How to Revise IGCSE Biology Topic 11: Gas Exchange
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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Key point
Memorise alveoli adaptations (4 features linked to function). Know the mechanics of inhalation and exhalation. Understand the effects of tar, nicotine, and carbon monoxide from smoking.
Topic 11 covers the structure of the gas exchange system, how alveoli are adapted for efficient gas exchange, the mechanics of breathing (ventilation), and the harmful effects of smoking. Alveoli adaptations are one of the most frequently tested topics.
Priority 1: Alveoli adaptations
Alveoli are adapted for efficient gas exchange: large surface area (millions of alveoli), thin walls (one cell thick: short diffusion distance), rich blood supply (dense capillary network maintains concentration gradient), moist lining (gases dissolve before diffusing).
Priority 2: Breathing mechanics
Inhalation: intercostal muscles contract → ribs move up and out; diaphragm contracts → flattens and moves down; thorax volume increases → pressure decreases → air drawn in. Exhalation: intercostal muscles relax → ribs move down and in; diaphragm relaxes → domes up; thorax volume decreases → pressure increases → air pushed out.
Priority 3: Effects of smoking
Tar: carcinogen → lung cancer; damages cilia → mucus accumulates → chronic bronchitis. Nicotine: addictive, raises heart rate and blood pressure → increased risk of coronary heart disease. Carbon monoxide: binds to haemoglobin → reduces oxygen-carrying capacity of blood.
Frequently asked questions
Is breathing the same as respiration?
No. Breathing (ventilation) is the physical movement of air in and out of the lungs. Respiration is the chemical reaction inside cells that releases energy from glucose. Do not confuse them.
Put the guide into practice
Questions and practical resources
Use a fresh question to check whether the idea can be applied without prompts.