# Describe the role of microorganisms in the nitrogen cycle, including the names of the specific types of bacteria involved.

> Cambridge International IGCSE Biology (0610) — 19.3 Nutrient cycles · Describe · 4 marks

## Mark scheme (4 marks)

1. Decomposers break down protein in dead organisms / waste to produce ammonium ions
2. Nitrifying bacteria convert ammonium ions into nitrates (accept: ammonium ions → nitrites → nitrates)
3. Nitrogen-fixing bacteria convert atmospheric nitrogen gas into ammonia / ammonium ions / nitrates (accept: found in soil or root nodules of legumes)
4. Denitrifying bacteria convert nitrates back into nitrogen gas, returning it to the atmosphere

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-the-role-of-microorganisms-in-abeac1eb) · Published by Druglandscape Ltd.