Describe the roles of the intercostal muscles and diaphragm during inhalation in humans.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The intercostal muscles contract during inhalation, pulling the ribcage upwards and outwards. The diaphragm contracts and flattens, moving downwards. These movements increase the volume of the thorax, lowering the air pressure inside the lungs so air flows in.
Examiner tips
- Use the verb ‘contract’ for both muscle groups; link movement to volume change; mention pressure decrease and airflow; keep answer concise to fit 4 marks
Common mistakes
- Forgetting to state that the diaphragm moves downwards; describing the ribcage movement as ‘inward’ instead of ‘upwards and outwards’; omitting the link between increased volume, lower pressure and air inflow
Mark scheme (4 marks)
- The intercostal muscles contract during inhalation
- Contraction of the intercostal muscles moves the ribcage upwards and outwards
- The diaphragm contracts and flattens (moves downwards)
- These movements increase the volume of the thorax / chest cavity, which decreases the air pressure inside the lungs, so air moves in
Key terms in this question
intercostal muscles · diaphragm · inhalation
Related
- All Pearson Edexcel International GCSE Biology (4BI1) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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