Nitrogen is important to life because it comprises approximately 80 percent of the Earth's atmosphere and is present in all living things as a part of proteins and DNA, according to the Marine Biological Laboratory. Nitrogen is present in the amino acids that make up proteins. It is also essential to reproduction because it is present in the nucleic acids in genetic material, or DNA.
According to HowStuffWorks, the nitrogen used by living things must be fixed nitrogen rather than free nitrogen. Fixed nitrogen is primarily created by blue-green algae and certain types of bacteria. The bacteria and blue-green algae take nitrogen from the air and combine it with other elements so that these compounds can be utilized by living things through the nitrogen cycle. The nitrogen cycle contributes to life-sustaining processes. For example, bacteria in soil create the nitrogen compounds that assist in plant growth. As a result, nitrogen is an integral part of the plant. The plant is consumed by animals, where the nitrogen moves through the digestive process through the assistance of bacteria in the animal's digestive system that convert unused nitrogen compounds in the plant from waste back to nitrogen gases, completing the cycle, according to Live Science.