Question

Explain the following cycle in your own words with a suitable diagram.

Nitrogen cycle. 

Answer 1

Nitrogen cycle

The nitrogen cycle involves the conversion of nitrogen from its elemental form in the atmosphere into simpler molecules in the soil and water. These further get converted into more complex molecules in living beings. Finally, the complex molecules are reduced and released back into the atmosphere as simple nitrogen molecules.

Fixing atmospheric nitrogen involves the following steps:

1. Nitrogen fixation: It is the process wherein atmospheric nitrogen is converted into water-soluble nitrates. This step is performed by organisms like Rhizobium, Azotobacter and blue-green algae.
   \[\ce{N2 → NO3−  or NH4}\]
2. Nitrification: It is the process in which ammonia is first converted into nitrites and then into nitrates. This step is performed by nitrifying bacteria like Nitrosomonas and Nitrobacter.
   \[\ce{NH3 → NO2− → NO3−}\]
3. Assimilation: In this step, NH₃ and NO₃ are incorporated into the biological tissues.
4. Ammonification: It is the process in which complex, dead organic matter is decomposed into ammonia. This step is performed by organisms like decay bacteria and fungi.
   \[\ce{Organic nitrogen compounds → NH4+}\]
5. Denitrification: It is the process wherein the nitrates present in the soil are reduced to release nitrogen back into the atmosphere.
   \[\ce{NO3− → N2}\]