Explain how air moves from the atmosphere into the lungs during inhalation.

WJEC GCSE Biology (Wales) — 1.2.2 The respiratory system · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

The intercostal muscles contract and the diaphragm contracts, raising the ribcage and flattening the diaphragm. This increases the volume of the thorax, lowering the pressure inside the lungs below atmospheric pressure. Air therefore moves into the lungs down the pressure gradient, from high pressure outside to low pressure inside.

Examiner tips

Use the exact sequence: muscle contraction → volume increase → pressure drop → airflow.
Show the cause–effect chain and mention the pressure gradient explicitly.
Keep the answer concise – 4 points can be covered in 2–3 short sentences.
Use UK spelling (e.g. ‘diaphragm’).

Common mistakes

Omitting the diaphragm or intercostal muscles; only mentioning the ribcage.
Failing to state that lung pressure falls below atmospheric pressure.
Describing airflow without linking it to the pressure gradient.

Mark scheme (4 marks)

The intercostal muscles contract / the diaphragm contracts
The ribcage moves upwards and outwards / the diaphragm flattens, increasing the volume of the thorax (chest cavity)
The pressure inside the lungs decreases (below atmospheric pressure)
Air moves into the lungs down the pressure gradient / from high pressure outside to low pressure inside

Key terms in this question

inhalation