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DMPQ: What is Nitrogen cycle. Explain its various stages. (science)

RAS/RTS Prelims and Mains Exam Preparation

The nitrogen cycle is a complex biogeochemical cycle in which nitrogen is converted from its inert atmospheric molecular form (N2) into a form that is useful in biological processes.

The Nitrogen cycle contains various stages:

  • Nitrogen fixation:

Inert form of Nitrogen is fixed and converted into organic form in a process called nitrogen fixation. Most atmospheric nitrogen is fixed through biological process.  Bacteria, free anaerobic bacteria and algae converts it nitrogen into ammonia(NH4+). An enzyme nitrogenase is used to fix nitrogen.

A small amount of N2 is fixed through a process of high energy fixation that occurs primarily as lighting strikes converting atmospheric nitrogen into ammonia(NH4+) and Nitrates ( NO-3) . Nitrogen can also be fixed through man made processes that create ammonia  and nitrogen rich fertilisers.

 

  • Nitrification

The nitrogen cycle is a complex biogeochemical cycle in which nitrogen is converted from its inert atmospheric molecular form (N2) into a form that is useful in biological processes.

 

  • Assimilation

Nitrogen compounds in various forms, such as nitrate, nitrite, ammonia, and ammonium are taken up from soils by plants which are then used in the formation of plant and animal proteins.

 

  • Ammonification

When plants and animals die, or when animals emit wastes, the nitrogen in the organic matter reenters the soil where it is broken down by other microorganisms, known as decomposers. This decomposition produces ammonia which is then available for other biological processes.

  • Denitrification

Nitrogen makes its way back into the atmosphere through a process called denitrification, in which nitrate (NO3-) is converted back to gaseous nitrogen (N2). Denitrification occurs primarily in wet soils where the water makes it difficult for microorganisms to get oxygen. Under these conditions, certain organisms – known as denitrifiying bacteria – will process nitrate to gain oxygen, leaving free nitrogen gas as a byproduct.

 

 

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