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 amount of organic matter accumulated in an ecosystem at a given time is known as-
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Standing crop
Option (1) Standing state — Incorrect. Standing state is the amount of nutrients, such as carbon, nitrogen, phosphorus and calcium, present in the soil at a given time. The term is from the pre-rationalised NCERT. It is about nutrients, not the organic matter of living things.
Option (2) Standing crop — Correct. It is the living material present at one moment in a trophic level. It is an amount, not a rate.
Option (3) Standing biomass — Incorrect. Biomass is the measure in which the standing crop is expressed, as fresh or dry weight. “Standing biomass” is not the book’s name for the amount itself.
Option (4) Standing productivity — Incorrect. Productivity is a rate: the organic matter made per unit area per unit time. An amount present at one moment cannot be a rate, and there is no such term.
Note: One can argue for Option (3) Standing biomass, because the passage says that the amount of organic matter present at any given time is biomass. The book’s term for this amount is standing crop, which is measured as biomass, so Option (2) is the better answer.
NCERT Extract:
Energy Flow – “… Organisms at each trophic level depend on those at the lower trophic level for their energy demands. Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area. The biomass of a species is expressed in terms of fresh or dry weight. Measurement of biomass in terms of dry weight is more accurate.”