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Aerobic respiration


Aerobic respiration is summarised by the equation -

Glucose + Oxygen = Carbon dioxide + Water + ENERGY

Anaerobic respiration

Anaerobic respiration is respiration without oxygen. This happens when cells may be short of oxygen e.g. during vigorous exercise.

Anaerobic respiration uses glucose. The waste product made is LACTIC ACID. This lactic acid can cause harm if it builds up in your body.

The body needs to break down lactic acid. It needs oxygen to do this. The extra oxygen that is needed for this is called the OXYGEN DEBT. This is why after heavy exercise you still breathe heavily even after the exercise has stopped. You are trying to re-pay the oxygen debt i.e. you need to take in extra oxygen to break down the lactic acid.


The energy that is released in respiration is used -

1. To enable muscles to contract.

2. To build up larger molecules from smaller ones.

3. To keep us at a steady body temperature in colder surroundings.

The energy that is released during respiration is also used in the active transport of materials across boundaries.

Anaerobic respiration - the detail.


When you do vigorous exercise and your body can not supply enough oxygen to your muscles, they start doing anaerobic respiration. Glucose is converted to energy and lactic acid.

The lactic acid builds up in the muscles, which gets painful. The muscles become tired or "fatigued". This makes your muscles less efficient and so they do not contract as well as they ought to. One advantage is that you can keep on using your muscles for a while longer, however, after resorting to anaerobic respiration, when you stop you will have an oxygen debt.

You have to "repay" the oxygen, which you didn't manage to get to your muscles in time, because your lungs, heart and blood could not keep up with the demand during exercise.

You have to keep breathing hard for a while after you stop to get oxygen into your muscles to convert the painful lactic acid which has built up to harmless carbon dioxide and water. 

Anaerobic respiration is the incomplete breakdown of glucose to lactic acid. Because the breakdown of glucose is incomplete, much less energy is released than during aerobic respiration.

When high levels of carbon dioxide and lactic acid are detected in the blood (by the brain), the pulse and breathing rate are increased automatically to try and rectify the situation.


A good measure of fitness is how quickly you can recover to normal breathing and pulse rate after doing exercise. This is known as your recovery time.

Increased muscle activity requires glucose and oxygen to be supplied at a faster rate and increases the rate of removal of carbon dioxide and heat from muscle tissues.

Anaerobic exercise

Candidates should be able to predict the effect of muscles and bones on movement in unfamiliar situations.

Regular exercise:

· keeps muscles toned, so the fibres are slightly tensed and ready to contract;

· increases muscle strength and avoids muscles feeling stiff and sore after exercise;

· keeps joints working smoothly;

· maintains an efficient supply of blood to the muscles, the heart and the lungs.