Question

Why is the nitrogen cycle called a perfect cycle?

Answer 1

There are various biogeochemical cycles present. The nitrogen cycle is one such cycle in which the nitrogen is converted into various chemical forms and is circulated in the atmosphere, Land and marine systems. The atmospheric nitrogen is present in the molecular form which needs to be converted into utilisable form.

Complete answer:
The atmosphere contains around 78% of the nitrogen present in the molecular form which cannot be utilised by the living beings. The living beings need nitrogen for their growth and development. It is the main component of DNA, RNA and proteins. So the living organisms need it to the maximum. The nitrogen cycle helps in conversion of the atmospheric nitrogen to the utilisable form in the living beings and then circulating back into the atmosphere. The nitrogen cycle involves fixation, ammonification, nitrification and denitrification.

Let us discuss the steps of nitrogen cycle.
Fixation- In this step the atmospheric nitrogen is converted into the utilisable form like nitrates, nitrites by the process of lightening or also by the bacteria. The Rhizobium bacteria present in the root nodules of the leguminous plants convert free nitrogen to nitrates, nitrites and ammonium salts. This is assimilated by the living beings for carrying out their metabolic activities.

Ammonification- The decomposition of plants and animals release nitrogen in the form of organic nitrogen. The bacteria and fungi converts it into ammonia. This is carried out by ammonifying bacteria. This process of known as ammonification.

Nitrification- The ammonia is toxic for the living beings. The nitrifying bacteria like Nitrobacter, Nitrosomonas converts the ammonia into nitrates. These bacteria are present in the soil.

Denitrification- The bacterial species like Psudococcus converts the nitrates in the soil to free atmospheric nitrogen. This conversion takes place at the anaerobic conditions.

In the nitrogen cycle, the microorganisms collectively work to cycle the nitrogen in the atmosphere as well as in the living beings. This conversion is carried out by both the biological and physical components of the ecosystem. Thus, we can say that the nitrogen cycle is a perfect cycle.

Note: The nitrogen in the soil is absorbed by the growth and development of the plants. As a result of which the soil gets depleted of nitrogen. The use of fertilisers rich in nitrogen helps in replenishing the nitrogen. The leguminous plants also improve soil fertility as the nitrogen-fixing bacteria house in their root nodules.