Suppose 2000 J of solar energy falls on green plants, and the producers fix only 1 per cent of it. The energy then passes from one trophic level to the next according to the 10 per cent law. Find the values of A, B and C in the figure.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A – 20 J, B – 2 J, C – 0.2 J
Plants fix only a small part of the sunlight that falls on them. After that, the 10 per cent law applies: only 10 per cent of the energy at one trophic level passes to the next.
- Producers (A) = 1 per cent of 2000 J = 20 J
- Herbivores (B) = 10 per cent of 20 J = 2 J
- Carnivores (C) = 10 per cent of 2 J = 0.2 J
Option (2) applies 10 per cent straight to the 2000 J of sunlight, which ignores the 1 per cent fixed by the producers. Options (3) and (4) start from 20 per cent and 2 per cent capture, which the question does not give.
NCERT Extract:
Energy Flow – “… Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR). We know that plants and photosynthetic bacteria (autotrophs), fix Sun’s radiant energy to make food from simple inorganic materials. Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world.”
Energy Flow – “… The number of trophic levels in the grazing food chain is restricted as the transfer of energy follows 10 per cent law – only 10 per cent of the energy is transferred to each trophic level from the lower trophic level.”