unit's cards	Mixed sets across all units	One long question, timed
6	A second released full exam under time; the log's top three skills	The top three skills, mixed with everything	The second exam's section, self-scored
7	Cards only, every unit	One mixed set a day	Two sets under time, verbs underlined first
8	The compressed final week, light on the last two days	One short set a day	None after day 3

Week 8 is the seven-day plan in chapter 9 of the free playbook: the log's last skills early in the week, one timed section two days out, a light final day and a full night's sleep before the exam.

AP Biology, on one screen

• The units: chemistry of life, cells, energetics, communication and the cell cycle, heredity, gene expression, natural selection, ecology.
• The exam: 60 multiple-choice questions in 90 minutes and six free-response questions in 90 minutes, half the score each, a calculator allowed.
• Vocabulary against mechanism: every unit as cards and as a diagram.
• The eight diagrams: membrane, mitochondrion, chloroplast, signalling pathway, meiosis, transcription and translation, phylogenetic tree, energy pyramid.
• The free-response verbs: underline the verb, answer it first, then the evidence.
• The plan: a diagnostic in week 1, two units a week, a second full exam in week 6, a light final week.