# Explain why the rate of photosynthesis in a plant decreases when the concentration of carbon dioxide in the air falls below a certain level.

> AQA GCSE Biology (8461) — 4.4.1 Photosynthesis · Explain · 4 marks

## Mark scheme (4 marks)

1. Carbon dioxide is a reactant in / needed for photosynthesis
2. Carbon dioxide acts as a limiting factor (when in low concentration)
3. There is not enough carbon dioxide to maintain the current rate of reaction / the plant cannot photosynthesise as fast
4. Increasing carbon dioxide concentration (above this level) would increase the rate of photosynthesis / another factor then becomes limiting

## Key terms

- [photosynthesis](https://www.gradenine.co.uk/glossary/photosynthesis)
- [carbon dioxide](https://www.gradenine.co.uk/glossary/carbon-dioxide)

## Related

- [Revision notes for AQA GCSE Biology (8461)](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/explain-why-the-rate-of-photosynthesis-e5fe6648) · Published by Druglandscape Ltd.