Rate of production of organic matter by producers per unit time and area is

In an ecosystem,the rate of production of organic matter during photosynthesis is termed as:

Justify the following statement in terms of ecosystem dynamics: "Nature tends to increase the gross primary productivity, while man tends to increase the net primary productivity".

Secondary productivity is the rate of formation of new organic matter by:

Assertion : Net primary productivity is gross primary productivity minus respiration.
Reason : Secondary productivity is produced by heterotrophs.

Explain productivity and its types.