Read the following passage carefully and answer the given questions.
Productivity in the Ecosystem
The flow of energy through a terrestrial ecosystem starts with the harnessing of sunlight by autotrophs. The radiant energy is converted by photosynthesis to organic compounds is known as productivity. The productivity is expressed in units of energy per unit of area per unit time. The amount of organic matter present at any given time is biomass. The productivity of any ecosystem is affected by many parameters like weather conditions, nutrient availability etc. The productivity of any ecosystem does vary seasonally and yearly.
The Net Primary Productivity of an ecosystem are represented by:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → NPP = GPP - Respiration
Option (1) NPP = GPP + Respiration — Incorrect. Respiration uses up part of what plants make, so it must be subtracted, not added.
Option (2) NPP = GPP - Respiration — Correct. GPP is the total organic matter made in photosynthesis. Taking away what the plants burn in respiration leaves the net amount.
Option (3) NPP = Radiant Energy - GPP — Incorrect. Radiant energy minus GPP is the sunlight the plants did not capture, not their net production.
Option (4) NPP = Radiant Energy + GPP — Incorrect. Adding sunlight to production has no meaning; NPP is always less than GPP.
Note: A similar question was also asked in CUET (UG) 2025 on 22-05-2025 (Slot 2).
NCERT Extract:
Productivity – “… 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).
GPP – R = NPP
Net primary productivity is the available biomass for the consumption to heterotrophs (herbiviores and decomposers).”