# Explain why the rate of diffusion of oxygen into a respiring cell increases when the cell uses oxygen more rapidly.

> Pearson Edexcel International GCSE Biology (4BI1) — 2.4 Movement of substances into and out of cells · Explain · 4 marks

> Muscle cells respire rapidly during exercise, and oxygen must diffuse from the blood plasma into the muscle cells to meet the demand.

## Mark scheme (4 marks)

1. Rapid respiration uses up / removes oxygen inside the cell, lowering the concentration of oxygen inside the cell
2. This increases / steepens the concentration gradient between the blood plasma (outside) and the cell (inside)
3. Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration (down the concentration gradient)
4. A steeper concentration gradient results in a faster / greater rate of diffusion into the cell

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](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-diffusion-17c459a7) · Published by Druglandscape Ltd.