Anaerobic Respiration
There are occasions when the cells undergoing respiration cannot get enough oxygen to perform aerobic respiration. For example when exercising vigorously the amount of oxygen getting to the muscles may be insufficient for aerobic respiration. If the cells still require energy then they need to respire without oxygen. This is anaerobic respiration.
Without oxygen the breakdown of the food is incomplete. This means less energy is released. There are two types of anaerobic respiration depending whether it takes place in an animal or a plant / fungi.
Anaerobic Respiration in Animals
In animals, anaerobic respiration produces lactic acid as the glucose is not fully broken down.
| Glucose |  |
Lactic acid + energy |
If the lactic acid builds up it can stop the muscles from working, causing cramp. This lactic acid needs to be broken down. This requires oxygen. Respiring in this way builds up an oxygen debt which must be repaid in order to get rid of the lactic acid. As a result, animals cannot respire for very long without oxygen.
Anaerobic Respiration in Plants / Fungi
When plants or fungi respire they produce ethanol (alcohol) and carbon dioxide.
| Glucose | |
Carbon Dioxide + Ethanol + energy |
A build up of ethanol can be toxic. Some organisms, such as yeast, respire in this way all the time. Yeast is used to make alcoholic drinks. The process is called fermentation.
Yeast is also used in bread making as it gives of carbon dioxide gas which makes the bread rise, giving it a light and fluffy texture.
