Nitrogen Cycle

Nitrogen is essential for all forms of life on Earth. It is part of proteins and genes. Proteins are used not only to make muscles, skin, hair and other connective tissue, but also to form the enzymes which are the chemical workers in every cell. Genes carry the information needed to build proteins. Both these vital chemicals contain nitrogen, so life cannot work without it.

Nitrogen makes up about 80% of the atmosphere of Earth. Unfortunately it is in a form which cannot easily be absorbed by living cells. In air nitrogen is a molecule containing two tightly bound nitrogen atoms. Life needs to split these two atoms apart.

There are very few cells on Earth that are able to do this. Only some bacteria (germs) are able to do this. They are called nitrogen fixing bacteria, and they include the blue-green bacteria and a few others.

All higher plants and animals rely upon these nitrogen fixers to give them nitrogen in a form they can use. Some plants achieve this by holding these bacteria in nodules on their roots. Examples are the legumes such as peas and beans.

Animals get their nitrogen from the plants they eat. The only animal able to fix nitrogen is man, who uses his industrial processes and ingenuity.

All molecules in living things are constantly recycled. The nitrogen in proteins and genes in an animal is eventually broken down to urea, and excreted in the urine. This is then converted into ammonia by other bacteria. Some of it is then converted back into atmospheric ammonia by bacteria in the soil.