Describe the role of cilia and mucus in protecting the gas exchange system from damage caused by pathogens and particles in inhaled air.

Pearson Edexcel International GCSE Biology (4BI1) — 2.9 Gas exchange: 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)

Goblet cells in the lining of the trachea and bronchi secrete mucus.
Mucus traps pathogens, dust, particles and microorganisms that are inhaled.
Cilia on the epithelial cells beat rhythmically.
The ciliary action moves the mucus, together with the trapped material, towards the throat where it can be swallowed or expelled.

Examiner tips

  • Use the exact terms ‘goblet cells’, ‘mucus’, ‘cilia’, ‘beat rhythmically’, ‘move mucus to the throat’
  • Show the causal link: mucus traps → cilia move → removal from lungs
  • Keep the answer concise – 4 marks, one point each

Common mistakes

  • Confusing cilia with mucus as the trapping mechanism
  • Omitting the role of goblet cells in mucus production
  • Using vague verbs such as ‘clean’ instead of ‘beat rhythmically’

Mark scheme (4 marks)

  1. Goblet cells / lining of the trachea and bronchi produce mucus
  2. Mucus traps pathogens / dust / particles / microorganisms
  3. Cilia beat / move rhythmically
  4. Cilia move the mucus (with trapped particles / pathogens) towards the throat / mouth to be swallowed or expelled

Key terms in this question

cilia · mucus · pathogens

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