4.1 Aerobic Respiration
Aerobic respiration takes place in the mitochondria.
It involves chemical reactions that use oxygen and sugar and release energy:
glucose + oxygen --> carbon dioxide + water
The energy released is used to build large molecules from smaller molecules and allows muscles to contract.
In mammals and birds it enables them to maintain a constant body temperature.
During exercise, the heart rate increases to supply more oxygen.
4.2 The effect of exercise on the body
When you exercise, your muscles need more energy so they can contract.
You need to increase the rate at which oxygen and glucose reach the muscle cells for aerobic respiration.
You also need to remove the extra waste carbon dioxide produced more quickly.
The heart rate increases and the blood vessels supplying the muscles dilate. This allows more blood containing oxygen and glucose to reach the muscles.
Your breathing rate and depth of each breath also increase. This allows a greater uptake of oxygen and release of carbon dioxide at the lungs.
Muscles store glucose as glycogen. The glycogen can be converted back to glucose for use during exercise.
ANAEROBIC RESPIRATION: glucose --> lactic acid
4.3 Anaerobic Respiration
If muscles work hard for a long time they become fatigued and don't contract efficiently. If they don't get enough oxygen, they will respire anaerobically.
Anaerobic respiration is respiration without oxygen. Glucose is incompletely broken down to form lactic acid.
This requires less energy than aerobic respiration.
After exercise, oxygen is still needed to break down the lactic acid which has built up.
The amount of oxygen needed is known as oxygen debt.
The build up of lactic acid can cause muscle fatigue.
Warming down after exercise helps to break down lactic acid.