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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).
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.
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 Oxygen.
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.
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