Describe how air moves from the atmosphere into the alveoli during inhalation.

Eduqas GCSE Biology — 1.2.2 The respiratory system · 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 intercostal muscles and diaphragm contract.
2. The ribcage moves upwards and outwards and the diaphragm flattens.
3. The volume of the thorax increases, lowering the pressure inside the chest cavity below atmospheric pressure.
4. Air flows along the pressure gradient, entering through the trachea, bronchi, bronchioles and reaching the alveoli.

Examiner tips

Use the exact sequence of events (muscle contraction → ribcage movement → pressure change → airflow).
Show the pressure relationship (inside < outside).
Mention the airway pathway to the alveoli.

Common mistakes

Omitting the diaphragm or intercostal muscles.
Failing to state that pressure inside falls below atmospheric.

Mark scheme (4 marks)

The intercostal muscles (and diaphragm) contract
The ribcage moves upwards and outwards / the diaphragm flattens
The volume of the thorax / chest cavity increases, causing air pressure inside to decrease / fall below atmospheric pressure
Air moves in along a pressure gradient / air flows in from high to low pressure / air enters through the trachea, bronchi, bronchioles to the alveoli

Key terms in this question

inhalation · alveoli