Q27 of 50 Page 1

(i) What is the primary productivity? Why does it vary in different types of eco-systems?

(ii) State the relation between gross and net primary productivity.


(i)


• The rate of biomass production per unit area is called productivity. The primary productivity of a community is the rate at which biomass produced per unit area by plants, the primary producers.


• The term primary indicates that we are concerned with the first tropic level in the system.


• Primary productivity vary with different type of eco-system because primary productivity depends upon the number and types of producers occurring in it and the environmental conditions in the area. Thus every ecosystem have different primary productivity.


(ii)


• The total fixation of energy by photosynthesis is referred to as gross primary productivity (GPP).


• The proportion which remains after respiration losses in the plant is termed net primary productivity (NPP).


• Thus the difference GPP and respiration is known as net primary productivity.


• NPP represents the actual rate of production of new biomass that is available for consumption by hetrotropic organisms.


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