AQA AS Biology Past Papers & Mark Schemes

Biology at AS level punishes vague language. The mark scheme distinguishes between similar-sounding words that carry different biological meanings: 'move' is not the same as 'diffuse'; 'break down' is not 'hydrolyse'; 'copy' is not 'replicate'. When describing a biological process, use the precise scientific term. In enzyme questions, say 'the substrate binds to the active site, forming an enzyme-substrate complex' — not 'the enzyme breaks down the substrate'. Active and passive voice matter too: proteins are 'synthesised at ribosomes', not 'made by the cell'. Enzyme kinetics questions are common and require both graphical interpretation and mechanistic understanding. Know the shapes of the rate curves for competitive and non-competitive inhibition, and be able to explain them in terms of molecular interactions. Competitive inhibitors have a similar shape to the substrate and compete for the active site — increasing substrate concentration can overcome this inhibition. Non-competitive inhibitors bind to an allosteric site, changing the shape of the active site — increasing substrate concentration does not overcome this. The immune response is a topic where students frequently lose marks through imprecise sequencing. Learn the specific order: antigen presentation by macrophages → clonal selection of specific T-helper and B-cells → clonal expansion → B-cells differentiate into plasma cells (which secrete antibodies) and memory cells → T-killer cells destroy infected cells by lysis. Each step has specific cell types and specific molecular interactions — mixing these up or using generic terms loses marks. Extended response questions (6 marks) in AS Biology require continuous prose, not bullet points. Plan your answer before writing: identify three or four key points, arrange them in logical order, and write coherent paragraphs. The mark scheme typically allocates marks for both scientific content and the quality of written communication — disorganised answers with correct biology can still lose marks for poor communication.