# A student investigates the rate of decomposition of dead leaves in two different compost heaps. One compost heap is kept moist and regularly turned to allow air in. The other compost heap is waterlogged and never turned. Explain why the rate of decomposition differs between the two compost heaps.

> OCR A-Level Biology B — Advancing Biology (H422) — 4.2 Respiration · Explain · 5 marks

> Decomposition is the process of breaking down dead material into simple organic matter. Decomposers, such as microorganisms, carry out this process. The rate of decomposition is influenced by water availability, oxygen availability and temperature.

## Mark scheme (5 marks)

1. The moist, turned compost heap has sufficient oxygen available (for aerobic decomposition)
2. Decomposers / microorganisms respire aerobically in the moist, turned heap, releasing more energy to break down dead material faster
3. The waterlogged compost heap has little or no oxygen available (anaerobic conditions)
4. Anaerobic decomposition is slower / less efficient than aerobic decomposition
5. Therefore the moist, turned compost heap decomposes faster / produces compost more quickly than the waterlogged heap

## 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-student-investigates-the-rate-of-ab8a66d3) · Published by Druglandscape Ltd.