Respiration
Biology: AQA GCSE Higher, topic 4.2.2
Respiration
Respiration is an exothermic reaction (releases energy) that supplies all the energy needed by living organisms. This reaction happens continuously in all living cells. The reaction can be aerobic (with oxygen) or anaerobic (without oxygen).
Aerobic respiration (with oxygen)
- In aerobic respiration, glucose reacts with oxygen in the mitochondria of cells to give carbon dioxide, water and energy.
- Glucose + oxygen → carbon dioxide + water (+ energy)
- C6H12O6 + 6O2 → 6CO2 + 6H2O (+ energy)
Anaerobic respiration in animals
- Glucose is not broken down completely, making it a less efficient way of transferring energy than aerobic respiration.
- In animals, glucose is converted to lactic acid:
- Glucose → lactic acid
- Anaerobic respiration happens when insufficient (not enough) oxygen reaches the muscles during periods of intense activity.
Anaerobic respiration in plants
- In plant and yeast cells, glucose is converted into ethanol and carbon dioxide.
- Glucose → ethanol + carbon dioxide
- In yeast cells, this is called fermentation. This is an important step in the manufacture (making) of both bread and alcohol.
Test yourself on Respiration
Why do muscle cells respire anaerobically during intense exercise?
Why is anaerobic respiration in animals less efficient than aerobic respiration?
Which statement correctly compares anaerobic respiration in animal cells with anaerobic respiration in yeast cells?