GCSE Biology · AQA 8461 · Topic 4.4.2
Respiration
Key points
- Aerobic respiration: glucose + oxygen → carbon dioxide + water. . It happens mainly in mitochondria.
- Anaerobic respiration in muscles: glucose → lactic acid. In plants and yeast: glucose → ethanol + carbon dioxide (fermentation, used in bread and beer).
- Anaerobic respiration releases much less energy because glucose is only partly broken down.
- During exercise, heart rate, breathing rate and breath volume rise to supply more oxygen. Lactic acid builds up and muscles fatigue.
- The oxygen debt is the extra oxygen needed after exercise to react with lactic acid; blood carries it to the liver to be turned back into glucose.
- Metabolism includes making starch, cellulose, glycogen, lipids and proteins, respiration, and breaking excess protein into urea.
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Respiration releases the energy every cell needs to stay alive. It happens all the time in every living cell, including plant cells, and can take place with or without oxygen, with very different results.
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