In an ecosystem the energy flow is always unidirectional.

Explanation

(1) For considering the energy flow in an ecosystem the following aspects have to be taken into account :
(i) The efficiency of the producers in the absorption and conversion of the solar energy.
(ii) The quantity of converted energy is used by the consumers.
(iii) The total input of energy in the form of food and its efficiency of assimilation by the consumers.
(iv) The amount of energy is lost through respiration, heat, excretion,etc. and the ultimate GNP or gross net production.
(2) The energy captured by autotrophs never returns back to the solar energy. The energy obtained by the berbivores will never go back to autotrophs. Hence energy flow is always unidirectional.
(3) The energy flow through different trophic levels is progressive and hence previous trophic level cannot get this back.
(4) The amount of energy keeps on decreasing as it travels to further trophic level. This loss of energy is due to dissipation at heat formed during various metabolic activities of the organism. The energy loss is measured as respiration coupled with unutilized energy.
(5) If the food chain is shorter there is greater amount of available food energy. When the length of food chain increases, there is corresponding more loss of energy.