(a) The existence of decomposers is essential in a biosphere because they breakdown complex organic substances into simple inorganic substance that can be absorbed by the plants. Thus, decomposers:
(i) Replenish the soil naturally.
(ii) Helps in reusing the biodegradable waste.
(b) In a food chain the energy moves progressively through the various trophic levels, it is no longer available to the previous level and the energy trapped by the autotropes does not flows back. Thus flow of energy is unidirectional.