Exam Focus

Decomposition is examined regularly on AQA Paper 2, often in the context of the Required Practical (RPA6/RPA10 — investigating factors affecting decomposition rate). Questions frequently link decomposition to the carbon cycle and nutrient recycling. Key patterns:

• Factor explanation questions (2–3 marks): "Explain how temperature affects the rate of decomposition" — always link to enzyme activity, state the optimum, and explain denaturation at high temperatures.
• Required Practical questions (3–4 marks): "Describe how you would investigate the effect of moisture on the rate of decomposition" — state the independent variable, dependent variable, control variables, and how you would measure the rate.
• Comparison questions (2–3 marks): "Explain why decomposition is slower in peat bogs than in garden soil" — link to anaerobic conditions, low pH, and reduced enzyme activity.
• Biogas questions (2–3 marks): State conditions needed for biogas production and explain why anaerobic conditions are necessary.

Common mark-losing errors: Saying "bacteria eat dead material" rather than secreting enzymes externally; saying high temperature always speeds decomposition (ignoring denaturation); forgetting fungi as major decomposers; confusing decomposers with detritivores.

Edexcel 1BI0 Paper 2 (T9 — Ecosystems and Material Cycles): Edexcel decomposition questions often appear as data interpretation items — a graph or table showing decomposition rate under different temperature, moisture, or pH conditions, with questions asking you to describe the pattern and explain it using enzyme theory. Required Practical-style questions may ask you to evaluate an experimental design for investigating decay rate and suggest improvements. Biogas generator scenarios test your knowledge of anaerobic decomposition and the conditions needed for methane production. Edexcel mark schemes use "Accept…" and "Allow…" for equivalent enzyme-based explanations of decomposition rate changes.