Net Primary Production (NPP):
1. It is the amount of organic matter stored by producers per unit area.
2. NPP is equal to organic matter synthesized by photosynthesis (-) minus the rate of respiration.
Gross Primary Production:
1. It is the amount of organic matter synthesized by producers per unit time and area.
2. GPP is equal to rate of increase in body weight of producers plus loss suffered through respiration.