Free topic guides
A-level Biology revision, written the way it is marked
Every guide answers the question first, then gives you the order to write the answer in, the exact phrases that earn marks, and the errors that lose them. Written against the CCEA GCE Biology specification and valid for AQA A-level Biology too. CCEA and AQA publish the definitive specifications; BioCCEA is an independent study tool.
AS topics
- The cardiac cycle: stages, pressures and valve timingsThe three stages of the cardiac cycle, how pressure changes open and close each valve, and how to read the pressure–volume graph that turns up in almost every heart question.
- Transpiration and the cohesion–tension theoryHow water moves from root to leaf, why cohesion–tension rather than suction, the four factors that change transpiration rate, and how to answer potometer data questions.
- Water potential: the right way to explain osmosisWhat water potential means, why it is always zero or negative, how solute and pressure potential combine, and how to describe osmosis in plant and animal cells for full marks.
- The immune response: cells, antibodies and immunological memoryPhagocytosis, the cell-mediated and humoral responses, antibody structure, and why the secondary response is faster — written for A-level extended-response questions.
A2 topics
- The light-dependent reaction, explained for A-level BiologyWhat happens in the light-dependent reaction, where each product goes, and the exact wording that earns marks on CCEA A2 1 and AQA photosynthesis questions.
- Dihybrid inheritance: how to set out the cross and get the ratio rightHow to lay out a dihybrid cross, where the 9:3:3:1 ratio comes from, how to handle sex linkage and linked genes, and the marks examiners award line by line.
- The Krebs cycle: what to remember and what to leave outThe Krebs cycle for A-level Biology: where it happens, the carbon count, how much reduced NAD and FAD each turn makes, and how it feeds oxidative phosphorylation.
- Action potentials: resting potential, depolarisation and the refractory periodHow an action potential is generated and propagated, why it is all-or-nothing, what the refractory period is for, and the sequence examiners expect in a description.
- Muscle contraction: the sliding filament theory step by stepSarcomere structure, the sliding filament theory, the role of calcium, tropomyosin and ATP, and which bands change length when a muscle contracts.
- The chi-squared test in A-level Biology, worked throughWhen to use chi-squared, how to calculate it, how to work out degrees of freedom and read the critical value at p = 0.05, and how to word the conclusion for full marks.
- Standard deviation and error bars in A-level BiologyWhat standard deviation tells you about biological data, how to calculate it, the difference from standard error, and how to interpret overlapping error bars in exam answers.
- The loop of Henle and the counter-current multiplierHow the loop of Henle concentrates urine: the descending and ascending limbs, the counter-current multiplier, the role of ADH, and the wording that scores in exams.
- Natural selection: the five-step explanation examiners wantThe exact sequence for explaining natural selection, the three types of selection, how speciation follows, and the phrases that lose marks in evolution questions.
Practise these topics properly
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