Answer 1

Productivity is the rate of production of biomass at any trophic level at any given interval of time.

Gross productivity: It is the rate of production of organic matter by green plants per unit time per unit area. In other words, it is the total amount of productivity. 

Net primary productivity: It is the difference between gross primary productivity and the loss due to respiration.

Secondary Productivity : It is rate of production or formation of new organic matter by consumers especially the consumers of the first order or herbivores.