Unlike aerobic respiration, anaerobic respiration does not need oxygen. It is the release of a relatively small amount of energy in cells by the breakdown of food substances in the absence of oxygen.
Anaerobic respiration happens in muscles during hard exercise:
glucose → lactic acid
C6H12O6 → 2C3H6O3
Glucose is not completely broken down, so much less energy is released than during aerobic respiration.
This causes an oxygen debt - known as excess post-exercise oxygen consumption (EPOC) - that needs to be ‘repaid’ after the exercise stops. This is why we keep on breathing deeply for a few minutes after we have finished exercising.
Anaerobic respiration also happens in plant cells and some microorganisms. Anaerobic respiration in yeast is used during brewing and bread-making:
glucose → ethanol + carbon dioxide
C6H12O6 → 2C2H5OH + 2C02
Ethanol is the alcohol found in alcoholic drinks like beer and wine. In bread-making, bubbles of carbon dioxide gas expand the dough and help the bread rise.
The table summarises some differences between the two types of respiration.
|End product(s)||Carbon dioxide and water||Animal cells: lactic acid. Plant cells and yeast: carbon dioxide and ethanol|
|Energy released||Relatively large amount||Relatively small amount|
Aerobic respiration releases 19 times more energy than anaerobic respiration from the same amount of glucose.