CBSE Class 10 Science 2022 · Paper 31/6/1 · Question 13

(a) Decomposers (bacteria and fungi) break down the complex organic substances of dead remains and wastes into simple inorganic substances that go into the soil and are used again by plants. Without them dead matter would pile up with its nutrients locked away, and the cycling of materials in the biosphere would break down. (b) The energy captured by producers passes to herbivores and then to carnivores but never comes back: it does not revert to the solar input, the energy passed to herbivores does not return to the producers, and at every level much of it is lost as heat that cannot be used again. So energy flows in one direction only. (c) Only about $10\%$ of the energy at one trophic level is passed on to the next (the 10 per cent law). The loss at each step is so great that very little usable energy remains after four trophic levels, so a food chain generally consists of only three or four steps.