Respiration
Respiration is the chemical reactions in cells that break down nutrient molecules and release energy for metabolism 1. It happens continuously in every living cell, not only in animals or when breathing.
Aerobic and Anaerobic
| Feature | Aerobic respiration | Anaerobic respiration |
|---|---|---|
| Oxygen | Required | Not used |
| Word equation | glucose + oxygen → carbon dioxide + water | yeast: glucose → alcohol + carbon dioxide muscle: glucose → lactic acid |
| Energy yield | Much greater per glucose molecule | Much less per glucose molecule |
glucose ──(aerobic, O2)──► CO2 + H2O + much energy
glucose ──(anaerobic)────► alcohol + CO2 (yeast) / lactic acid (muscle) + little energyUses of the Released Energy
The syllabus lists muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses, and the maintenance of a constant body temperature 1. Ion uptake by root hairs is an active-transport case that consumes this energy.
Lactic Acid and Oxygen Debt
During vigorous exercise, muscle respires anaerobically and lactic acid accumulates; afterwards extra oxygen is taken in to oxidise it, partly in the liver. Respiration is an exothermic change: it transfers energy to the surroundings as heat.
Related
- Living Thing - Entity carrying out all seven life processes.
- Organism - Individual living thing.
- Nutrition - Supplies the molecules broken down.
- Mitochondrion - Organelle where aerobic respiration occurs.
- Movement - Powers muscle contraction.
- Excretion - Removes carbon dioxide.
- Exothermic Change - Energy-releasing, like respiration.
- Biology - Cambridge IGCSE life-science area.
Footnotes
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Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 - Respiration (1.1b), uses of energy (12.1), aerobic (12.2) and anaerobic respiration with oxygen debt (12.3). ↩ ↩2