What is the term used to denote the total rate of organic matter production during photosynthesis in an ecosystem?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Gross primary productivity
Productivity is the rate at which biomass is produced. The total rate at which plants make organic matter by photosynthesis is the gross primary productivity (GPP). Plants use part of it in respiration (R). What is left, GPP − R, is the net primary productivity (NPP).
Option (1) Secondary productivity — Incorrect. Secondary productivity is the rate at which consumers form new organic matter. It is not production by photosynthesis.
Option (2) Net productivity — Incorrect. ‘Net’ means after losses have been taken away. The question asks for the total rate, before respiration is subtracted.
Option (3) Net primary productivity — Incorrect. Net primary productivity is GPP minus respiration losses. It is the biomass left for herbivores and decomposers, not the total.
Option (4) Gross primary productivity — Correct. Gross primary productivity is the rate of production of organic matter during photosynthesis, the total made by the producers.
NCERT Extract:
Productivity – “… It can be divided into gross primary productivity (GPP) and net primary productivity (NPP). Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). … Secondary productivity is defined as the rate of formation of new organic matter by consumers.”