The exam format
The even split between sections has a direct planning consequence: practising only multiple-choice questions caps your preparation at half the exam. The free-response section is scored on written reasoning and experimental design, and the only realistic practice for it is released free-response questions with their scoring guidelines.
| Item | Detail |
|---|---|
| Total length | Approximately 3 hours |
| Section I | 60 multiple-choice questions, 50% of the score |
| Section II | 6 free-response questions, 50% of the score |
| Free-response breakdown | 2 long questions and 4 short questions |
| Delivery | Hybrid - multiple choice digitally, free responses hand-written |
| Content | Eight units, from chemistry of life through ecology |
| Score scale | 1 to 5 |
Practice: cells, energetics and communication
A plant cell is placed in a solution and its volume decreases. What can be concluded about the solution?
It is hypertonic relative to the cell, so water moved out by osmosis down its water potential gradient. Two precision points the exam cares about: tonicity is always a comparison, so hypertonic on its own is meaningless without saying relative to what; and in a plant cell continued water loss causes plasmolysis, where the membrane pulls away from the cell wall, which is why plant and animal cells behave differently in the same solution.
Mitochondria are treated with a chemical that inhibits ATP synthase. Researchers observe that a proton gradient still forms across the inner membrane, but ATP production stops. What does this support?
That the electron transport chain establishes the proton gradient independently of ATP synthase, and that ATP synthase is the component coupling that gradient to ATP synthesis. This is a characteristic AP question: it does not ask you to describe chemiosmosis, it gives you an experimental result and asks what it demonstrates. Contrast it with an uncoupler, which would let protons leak across the membrane so that no gradient forms and energy is released as heat instead.
A mutation prevents a G protein from hydrolysing GTP. What is the most likely effect on the signalling pathway?
The pathway remains active continuously, because GTP hydrolysis is the off switch. A G protein is active when bound to GTP and inactive when bound to GDP, so a protein that cannot hydrolyse stays switched on and keeps propagating the signal even without a ligand. Constitutive activation of this kind underlies several cancers, and the exam frequently connects signalling mechanisms to that consequence.
Practice: heredity, gene expression and evolution
Two parents are both heterozygous for an autosomal recessive disorder. What is the probability that a child is a carrier?
One half. The cross gives one quarter homozygous dominant, one half heterozygous and one quarter homozygous recessive. Carriers are the heterozygotes, so one half. The frequent error is answering one quarter, which is the probability of being affected. Read whether the question asks about affected, carrier, or unaffected - unaffected would be three quarters, of which two thirds are carriers.
In a population at Hardy-Weinberg equilibrium, the frequency of the homozygous recessive phenotype is 0.09. What proportion of the population is heterozygous?
0.42. The homozygous recessive frequency is q squared, so q is 0.3 and p is 0.7. Heterozygotes are 2pq, which is 2 times 0.7 times 0.3, giving 0.42. Work in that order every time - q squared, then q, then p, then 2pq - because the equations are given but the sequence is not, and starting anywhere else wastes time.
After a prolonged drought, the distribution of beak depth in a finch population shifts toward larger beaks with reduced variation at the smaller end. Which mode of selection is this?
Directional selection, because one extreme of the distribution is favoured and the mean shifts toward it. Compare with stabilising selection, which favours intermediate values and narrows the distribution around the existing mean, and disruptive selection, which favours both extremes and can produce a bimodal distribution. Questions describe the shape change rather than naming it, so learn to read the distribution.
Practice: experimental design
Experimental reasoning is not confined to the free-response section. It appears in the multiple choice too, and it is the single most transferable thing to prepare, because it applies to any unfamiliar scenario the exam invents.
A researcher tests whether light intensity affects the rate of photosynthesis in an aquatic plant by counting oxygen bubbles produced. What is the dependent variable?
The rate of oxygen production, measured as bubbles per unit time - the thing being measured in response to the manipulated variable. The independent variable is light intensity. Controlled variables would include temperature, carbon dioxide availability, the species and mass of plant, and the duration of each trial. The exam expects you to name controlled variables specifically rather than to say everything else was kept the same.
In the same experiment, why would a trial run in complete darkness be included?
As a control establishing the baseline rate of bubble production when the independent variable is absent, so any oxygen detected can be attributed to something other than photosynthesis. A control is not simply an extra trial - it isolates the effect being tested by removing the variable while holding everything else constant. Being able to state what a control rules out is a reliable source of marks.
Practice this now
How to prepare for a subject this large
- ✓Study the eight units as connected mechanisms rather than as separate chapters. The exam routinely spans units - a question about cell signalling can lead into gene expression and then into cancer.
- ✓Practise with released free-response questions and their scoring guidelines. The guidelines tell you exactly what earns a point, and the answer is almost always more specific than students expect.
- ✓Learn to read graphs and data tables fast. Data interpretation appears throughout both sections and is the skill most transferable to unfamiliar questions.
- ✓Write experimental-design answers in a fixed structure: independent variable, dependent variable, controlled variables, control group, prediction. Having a template stops you omitting a component under time pressure.
- ✓Use active recall on the vocabulary rather than rereading. You need the terms fluently enough to reason with them, and rereading does not produce fluency.
- ✓Practise the hybrid format itself so the mechanics are familiar - digital multiple choice followed by hand-written responses is a switch worth rehearsing.