Nitrogen is an essential nutrient for life yet in its gaseous state is almost entirely unusable to life forms. It must first be converted or ‘fixed’ into usable forms by the conversion process of fixation. Specialized bacteria function in nitrogen fixation, making the element bioavailable. Once it is fixed it can be absorbed and incorporated into plants which are subsequently consumed and incorporated into animals within the food web. There are also bacteria that perform the reverse process called denitrification and convert nitrogen into its gaseous form. The process of nitrogen being fixed, used by plants and animals, and later returned to the atmosphere is referred to as the nitrogen cycle.
It is also important to note that nitrogen is the most abundant element in our planet and it comprises about 78% of the atmosphere.