Please explain the Nitrogen cycle as per NCERT Science textbook in simple language.

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In the atmosphere, the concentration of nitrogen is about 78%. It is essential for plants. Nitrogen forms a structural component of many important molecules such as DNA, RNA, and other vitamins.

Plants cannot absorb nitrogen from the atmosphere. So, how is atmospheric nitrogen utilized by plants?

There are methods that change atmospheric nitrogen into usable forms through the process of nitrogen fixation. Two such methods are given below.

[1]. During lightning and thunder, the high temperature and pressure in the air convert atmospheric nitrogen into oxides of nitrogen that can dissolve in water to produce nitric and nitrous acids. These fall along with rain.

[2]. Certain forms of bacteria are able to convert atmospheric nitrogen into usable forms such as nitrates and nitrites. Such nitrogen fixing bacteria are commonly found in the roots of legumes (plants of pulses) inside special structures called root nodules.

These usable forms of nitrogen are absorbed by plants to produce many compounds such as amino acids, which in turn form proteins.

When an animal feeds on plants, nitrogen enters its body.

How does nitrogen return to the environment?

When plants and animals die, they start decomposing after some time. During this process, proteins are converted into nitrates and nitrites by the action of decomposing bacteria. Certain other forms of bacteria convert nitrates and nitrites into elemental nitrogen. Thus, nitrogen flows between the various components of the biosphere in a cyclical manner.