Explain nitrogen cycle

The nitrogen cycle involves three major steps: Nitrogen Fixation, Nitrification, and Denitrification. It is a cycle within the biosphere which involves the atmosphere, hydrosphere, and lithosphere. Nitrogen is found in several locations, or reservoirs. It is most prevalent in sediments and rocks, second in the atmosphere (78%).

Neither plants or animals can obtain nitrogen directly from the atmosphere. Instead, they depend on a process known as Nitrogen Fixation. Key players in this process are legumes and the Symbiotic Bacteria which are associated with the legume's root nodules. These bacteria are known as nitrogen-fixing bacteria. These organisms convert nitrogen in the soil to ammonia, which can then be taken up by plants. This process also occurs in aquatic ecosystems, where cyanobacteria participate.

After nitrogen has been fixed, other bacteria convert it into nitrate, in a process known as nitrification. In the first step of this process, Nitrosomonas convert ammonia into nitrite, and in the second step, nitrite is converted into nitrate, by Nitrobacter. This nitrate is then consumed by plants.

The final aspect of the nitrogen cycle is the process of denitrification. This process is performed by a variety of microscopic bacteria, fungi, and other organsims. Nitrates in the soil are broken down by these organsisms, and nitrogen is released into the atmosphere. This complete the cycle.