# Explain why the concentration of carbon dioxide in expired air is higher than in inspired air.

> Cambridge International IGCSE Biology (0610) — 11.1 Gas exchange in humans · Explain · 4 marks

## Mark scheme (4 marks)

1. Oxygen is used in respiration by cells / tissues
2. Carbon dioxide is produced as a waste product of respiration
3. Carbon dioxide diffuses from the blood into the alveoli
4. This carbon dioxide is then breathed out / expelled during expiration

## Key terms

- [expired air](https://www.gradenine.co.uk/glossary/expired-air)
- [inspired air](https://www.gradenine.co.uk/glossary/inspired-air)
- [carbon dioxide](https://www.gradenine.co.uk/glossary/carbon-dioxide)

## 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/explain-why-the-concentration-of-carbon-7dc63903) · Published by Druglandscape Ltd.