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Class 10 Class 12
Nitrogen is an essential element for plants and is found in abundance as atmospheric nitrogen. But most plants are unable to use it. Why is it so and in what form do plants utilise nitrogen?

Most plants cannot utilise the atmospheric nitrogen as it is almost inert in nature. Nitrogen combines with oxygen by atmospheric activities and is brought down by rain to the soil. Highly specialised organisms called nitrogen fixers, occur in the soil and they convert nitrogen into nitrates or nitrites or a reduced cationic form like ammonium. These compounds enter the plants as nutrients in the form of dissolved nitrites and nitrates through the root and are assimilated as organic nitrogen.
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What type of condition is created by leghaemoglobin in the root modules of legumes ?

Anaerobic.
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Name the best known symbiotic nitrogen fixing bacterium.

Rhizobium.
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Which pigment is present in the root nodules of legumes ?

Leghaemoglobin.
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How is nitrogenase enzyme protected ?

The nitrogenase enzyme is very sensitive to the molecular oxygen. It requires anaerobic conditions to work. The leg-haemoglobin in the nodule acts as an oxygen scavenger just meainting the anaerobic condition needed by the enzyme.
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What is Hidden hunger in the case of plants?

Hidden hunger refers to a situation in which a crop needs more of a given nutrient yet has shown no deficiency symptoms. The nutrient content is above the deficiency symptom zone but still considerably needed for optimum crop production
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