Nitrogen Cycle: Definition, Stages & Significance

Nitrogen Cycle is a biogeochemical process that converts nitrogen into many types of compounds consecutively passing from the atmosphere to soil to living organisms and back into the atmosphere. Nitrogen is considered to be the most important constituent of amino acids, proteins, hormones and chlorophylls which are the building block of living organisms on earth. Nitrogen cycle makes nitrogen available to living organisms and the balance of nitrogen is maintained in the atmosphere through Nitrogen Cycle.

The stages of Nitrogen Cycles comprise Nitrogen fixation, Nitrification, Assimilation, Ammonification and Denitrification. Students learn the process of the Nitrogen Cycle in their primary school. You can check NCERT Solutions for Class 8 Science Chapter 2 for a better understanding of the concept. We have provided detailed information on Nitrogen Cycle in this article. Read on to find out about its definition, stages and importance.

Nitrogen Cycle: Definition

The Nitrogen Cycle is a process by which nitrogen is converted into different chemical compounds. The conversion is carried out through biological and chemical processes. Nitrogen Cycle transforms nitrogen from one form to another. Nitrogen is abundantly available in the atmosphere but it is not in usable form. Nitrogen Cycle converts atmospheric nitrogen into a usable form for the living organism.

Nitrogen Cycle involves various stages which include Nitrogen fixation, Nitrification, Assimilation, Ammonification and Denitrification. The stages of the Nitrogen Cycle is covered in detail in the next section.

Stages of Nitrogen Cycle

Nitrogen Cycle is a multi-stage process where Nitrogen from the atmosphere is absorbed in the soil through the Nitrogen Fixation process, which is then converted into some usable compound by microbes and are assimilated into the food web by primary producers. When a living organism dies again microbes convert nitrogenous compounds into elemental nitrogen and complete the Nitrogen Cycle.

Nitrogen Fixation

It is the first step of Nitrogen Cycle, in which the atmospheric nitrogen which is in inert form is converted to a more usable form, Ammonia (NH3). The process of nitrogen fixation may take place through natural processes or also through man-made processes.

Types of Nitrogen Fixation

1. Atmospheric Nitrogen Fixation: This phenomenon occurs when energy of lightening breaks the nitrogen into nitrogen oxides and then the oxides are brought down to earth through rain water.
2. Industrial Nitrogen Fixation: This is a man made process where nitrogen gas is converted into ammonia through industrial process by combining Nitrogen with Hydrogen.
3. Biological Nitrogen Fixation: Conversion of nitrogen to ammonia with the help of living organisms are called as Biological Nitrogen Fixation. To carry out the conversion, nitrogenase enzyme is used. Some of the examples of nitrogen fixing aerobic microbes are Azotobacter and Beijerinckia while, the anaerobic microbes are Rhodospirillum.

Nitrification

The process of converting ammonia into nitrate in presence of bacteria is called nitrification. Therefore, nitrites are formed with the help of Nitrosomonas bacterium species by oxidation of ammonia. It is later converted into nitrates by Nitrobacter. The reaction of conversion is as follows:

2NH₄⁺ + 3O₂ → 2NO₂^– + 4H⁺ + 2H₂O

2NO₂^– + O₂ → 2NO₃^–

Assimilation

Ammonia, nitrite ions, nitrate ions or ammonium ions present in the soil after Nitrogen Fixation and Nitrification are absorbed by roots of plants to form plant proteins. These are then transferred to the other living organism through the food web. This entire process of transfer of Nitrogen from soil to a living organism is called assimilation.

Ammonification

The process of decomposition of organic matter of dead plants and animals by microorganisms to produce ammonia is called ammonification. This process produces ammonia and ammonium. The ammonia produced is further used in the biological process.

Denitrification

The process of reduction of nitrates into nitrogen gas is called denitrification. This is carried by bacterial species such as Pseudomonas and Paracoccus in the absence of oxygen. It is the final stage of Nitrogen Cycle where inert form of Nitrogen goes back to the atmosphere, thereby completing the Nitrogen Cycle.

Importance of Nitrogen Cycle

Some of the benefits of the Nitrogen Cycle are as follows:

1. It helps in synthesis of chlorophyll for the plants which is necessary for the process of photosynthesis.
2. It converts nitrogen gas into useful compounds necessary for the plant growth.
3. Nitrites and nitrates are important compounds used for the cultivation of plants are made available through Nitrogen Cycle.
4. The balance of Nitrogen in the ecosystem is maintained through the Nitrogen Cycle.

FAQs Regarding Nitrogen Cycle

The frequently asked questions on the Nitrogen Cycle are given below:

Q. What is Denitrification?
A. The process of reduction of nitrates into nitrogen gas is called denitrification

Q. What is the nitrogen cycle?
A. Nitrogen Cycle is a biogeochemical process in which nitrogen is converted into many types of compounds consecutively passing from the atmosphere to soil to living organisms and back into the atmosphere.

Q. What is Nitrogen fixation?
A. The conversion of nitrogen into ammonia through a natural or man-made process is called Nitrogen Fixation.

Q. What are the stages of the nitrogen cycle?
A. The stages of the Nitrogen Cycle includes Nitrogen fixation, Nitrification, Assimilation, Ammonification and Denitrification.

Through this article, we have provided you with detailed information on the Nitrogen cycle. You can solve the CBSE Class 8 practice questions on Embibe for Mathematics and Science. You can also take CBSE Class 8 mock tests for these subjects.

We hope this detailed article on Nitrogen Cycle helps you. If you have any questions, feel to ask in the comment section below and we will get back to you at the earliest.