Which pigment is present in the root nodules of legumes ?


Write the various natural methods involved in the replenishment of the soil fertility.

Natural methods involved in the replenishment of the soil ferility are :

(1)Weathering of rocks.

(2) Decomposition of fallen leaves, twigs, dead plants and animals and excreta and their convertion to humus.

(3)Biological nitrogen fixation.


Mention the artificial methods involved in the restoration of soil fertility.

Artificial methods That restore the fertility of soil are :

(1)By adding farm yard manure or animal excreta to the soil.

(2)By adding fertilizers, manure.

(3)By green manuring.

(4)By crop rotation.

(5)By controlling over-grazing.


Mention the significance and disdvantages of hydroponics.

Significance of hydroponics :

1. Through hydroponic gardening; plants can be grown anywhere as long as their growth requirements are met.

2.Plants produced are free from soil pathogens and diseases as no soil is involved.

3. Plants grown are free from harmful chemicals as fertilizers and pesticides are not used.

4.The plants can be produced at those places where there is scarcity of land and the soil is thin or infertile.

5. The plants grown by this method are more healthy.

Disadvantages of hydroponics :

1. The initial set-up is very costly.

2.It needs the help of expert scientists to prepare the required nutrient medium and its maintenance.


List the criteria for essentiality of elements.

Arnon and Stout gave the following criteria for the essentiality of elements :

1.The essential elements should be necessary for growth and reproduction of the plant. It should be indispensable. The plant should not be able to complete its lifecycle in the deficiency of the element.

2.The element should not be replaceable and its requirement should be specific. The deficiency of the element should not be met by supplying some other element.

3. There should be direct involvement of the element in the metabolism of the plant.


Give the role of minerals.

Role of minerals :

1. The mineral elements are absolutely necessary for supporting normal growth and reproduction.

2.The minerals are components of protoplasm.The elements having variable valency bring oxidation and reduction reactions e.g. Fe, Cu.

3.K+ions help in the opening and closing of stomata.

4.Salts of weak acids and weak bases act as buffers.

5.Minerals maintain osmotic potential of cell sap and permeability of plasmalemma.

6.Minerals also act as cofactors and thus bring catalytic reactions.

7.K+and boron help in transportation of food in the phloem tissue.