The flow of energy in an ecosystem is always unidirectional. It is said to be unidirectional because some energy is lost in form of heat when moving from one trophic level to the next for the maintenance of the homeostasis of an organism. As several trophic levels get intertwined, the energy flow doesn't follow a linear or a unidirectional pattern, rather it is multidirectional or we can say that as, in a food web, one organism takes place at different trophic levels in different food chain.