Cambridge IGCSE·Co-ordinated Sciences 0654·Biology
Gas Exchange Respiration
Key knowledge — Gas Exchange Respiration
Formulas & equations
Aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+energy/ATP)Anaerobic respiration (animals): C₆H₁₂O₆ → 2C₃H₆O₃ (lactic acid, less energy)Anaerobic respiration (yeast): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (ethanol + CO₂)
Key facts & rules
- Aerobic respiration releases ~38 ATP per glucose. Anaerobic releases ~2 ATP per glucose.
- Oxygen debt: extra O₂ needed after anaerobic respiration to break down lactic acid.
- Alveoli: millions in lungs; large surface area, moist, thin walls (one cell thick), rich blood supply.
- Breathing in (inhalation): diaphragm contracts and flattens, intercostal muscles raise ribs, thorax volume increases, pressure decreases.
- Breathing out (exhalation): diaphragm relaxes, ribs fall, thorax volume decreases, pressure increases.
- Trachea → bronchi → bronchioles → alveoli.
- Smoking damages cilia, causes excess mucus, destroys alveolar walls (emphysema), and increases cancer risk.
IGCSE Biology — Gas exchange & respiration
1340 Cambridge IGCSE 0654 biology past paper questions on gas exchange & respiration, organised by subtopic. Pick a subtopic to start practising.
About gas exchange & respiration on IGCSE 0654
Gas exchange in humans, the features of an efficient gas-exchange surface, and aerobic and anaerobic respiration with their equations.