# Oxygen produced during photosynthesis must diffuse from the mesophyll cells of a leaf to the air outside. Explain how the concentration gradient and the diffusion distance each affect the rate at which oxygen diffuses out of the leaf.

> Cambridge International IGCSE Biology (0610) — 3.1 Diffusion · Explain · 4 marks

## Mark scheme (4 marks)

1. A greater concentration gradient increases the rate of diffusion of oxygen out of the leaf
2. Because more oxygen molecules move from the high concentration area to the low concentration area per unit time / there is a greater net movement of particles down the gradient
3. A smaller diffusion distance increases the rate of diffusion of oxygen
4. Because oxygen molecules need to travel a shorter distance / take less time to reach the outside air

## Key terms

- [diffusion](https://www.gradenine.co.uk/glossary/diffusion)
- [concentration gradient](https://www.gradenine.co.uk/glossary/concentration-gradient)
- [diffusion distance](https://www.gradenine.co.uk/glossary/diffusion-distance)

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](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/oxygen-produced-during-photosynthesis-must-diffuse-65e2d9f3) · Published by Druglandscape Ltd.