Explain why cigarette smoking increases the risk of lung infections and reduces the efficiency of gas exchange in the lungs.

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)

Smoking damages the cilia lining the airways, so mucus and trapped pathogens are not cleared, increasing infection risk.

It also breaks down the walls between alveoli, reducing the surface area for gas exchange.

With less surface area, less oxygen diffuses into the blood and less carbon dioxide leaves, so gas exchange is less efficient.

Examiner tips

Use the exact terms "cilia", "alveoli", "surface area" and "diffusion". Show the causal chain: damage → reduced clearance → infection; damage → reduced surface area → reduced diffusion. Keep each point brief – one sentence per point for 4 marks.

Common mistakes

Writing that smoking only causes infections, ignoring the gas‑exchange effect. Using vague phrases like "lung damage" instead of specifying cilia or alveolar walls. Omitting the word "diffusion" when describing gas exchange.

Mark scheme (4 marks)

Smoking damages or destroys cilia (on the lining of the airways/trachea/bronchi)
Without functioning cilia, mucus and trapped pathogens/bacteria/viruses are not swept away from the lungs, increasing risk of infection
Smoking causes the walls between alveoli to break down, reducing the surface area available for gas exchange
Reduced surface area means less oxygen can diffuse into the blood (and less carbon dioxide can diffuse out), so gas exchange is less efficient

Key terms in this question

gas exchange