Similar to carbon, nitrogen is a necessary component of biological molecules. Some of these molecules include amino acids and nucleic acids. Although nitrogen (N2) is abundant in the atmosphere, most living organisms can not use nitrogen in this form to synthesize organic compounds. Atmospheric nitrogen must first be fixed, or converted to ammonia (NH3) by certain bacteria.Steps of the Nitrogen CycleAtmospheric nitrogen (N2) is converted to ammonia (NH3) by nitrogen-fixing bacteria in aquatic and soil environments. These organisms use nitrogen to synthesise the biological molecules they need to survive.NH3 is subsequently converted to nitrite and nitrate by bacteria known as nitrifying bacteria.Plants obtain nitrogen from the soil by absorbing ammonium (NH4-) and nitrate through their roots. Nitrate and ammonium are used to produce organic compounds.Nitrogen in its organic form is obtained by animals when they consume plants or animals.Decomposers return NH3 to the soil by decomposing solid waste and dead or decaying matter.Nitrifying bacteria convert NH3 to nitrite and nitrate.Denitrifying bacteria convert nitrite and nitrate to N2, releasing N2 back into the atmosphere.