Living things need nitrogen to produce amino acids that allow the organism to live and grow. These amino acids are used to make proteins that build tissues and organs and regulate cellular function.
Free nitrogen comprises approximately 78 percent of the gas in the atmosphere. Before living things are able to use free nitrogen it must be fixed by bacteria. Nitrogen-fixing bacteria combine free nitrogen with other elements to form nitrogen compounds that can be absorbed through a plant's root system. Once a plant absorbs the nitrogen compound, it uses it to produce compounds that can be digested by animals. As a plant or animal decays, the remaining nitrogen in its body is returned to the nitrogen cycle.
When an area has a nitrogen deficiency, a chemical fertilizer can be added to the soil. Chemical fertilizers are prepared using ammonia, a compound containing nitrogen and hydrogen. Nitrogen can also be added to the soil through organic means.
Besides fertilization, nitrogen compounds have many other uses. They are often used in the production of plastics, dyes and explosives or to make photographic film. Nitrogen compounds are also used in the curing and storage of food, in sulfa drugs, in vitamins and in synthetic fabrics.