B9.3 Anaerobic respiration

• When you exercise a lot, your muscle cells may become short of oxygen. Although you increase your heart and breathing rates, sometimes the blood cannot supply oxygen to the muscles fast enough. When this happens, energy from the breakdown of glucose can still be transferred to the muscle cells. They use anaerobic respiration, which takes place without oxygen.
• Anaerobic Respiration is not as efficient as aerobic respiration. Because the glucose molecules are not broken down completely in animal cells, the end product of aerobic respiration is lactic acid instead of carbon dioxide and water. As well as this, far less energy is transferred than during aerobic respiration.
• glucose → lactic acid (energy transferred to the environment)
• After exercise, oxygen is still needed to convert the accumulated lactic acid into glucose. The amount of oxygen needed is known as oxygen debt.
• Plants and microorganisms can also respire without oxygen, however instead of forming lactic acid, they form carbon dioxide and ethanol. Some microorganisms form lactic acid during anaerobic repsiration- the bacteria used to form yoghurts, for example. Other microorganisms, including yeast, form ethanol and carbon dioxide. Anaerobic repsiration in yeast cells are known as fermentation.
• glucose → ethanol + carbon dioxide (energy transferred to the environment)