Aerobic and Anaerobic Respiration — AQA GCSE Biology
Respiration releases energy from glucose in every living cell. It can occur with or without oxygen.
Respiration basics
Respiration is an exothermic reaction that happens in all living cells and releases energy (stored in ATP). It is not the same as breathing. The energy is used for movement, keeping warm, and building larger molecules.
Aerobic respiration
Uses oxygen and releases the most energy. It takes place mainly in the mitochondria.
glucose + oxygen → carbon dioxide + water $$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$$
Anaerobic respiration
Occurs without oxygen and releases much less energy (glucose is not completely broken down).
- In muscle cells: glucose → lactic acid.
- In plants and yeast: glucose → ethanol + carbon dioxide. In yeast this is fermentation, used in baking and brewing.
Comparing them
| Aerobic | Anaerobic | |
|---|---|---|
| Oxygen | needed | not needed |
| Energy released | a lot | a little |
| Products (animals) | CO₂ + water | lactic acid |
| Site | mitochondria | cytoplasm |
Exam tips
- Respiration is exothermic and happens in all cells — not the same as breathing.
- Learn the aerobic equation (word and symbol).
- Anaerobic respiration gives lactic acid (muscles) or ethanol + CO₂ (yeast/plants).
- Aerobic releases more energy than anaerobic.