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Respiration - Coggle Diagram
Respiration
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Oxygen Debt
When a period of exercise is over, lactic acid must be removed. The body's tolerance of lactic acid is limited.
Lactic acid is taken to the liver by the blood, and either: oxidised to carbon dioxide and water, or converted to glucose, then glycogen.
These processes require oxygen. This is why, when the period of activity is over, a person’s breathing rate and heart rate do not return to normal straightaway.
The amount of oxygen required to remove the lactic acid, and replace the body's reserves of oxygen, is called the oxygen debt.
Anaerobic Respiration
Most organisms cannot respire without oxygen but some organisms and tissues can continue to respire if the oxygen runs out. These organisms and tissues use the process of anaerobic respiration.
Plants and yeast
Some plants, and some fungi such as yeast can respire anaerobically – it's preferable to release less energy but remain alive.
Glucose in yeast cells is converted to carbon dioxide and ethanol, which we refer to simply as 'alcohol':
glucose → ethanol + carbon dioxide + energy released
Yeast
Yeast can also be used to produce bread. Yeast respires using sugar added to the dough. Bubbles of carbon dioxide make the bread rise. The alcohol that’s produced evaporates as the bread is baked.
Yeast is used to make alcoholic drinks. When yeast cells are reproducing rapidly during beer or wine production, the oxygen runs out. The yeast switches to anaerobic respiration. Ethanol and carbon dioxide are produced.
Plants
Certain plants, and plant cells also respire anaerobically. These include plants that grow in marshes, where oxygen concentrations will be low.
Animals
Animal muscle can respire anaerobically for short periods of time – even though the process is relatively inefficient, it's better to continue respiring and be able to run away from danger – or run a race.
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Aerobic Respiration
Respiration using oxygen to break down food molecules is called aerobic respiration. Glucose is the molecule normally used for respiration – it is the main respiratory substrate. Glucose is oxidised to release its energy.
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Response to exercise
Muscles need energy to contract. While exercising, the muscles need additional energy as:
the heart rate increases, to supply the muscles with extra oxygen and remove the carbon dioxide produced
the breathing rate and volume of each breath increases to bring more oxygen into the body and remove the carbon dioxide produced
This build-up of lactic acid produces an oxygen debt.
As body stores of glycogen become low, the person suffers from muscle fatigue.
If insufficient oxygen is available to the muscles, for instance the exercise is vigorous and/or prolonged, the heart and lungs are unable to supply sufficient oxygen. Muscles begin to respire anaerobically. Lactic acid is produced from glucose, instead of carbon dioxide and water. Muscles continue to contract, but less efficiently.