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

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

Right Option : C
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Question : 2

Which of the following are correct :

(a) The root nodules of certain leguminous plants like peas and beans have nitrogen-fixing bacteria.

(b) Some non leguminous plants like Ginkgo can also fix atmospheric nitrogen.

(c) Nitrogen present in the atmosphere can be absorbed directly by most plants and animals.

Right Option : A
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Question : 3

Which of the following are correct :

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

(b) The nitrates get stored in the soil and the atmospheric nitrogen is fixed.

(c)  Nitrogen present in the atmosphere cannot be absorbed directly by most plants and animals.

Right Option : D
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