# A student investigates the effect of light intensity on the rate of photosynthesis in a pondweed. As light intensity increases, the rate of photosynthesis increases, but above a certain light intensity the rate no longer increases. Explain why the rate of photosynthesis increases as light intensity increases, and explain why the rate stops increasing at high light intensities.

> Pearson Edexcel A-Level Biology A (9BI0) — 3.1 Photosynthesis · Explain · 5 marks

> Photosynthesis is the process by which plants use light energy to produce glucose from carbon dioxide and water. The word equation for photosynthesis is: carbon dioxide + water → glucose + oxygen.

## Mark scheme (5 marks)

1. Light provides the energy needed for photosynthesis to occur
2. As light intensity increases, more light energy is available, so the rate of photosynthesis increases
3. At high light intensities another factor becomes limiting
4. The limiting factor is carbon dioxide concentration OR temperature
5. Even if light intensity is increased further, the rate cannot increase because the limiting factor restricts the process

## Key terms

- [photosynthesis](https://www.gradenine.co.uk/glossary/photosynthesis)
- [light intensity](https://www.gradenine.co.uk/glossary/light-intensity)

## 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/a-student-investigates-the-effect-of-41c07d12) · Published by Druglandscape Ltd.