# A scientist investigates how the concentration of carbon dioxide in the air affects the rate of photosynthesis in a water plant. At very low carbon dioxide concentrations, the rate of photosynthesis remains low even when light intensity is increased. Explain why carbon dioxide concentration acts as a limiting factor in this situation, and describe what happens inside the chloroplasts during photosynthesis.

> OCR GCSE Biology A: Gateway Science (J247) — B1.4 Photosynthesis · Explain · 4 marks

> A water plant is kept in a sealed container with a very low concentration of carbon dioxide. Despite being placed under a bright lamp, the plant produces very little oxygen.

## Mark scheme (4 marks)

1. Carbon dioxide is a reactant needed for photosynthesis to occur
2. When carbon dioxide is in short supply it limits the rate of photosynthesis regardless of other factors
3. Photosynthesis takes place in the chloroplasts, which contain chlorophyll
4. Carbon dioxide and water are converted into glucose and oxygen using light energy

## Key terms

- [limiting factor](https://www.gradenine.co.uk/glossary/limiting-factor)
- [photosynthesis](https://www.gradenine.co.uk/glossary/photosynthesis)
- [chloroplasts](https://www.gradenine.co.uk/glossary/chloroplasts)

## Related

- [Revision notes for OCR GCSE Biology A: Gateway Science (J247)](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-scientist-investigates-how-the-concentration-f002a10e) · Published by Druglandscape Ltd.