# Describe the changes that occur in the thorax during expiration to move air out of the lungs.

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

## Mark scheme (4 marks)

1. The diaphragm relaxes and returns to a dome shape
2. The intercostal muscles relax, causing the ribcage to move down and inwards
3. The volume of the thorax decreases
4. The pressure inside the thorax rises above atmospheric pressure, so air moves out of the lungs

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-the-changes-that-occur-in-f90a4dcb) · Published by Druglandscape Ltd.