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 biomass available for consumption by herbivores and decomposers is known as-
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Net Primary Productivity
Option (1) Gross Primary Productivity — Incorrect. GPP is the total made in photosynthesis. Part of it is used by the plants in respiration, so not all of it is available to others.
Option (2) Net Primary Productivity — Correct. NPP is what remains after the plants’ own respiration, and it is this that herbivores and decomposers can use.
Option (3) Secondary Productivity — Incorrect. Secondary productivity is the rate at which consumers form new organic matter. It is made from the food they eat, not the food available to them.
Option (4) Standing Biomass — Incorrect. This names an amount present at one moment; the book calls it the standing crop. It is not a rate of production.
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).”