Nitrogen Fixation


 
 
Concept Explanation
 

Nitrogen Fixation

Nitrogen Fixation : 

Nitrogen present in the atmosphere cannot be absorbed directly by most plants and animals. It can be used only by a few simple organisms. The rest can use nitrogen only when it is converted into nitrates and nitrites. Certain microorganisms do this.

The process of converting free nitrogen of the atmosphere into compounds of nitrogen is called nitrogen fixation.

This is the process by which nitrogen of the nonliving world enters the living system. Nitrogen fixation occurs in three ways:

(i)  Atmospheric Fixation: The high temperatures and pressures produced during lightning allow nitrogen to combine with oxygen in the atmosphere to form oxides of nitrogen. These dissolve in rain water and get soaked into the soil, and form nitrates(NO_3).

N_2+O_2rightarrow 2NO

2NO+O_2rightarrow 2NO_2

4NO_2+O_2 +2H_2Orightarrow 4HNO_3

Nitric acid is carried by rain water to the soil where it forms nitrates. The nitrates get stored in the soil and the atmospheric nitrogen is fixed. The nitrates present in the soil are then absorbed by plants.

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Sample Questions
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Question : 1

Which of the following are correct :

(a) The fixation of nitrogen by some nitrogen-fixing bacteria is called biological nitrogen fixation.

(b) The process of converting free nitrogen of the atmosphere into compounds of nitrogen is called nitrogen fixation.

Right Option : C
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Question : 2

Nitrogen present in the atmosphere cannot be absorbed directly by most ___________________.

Right Option : C
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Question : 3

The high temperatures and pressures produced during lightning allow nitrogen to combine with _______________ in the atmosphere to form oxides of nitrogen.

Right Option : C
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