Aerobic Respiration

Aerobic respiration is the release of energy from glucose or another organic substrate in the presence of Oxygen. Strictly speaking aerobic means in air, but it is the Oxygen in the air which is necessary for aerobic respiration. Anaerobic respiration is in the absence of air.

Here is a molecular model of a glucose molecule. You do not need to memorise the diagram for you GCSE exam, but it should help you to understand that a molecule of glucose contains six atoms of Carbon (shown in blue), twelve atoms of Hydrogen (shown in green), and six atoms of Oxygen (shown in red).

A Glucose Molecule

In our tissues glucose can be broken down to release energy. The energy is used to make a substance called Adenosine Tri-Phosphate or ATP as it is usually called. ATP can provide energy for other processes such as muscle contractions.

Here is a balanced chemical equation for the process of aerobic respiration. You only need to memorise this for the Higher Tier GCSE paper, however I am sure that you really want a grade “A” so why not memorise it.

Balanced Chemical Equation for Aerobic Respiration

You should be able to see six carbon atoms on each side of the equation; One molecule of glucose contains six atoms of Carbon and six molecules of Carbon Dioxide each contain one atom of Carbon.

You should also be able to see that the Hydrogen is balanced. One molecule of Glucose contains twelve atoms of Hydrogen and six molecules of water each contain two atoms of Hydrogen.

Now look at the Oxygen. To make six molecules of Carbon Dioxide we need twelve atoms of Oxygen and to make six molecules of water we need another six atoms of Oxygen. That makes a total of eighteen atoms of Oxygen. The glucose already contains six atoms of Oxygen so the cell will need a further six molecules of Oxygen from the air.

The basic minimum knowledge for GCSE biology is the word equation given below. Even if you don’t understand it you can memorise it like a parrot.

Glucose + Oxygen = Carbon Dioxide + Water + Energy

Aerobic respiration takes place in almost all living things. It is easy to get rid of the Carbon Dioxide and excess water; this is excretion (the removal of the toxic waste products of metabolism), and maximum energy is released from the glucose.

Some organisms can respire in the absence of air: this is anaerobic respiration. This does not release so much energy and it produces much more toxic waste products. However, if Oxygen is not available, anaerobic respiration is better than nothing. When this happens in our muscles we produce lactic acid which gives you cramp. The bacteria in milk produce the same chemical when they turn it sour. “Lactic” means “of milk”. So lactic acid is the acid in sour milk. Yeasts produce alcohol which is also toxic. Eventually there will be so much alcohol that the yeast cannot survive.