Question

what will happen if we kill all the organisms in one trophic Level

Answer 1

Answer: If we kill all the organisms in one trophic level, then transfer of energy as well as matter to next higherlevel will stop. It will lead to over- population at one particular levelcausing amongst the individuals. Thiswould seriously disturb the food chain and can cause the collapse of anecosystem even.
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Answer 2

Organisms in a particular trophic level of the food chain are inter-dependent and inter-related. Upon disturbing the organisms of one trophic level, the organisms dependent on these organisms in turn will be affected. So there will be  certain disbalance in the food chain. This will disturb the ecosystem and the food chain cannot be sustained.