Describe the changes that occur in the thorax during inspiration to move air into the lungs.

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

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. The external intercostal muscles contract, raising the ribcage up and out.
2. The diaphragm contracts and flattens.
3. The volume of the thorax increases.
4. Thoracic pressure falls below atmospheric pressure, so air moves into the lungs.

Examiner tips

Use the exact wording from the mark scheme; list points in order.
Include all four points to earn full marks.
Use concise, factual sentences.
Show the cause–effect relationship (muscle action → volume change → pressure drop).

Common mistakes

Omitting the diaphragm action or the pressure change.
Using vague terms like ‘breathing in’ instead of specific muscle actions.
Listing the points out of order or missing one of the four key points.

Mark scheme (4 marks)

The external intercostal muscles contract, raising the ribcage up and out
The diaphragm contracts and flattens
The volume of the thorax increases
Thoracic pressure falls below atmospheric pressure, so air moves into the lungs

Key terms in this question

inspiration · thorax