Nitrogen cycle involves nitrogen fixation, assimilation and biosynthesis, decomposition, ammonification and nitrification.
Nitrogen fixation
In nitrogen fixation, the nitrogen-fixing bacteria like cyanobacteria can convert the atmospheric nitrogen N2 into ammonia NH3. The ammonia converted dissolves in the cytoplasm of the bacterial cells to form ammonium NH4+. The plants then use these ammonia stored in the bacteria to synthesize amino acids for proteins and genetic materials such as DNA. Other organisms treat plants as a source of nitrogen. They can gain nitrogen directly or indirectly from the plants for growth and development.
Title: Nitrogen Cycle
Ammonification and Nitrification
The decomposers, mainly bacteria and fungi, decompose nitrogenous waste and the remains of organisms back to ammonia NH3 which dissolves in the bacterial cytoplasm to form ammonium NH4+. This process is called ammonification. Some of the ammonium is utilized by the bacteria and the fungi for metabolism to support life and the other will be released into the environment, which can then be used by the plants again. Some bacteria can convert ammonium to nitrite NO2- and some bacteria can further convert the nitrite to nitrate NO3-. These processes of formation nitrites and nitrate are called nitrification. Both nitrites and nitrates can be taken up by plants and be used by other higher organisms again. Denitrifying bacteria can convert nitrate to N2O and then to N2 which is to be released into the atmosphere. This completes the whole cycle of nitrogen.