NEET 2025 Zoology Question 150 Solution

In ecosystem energetics, production and productivity represent related but dimensionally distinct quantities:

• • Primary Production: The total quantity of organic matter or biomass produced per unit area during photosynthesis over an arbitrary period. Expressed in terms of biomass weight ($g/m^2$ or $g \cdot m^{-2}$) or energy content ($kcal/m^2$ or $kcal \cdot m^{-2}$).
• • Productivity: The rate at which biomass is generated per unit area per unit time. Because it is a rate, it must incorporate a time dimension (typically per year, $yr^{-1}$).

Evaluating the mathematical dimensions:

• • In terms of biomass: $(g \cdot m^{-2}) \cdot yr^{-1}$.
• • In terms of energy content: $(kcal \cdot m^{-2}) \cdot yr^{-1}$.
• • This standardized unit enables rigorous comparison of biological conversion efficiencies across diverse biomes (e.g. coral reefs vs tropical rainforests vs deserts).

Reviewing the provided choices:

• • Option (1) $g \cdot m^{-2}$: Unit of production, lacks time dimension.
• • Option (2) $kcal \cdot m^{-2}$: Unit of production, lacks time dimension.
• • Option (3) $kcal \cdot m^{-3}$: Energy per unit volume, inappropriate for aerial/surface ecosystem productivity.
• • Option (4) $(kcal \cdot m^{-2}) \cdot yr^{-1}$: True rate unit containing energy, area, and time dimensions.

The unit of productivity of an ecosystem is $(KCal \cdot m^{-2})yr^{-1}$, which is Option (4).