Every ecologist knows flow of energy is unidirectional in an ecosystem , I tried to find its reason but didn't find any reasonable one so please help me .

It is based on the very definition. Generally speaking, it refers to the energy flow through a food chain. During each step of consumption energy is obviously lost and there is no way that you can "unconsume" something.

I think you can get some sort of "cycling" going on in the short term.

For example, cats eat rats, but rats will eat a dead cat if they find one.

In general the path is pretty much unidirectional.

Edited December 18, 201312 yr by John Cuthber

The energy flow is usually used in the context of energy loss during each step of the flow. I.e. the directionality does not refer to the cyclic nature of ecosystems (in which microorganisms can play multiple roles, for example), but rather to the steps of biomass consumption

As such a given species can be at different levels depending on how the food chain is built. That, in turn depends on the aspects and details of a given ecosystem one tries to describe.

 

Cycling is usually discussed in relation to material but not to energy (i.e. energy flow) as energy is obviously not recycled, but gradually lost at each step as heat (however the food web is structured).

I think you can get some sort of "cycling" going on in the short term.

For example, cats eat rats, but rats will eat a dead cat if they find one.

In general the path is pretty much unidirectional.

that's what I want to say in a food chain cat come on next tropic level to cat ie a cat eats a rat but what if a rat eat a cat then in this case energy is flowed back word then is the rule voilated

that's what I want to say in a food chain cat come on next tropic level to cat ie a cat eats a rat but what if a rat eat a cat then in this case energy is flowed back word then is the rule voilated

But in reality there is no food chain. It's more of a crazy web. The chain is tropic levels as Charony has said. It doesn't matter what is eating what, the energy gained from consuming something is less than the total energy of whatever was consumed. So there is a net energy loss.

It follows the 2nd law of thermodynamics (and the 1st law). As energy passes from one organism to another energy is transformed into free energy and heat. Free energy can be used by the organism in metabolic processes. Heat escapes the organism/system, and thus the entropy of the universe increases, as it always must. Therefore, the total free energy into a system (organism) is always more than what comes out.

Why more energy flows through detritus food chain than grazing food chain

Plant matter goes largely uneaten and grazers along with everything up from them produces waste. All of this becomes part of the detritus food chain.