(a) The existence of decomposers is essential in a biosphere because they breakdown complex organic substances into simple inorganic substances that can be absorbed by the plants. Thus, decomposers:
* replenish the soil naturally
* helps in removing 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 (i.e., autotrophs) and the energy captured by the autotrophs does not go back to the solar input.
Hence, the flow of energy is unidirectional.
