Question

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Name the four processes of the nitrogen cycle and describe what happens in each process.

Answer 1

Nitrogen is very important to life and it cycles through our biosphere. 78% of the earth atmosphere is contributed by molecular nitrogen.

The five main process involved in nitrogen cycle are :

1. Nitrogen fixation

As you know that, plant need nitrogen for its metabolic activities. But plants cannot take up nitrogen directly. So nitrogen from atmosphere is fixed mainly by two ways.

i) Nitrogen fixation by Lightning

ii) Nitrogen fixation by Nitrogen fixing bacteria

Most of the Nitrogen fixation is done by free living or symbiotic bacteria which have the nitrogenase enzyme in them.

Example of free-living bacteria is Azotobacter.

Example of symbiotic nitrogen-fixing bacteria - Rhizobium - Present in the root nodules of legumes

2. Nitrogen Assimilation

It is the process of formation of organic nitrogen compounds such as aminoacids, chlorophyll etc from inorganic nitrogen compounds.

Plants absorb nitrogen from the soil in the form of nitrate or ammonium

Nitrate ions absorbed is reduced to nitrite ions and then converted to ammonium ions and forms a major constituent in amino acids, nucleic acids, and chlorophyll.

In legume plants, with the symbiotic association of Rhizobium, nitrogen is directly absorbed as ammonium ions.

3. Ammonification

It is the procees in which organic nitrogen is converted back to ammonium.

It happens when a plant or animal dies, the organic nitrogen is decomposed back to ammonium by bacteria or fungi.

4. Nitrification

Nitrification is the process of conversion of ammonium ions to nitrate by the help of nitrifying bacteria. It has two main steps.

i) Conversion of ammonium ions to nitrite by Nitrosomonas bacteria

ii) Conversion of nitrite to nitrate by Nitrobacter bacteria

5. Denitrification

It is the process of reduction of nitrates back to nitrogen gas.

Bacterias like Clostridium and Pseudomonas under anaerobic condition converts nitrate back to nitrogen molecule and completes the nitrogen cycle.