The physical characteristics and behaviour of all living organisms are intimately associated with their biochemistry.

All of the chemical reactions that occur within a cell or organism are known as the metabolism. This can be very complex.

99% of the atoms in an organism are Hydrogen, Carbon, Oxygen and Nitrogen. These elements combine to form four groups of Biological molecules which are only found in living cells.

These groups are:

• Carbohydrates

• Proteins

• Lipids

• Nucleic acids

Other molecules of significance to living organisms are:

• inorganic ions

• water