The rate of biomass production is called productivity and it is expressed as:
(A) \( \mathrm{g\,m^{-2}\,yr^{-1}} \)
(B) \( \mathrm{(kcal\,m^{-2})\,yr^{-1}} \)
(C) \( \mathrm{g\,m^{-1}\,yr^{-1}} \)
(D) \( \mathrm{(kcal\,m^{-1})\,yr^{-2}} \)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) and (B) only
Productivity is the rate of biomass production. Biomass is measured per unit area, as weight (g m-2) or as energy (kcal m-2), and the rate is taken per year. So the unit has m-2 and yr-1.
(A) \( \mathrm{g\,m^{-2}\,yr^{-1}} \) — Correct. Weight of biomass per square metre per year.
(B) \( \mathrm{(kcal\,m^{-2})\,yr^{-1}} \) — Correct. Energy in the biomass per square metre per year. This is the unit used to compare the productivity of different ecosystems.
(C) \( \mathrm{g\,m^{-1}\,yr^{-1}} \) — Incorrect. This is per metre of length, not per unit area.
(D) \( \mathrm{(kcal\,m^{-1})\,yr^{-2}} \) — Incorrect. It has two faults: per metre instead of per square metre, and per year squared instead of per year.
Note: A similar question was also asked in CUET (UG) 2025 on 02-06-2025 (Slot 2) and on 15-05-2025 (Slot 2).
NCERT Extract:
Productivity – “A constant input of solar energy is the basic requirement for any ecosystem to function and sustain. Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (g m–2) or energy (kcal m–2). The rate of biomass production is called productivity. It is expressed in terms of gm–2 yr –1 or (kcal m–2) yr–1 to compare the productivity of different ecosystems.”