Nitrogen is the basic unit of life. As DNA also contains nitrogen. So if there is no nitrogen present in the atmosphere, there is no life. Plants also use nitrogen to form proteins. Moreover, in humans, nitrogen in hemoglobin form ring. It is also used in formation of enzymes, hormones etc. Utilization of Nitrogen is too much, but the amount of nitrogen in the environment remains the same. It never increases or decreases. It always remains 78% of atmosphere. This is regulated by a series of steps in the cycle.
Nitrogen cycle regulate the amount of nitrogen in atmosphere. It is the process through which nitrogen is converted into nitrogenous compounds and then converted back to atmospheric nitrogen to the environment. It consists of the following steps;
1. Ammonification.
2. Nitrification.
3. Nitrogen Fixation.
4. Assimilation.
5. Denitrification.
Ammonification:
Atmospheric nitrogen is converted into ammonia or ammonium ions in ammonification.
Atmospheric nitrogen is converted into amino acids, carbon dioxide and energy by the bacteria or fungi. These amino acids are converted into ions. These microorganisms are saprophytic, which feed upon dead organic material such as animal excreta and dead plant' leaves.
It is done in aerobic environment.
Nitrification:
It is the conversion of ammonia into nitrates. It can be done in two steps, first ammonia is converted into nitrites, and then these nitrites are converted to nitrates.
Two groups of bacteria work to convert ammonia into nitrates. Nitrosomonas convert ammonia into nitrites, and these nitrites are converted into nitrates by the group of bacteria called Nitrobacter.
It is also done in aerobic environment, so the soil is good for agriculture.
Nitrogen Fixation:
As plants and animals cannot directly absorb atmospheric nitrogen. They absorb nitrogen in the form of nitrogenous compounds such as nitrates. To do so, nitrogen is fixed by three following methods;
1. Atmospheric nitrogen fixation: About 5 to 8% nitrogen is fixed by this method. Lightening causes the nitrogen and oxygen to form nitrogen oxides. Through the rain, these oxides reach the soil from where plant get it.
2. Industrial nitrogen fixation: It includes the synthesis of fertilizers having nitrogenous compounds.
3. Biological nitrogen fixation: In this method nitrogen is fixed by using living organisms such as bacteria i.e. Azotobacter, Rhizobium (present in the root nodules of leguminous plants). About 60% atmospheric nitrogen is converted into nitrogenous compounds.
Assimilation:
In this, the nitrogenous compounds are utilized in living bodies. Microorganisms can absorb atmospheric nitrogen. Plants absorb nitrogenous compounds from soil and then use these compounds to form proteins. Animals feed upon these plants and other animals and get nitrogen. Then this nitrogen is utilized in many human processes such as synthesis of proteins, to produce hormones and neurotransmitters etc.
Denitrification:
Denitrification as a name shows that the breakdown of nitrates into atmospheric nitrogen. In the absence of oxygen, aerobic bacteria, such as Pseudomonas, breakdown the nitrogenous compounds into atmospheric nitrogen and oxygen. For their respiration, bacteria use this oxygen and release oxygen back to atmosphere.
Concludingly, the nitrogen' percentage in the environment remains the same because of this cycle. This cycle maintains the nitrogen and their nitrogenous compounds in the atmosphere.
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