# A group of students is investigating the decomposition of leaf litter in two forest areas. In one area, the soil is well-drained and rich in oxygen. In the other area, the soil is waterlogged. Explain why the rate of decomposition differs between the two areas, and describe what happens to the carbon stored in the leaf litter in each area.

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

> Leaf litter is dead plant material that falls to the forest floor and is broken down by decomposers. The conditions in the soil affect how quickly decomposition occurs and which gases are released.

## Mark scheme (5 marks)

1. The well-drained soil has sufficient oxygen, allowing aerobic decomposition to occur.
2. Aerobic decomposition produces carbon dioxide, which is released into the atmosphere.
3. The waterlogged soil lacks oxygen, so anaerobic decomposition occurs.
4. Anaerobic decomposition produces methane (and carbon dioxide), which is released.
5. The rate of decomposition is slower in the waterlogged soil because decomposers work less efficiently without oxygen, so carbon accumulates / is stored in the leaf litter.

## Key terms

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

## 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-group-of-students-is-investigating-a72a1a43) · Published by Druglandscape Ltd.