Describe nitrogen cycle with help of labelled diagram
Answers
Nitrogen is both the most abundant element in the atmosphere and, as a building block of proteins and nucleic acids such as DNA, a crucially important component of all biological life. 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 several stages:
Nitrogen fixation
Atmospheric nitrogen occurs primarily in an inert form (N2) that few organisms can use; therefore it must be converted to an organic – or fixed – form in a process called nitrogen fixation. Most atmospheric nitrogen is ‘fixed’ through biological processes. First, nitrogen is deposited from the atmosphere into soils and surface waters, mainly through precipitation. Once in the soils and surface waters, nitrogen undergoes a set of changes: its two nitrogen atoms separate and combine with hydrogen to form ammonia (NH4+). This is done by microorganisms that fall into three broad categories: bacteria living in symbiotic relationships with certain plants, free anaerobic bacteria, and algae. Crops, such as alfalfa and beans, are often planted in order to remedy the nitrogen-depletion in soils, and nitrogen-fixing bacteria employ an enzyme, known as nitrogenase, to split atmospheric nitrogen molecules into individual atoms for combination into other compounds.
A small amount of nitrogen is ‘fixed’ through a process of high energy fixation that occurs primarily as lighting strikes converting atmospheric nitrogen into ammonia (NH4+) and nitrates (NO3-). Nitrogen can also be fixed through man-made processes, primarily industrial processes that create ammonia and nitrogen-rich fertilizers.
Nitrification
While ammonia can be used by some plants, most of the nitrogen taken up by plants is converted by bacteria from ammonia – which is highly toxic to many organisms – into nitrite (NO2-), and then into nitrate (NO3-). This process is called nitrification, and these bacteria are known as nitrifying bacteria.
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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Answer:
Nitrogen is essential nutrient for the survival of living being is found in protein like DNA and RNA. Nitrogen cannot be used directly from the atmosphere and have to be converted into nitrates and nitrites by certain nitrogen fixing bacteria. These bacteria are found in root noodles of leguminous, plant that give us pulses.
Another method through which the nitrogen in our environment can be converted into nitrates or nitrites is physical process of lightning the high pressure and temperature during the lightning create the nitrogen into oxide and nitrogen into oxide of nitrogen then dissolve in water bodies, thus forming nitrous and nitric acid.
Once nitrogen is converted to the useful form of nitrates and nitrites they can be used for the plant for use them to produce amino acids, which are then used to make protein other Complex compounds that requires nitrogen are also made of these through some Complex bio chemical process. These proteins by animal once these plants and animal die and and ded buried in the soil bacteria convert this protein back to nitrites and nitrates. The certain kind of bacteria converts protein to elemental nitrogen. Thus completing a complete nitrogen cycle.
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