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Class 10 Class 12
Describe the passive mineral absorption.

Passive mineral absorption : It is the absorption which occurs without expenditure of energy. It occurs by following methods :

(A) Diffusion (B) Mass flow

(A) Diffusion : It is the movement of minerals down the concentration gradient .

Types of Diffusion : It is of Two types as :

(a) Passive Diffusion : It occurs either by dissolving of minerals in matrix cell membrane or through pores. It is a physical process which needs no energy. Water, 02, C02, etc. diffuse by passive diffusion. Sodium in Nitella is absorbed by passive diffusion.

(b) Facilitated diffusion : It occurs by special protein molecules.

(B) Mass flow : Large amount of water is absorbed daily by the plant. Along with the water minerals from soil are absorbed into roots. More the rate of transpiration, more would be water absorption and thus more minerals pass into the roots and then ascend upwards into stem.

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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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Which pigment is present in the root nodules of legumes ?

Leghaemoglobin.
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Name the best known symbiotic nitrogen fixing bacterium.

Rhizobium.
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What type of condition is created by leghaemoglobin in the root modules of legumes ?

Anaerobic.
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