# Decomposers play an essential role in the recycling of nutrients in ecosystems. Explain how decomposers break down dead organic matter and describe three environmental conditions that affect the rate of decomposition.

> Pearson Edexcel A-Level Biology A (9BI0) — 5.5 Decomposition and decay · Explain · 5 marks

> In a woodland ecosystem, fallen leaves and dead organisms accumulate on the forest floor. Over time, these materials are broken down and their nutrients are returned to the soil.

## Mark scheme (5 marks)

1. Decomposers (bacteria and fungi) secrete enzymes onto dead organic matter / digest it extracellularly
2. Soluble products are absorbed by the decomposers / nutrients are released into the soil
3. Temperature affects rate of decomposition — higher temperatures (up to an optimum) increase the rate because enzyme activity increases
4. Moisture / water availability affects decomposition — moist conditions increase the rate as decomposers need water for metabolic reactions / enzyme activity
5. Oxygen / aerobic conditions affect decomposition — more oxygen increases the rate as aerobic decomposers respire aerobically and are more active

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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/decomposers-play-an-essential-role-in-cd215ad1) · Published by Druglandscape Ltd.