Explain the 'ten percent law' for the flow, of energy, through a food chain.
Why do we say that the flow of energy through the food chains is unidirectional ?

Explanation

According to the ten percent law, `90%` of the energy from the previous trophic level is lost as heat to the environment. Only `10%` of the energy in the form of food energy, present within the first trophic level flows ot the second trophic level and in the same way from second trophic level to the third level and so on.
The energy, in the form of food always from first trophic level to the last trophic level of a food chain. It never flows back from the last trophic level to the last trophic of a food chain. It never flows back from the last trophic level to the first trophic level, so we say that the flow of energy is unidirectional through the food chains.