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 unit for expressing productivity is -
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (Kcal m-2) yr-1
Productivity is a rate: the organic matter (or energy) produced per unit area per unit time. So its unit needs area (m-2) and time (yr-1) once each.
Option (1) (Kcal m-2) yr-1 — Correct. Energy per square metre per year.
Option (2) (Kcal m-2) yr-2 — Incorrect. yr-2 would mean per year per year, a rate of change of productivity.
Option (3) (Kcal m-1) yr-1 — Incorrect. m-1 is per metre of length, not per unit area.
Option (4) (Kcal m2) yr-1 — Incorrect. m2 multiplies by area instead of dividing by it.
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.”