# Explain how oxygen moves from the air sacs (alveoli) in the lungs into the blood during breathing.

> WJEC GCSE Biology (Wales) — 1.1.2 Movement of substances · Explain · 4 marks

> Oxygen is needed by body cells for respiration. It must cross from the air sacs in the lungs into the bloodstream before it can reach those cells.

## Mark scheme (4 marks)

1. The process by which oxygen moves is diffusion
2. Oxygen moves from a high concentration (in the air sacs) to a low concentration (in the blood)
3. There is a concentration gradient between the air sacs and the blood
4. No energy is required / it is a passive process

## Related

- [Revision notes for WJEC GCSE Biology (Wales)](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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