Read the following and choose the option with all the correct statements.

(i) Ecosystem is a functional unit of nature and comprises abiotic and biotic components.

(ii) Vertical distribution of different of different species occupying different levels is called stratification. In forests, trees occupy top vertical part, herbs the second and shrubs and grasses occupy the bottom layer.

(iii) There is unidirectional movement of energy.

(iv) Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (g -2 ) or energy (kcal m -2 ).

(v) The rate of biomass production is called productivity. It is expressed in terms of g -2 yr -1 or kcal m -2 yr -1 .

(vi) Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis.

(vii) Gross primary productivity minus respiration losses (R) is the net primary productivity (NPP).

(viii) Secondary productivity is defened as the rate of formation of new organic matter by producers.

(ix) The annual net primary productivity of whole biosphere is approximately 115 billion tons of organic matter.

(x) The important steps in the process of decomposition are fragmentation, leaching catabolism, humification and mineralization.

(xi) By the process of leaching, water-insoluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.

(xii) Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and increases fertility of soil.