Comprehension:
An ecosystem is a structural and functional unit of nature, which comprises of both abiotic (e.g., air, water, soil) and biotic (e.g., producers, consumers, decomposers) components. Productivity, decomposition, energy flow and nutrient cycling are four key important processes in an ecosystem. Primary productivity is rate of capture of solar energy or biomass production by producers. The energy flow is unidirectional and plants can utilize only 1% of available solar energy and energy is transferred among trophic level, following 10% law. The rate of capture of solar energy or total production of biomass by producers is called as gross primary productivity. The energy left after utilisation by producers is called as net primary productivity. Rate of assimilation of food energy by the consumers is referred as secondary productivity. Decomposition processes such as fragmentation of detritus, leaching and catabolism are responsible for converting detritus into CO2, H2O and inorganic nutrients.
Given that NPP is Net Primary Productivity, GPP is gross primary productivity, R is respiration and SP is secondary productivity, choose the correct relationship.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → GPP = NPP + R
Gross primary productivity is the total rate at which producers capture solar energy and fix biomass. Part of it is spent by the plants themselves in respiration (R), and what is left over — the passage calls it “the energy left after utilisation by producers” — is the net primary productivity (NPP).
So NPP = GPP − R, which rearranges to GPP = NPP + R. Secondary productivity belongs to the consumers and does not enter this relation at all.