Why is there less biomass higher up on the pyramid? why can't there be an equal amount of organisms at each trophic level?

There is less biomass in the higher up on the pyramid due to the utilization of energy by the organisms from the second tropic level  because the in the first tropic level green plants or producers are present.

Explanation:

During the transfer of biomass from one tropic level to the next one most of them(biomass) are utilized by the organism of the upper tropic level.

        As a result amount of biomass decreases as the energy flows from one tropic level to the next one.

       There cannot be equal amount of organism at each tropic level because if the same thing happens then the flow of energy cannot be possible to the upper most topic level as every organism of each tropic level will eat the organism of it"s lower tropic level and biomass will be consumed in high rate in second and third tropic levels.Finally there will be no biomass left to be transferred to the fourth or the upper most tropic level.This will hamper the normal energy flow.

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