(i) What is primary productivity? Why does it vary in different types of ecosystems?
(ii) State the relation between gross and net primary productivity.

(i) The amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis is called primary production.

The primary productivity depends on different plant species present in a given ecosystem and each of their photosynthetic efficiency. Also, the environmental factors, availability of various nutrients vary in different ecosystems, leading to variations in primary productivity.

(ii) Gross primary production of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilized by the plants in respiration.

Net primary productivity or NPP is the gross primary productivity minus the respiratory losses (R).
GPP - R = NPP