A fallen oak tree in a forest is gradually broken down over several years. Explain the conditions that would cause the tree to decompose most rapidly.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Decomposers such as bacteria and fungi are responsible for breaking down dead organic material, including fallen trees, in forest ecosystems. The rate at which this decomposition occurs depends on several environmental conditions.
Model answer (5 marks)
High temperature increases the rate of decomposition because enzymes in bacteria and fungi work faster and have more kinetic energy at higher temperatures (up to their optimum). Moist or high‑moisture conditions also increase the rate because water is required for enzyme activity and for the transport of nutrients. Presence of oxygen, i.e. aerobic conditions, increases the rate because decomposers need to respire to release energy for growth and reproduction and to carry out metabolic processes.
Examiner tips
- Use the exact terms: high temperature, moist conditions, presence of oxygen, aerobic conditions.
- Explain the underlying reason for each condition – enzyme activity and respiration.
- Keep each point concise – one sentence per point to match the 5 marks.
Common mistakes
- Confusing anaerobic with aerobic conditions – remember decomposers need oxygen.
- Omitting the reason why temperature or moisture matters – just stating the condition is insufficient.
- Using vague terms like ‘fast’ instead of ‘enzyme activity’ or ‘respiration’.”
Mark scheme (5 marks)
- High temperature increases the rate of decomposition
- Because enzymes in decomposers work faster / have more kinetic energy at higher temperatures (up to the optimum)
- Moist / high moisture conditions increase the rate of decomposition
- Presence of oxygen / aerobic conditions increase the rate of decomposition
- Because decomposers need to respire to release energy for growth and reproduction / metabolic processes
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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