# Describe how nitrogen from the atmosphere is made available to plants, and explain why plants need nitrogen.

> AQA A-Level Biology (7402) — 3.5.4 Nutrient Cycles · Describe and Explain · 5 marks

## Mark scheme (5 marks)

1. Nitrogen gas in the atmosphere is fixed / converted into nitrates (or ammonia/ammonium compounds) by nitrogen-fixing bacteria
2. Nitrogen-fixing bacteria live in the soil or in root nodules of leguminous plants
3. Nitrates are absorbed by plant roots (from the soil)
4. Plants use nitrogen to make / synthesise proteins
5. Plants also use nitrogen to make DNA / genetic material / nucleic acids

## Related

- [Revision notes for AQA A-Level Biology (7402)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-nitrogen-from-the-atmosphere-dbd5d0e6) · Published by Druglandscape Ltd.