# A farmer wants to improve the fertility of their soil by making compost from dead plant material. Explain why the rate of decomposition in the compost heap is affected by water availability, oxygen availability and temperature.

> OCR A-Level Biology B — Advancing Biology (H422) — 4.3 Energy budgets and ecosystems · Explain · 5 marks

> Decomposers such as bacteria and fungi break down dead plant material in a compost heap. The farmer notices that compost made in warm, moist and well-aerated conditions is produced much more quickly than compost made in cold, waterlogged or dry conditions.

## Mark scheme (5 marks)

1. Decomposers need water to survive / carry out enzyme-controlled reactions, so greater water availability increases decomposition rate
2. Waterlogged conditions reduce oxygen availability, leading to anaerobic decomposition which is slower than aerobic decomposition
3. Good oxygen availability allows aerobic decomposition, which is faster / more efficient than anaerobic decomposition
4. Higher temperature increases the rate of decomposition because decomposers are more active / enzyme-controlled reactions occur faster
5. Cold temperatures slow decomposition because decomposers / enzymes are less active at low temperatures

## Key terms

- [decomposition](https://www.gradenine.co.uk/glossary/decomposition)
- [compost](https://www.gradenine.co.uk/glossary/compost)

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-farmer-wants-to-improve-the-09329c87) · Published by Druglandscape Ltd.