Question

Why is it impossible to understand the totality of the interactions among the organisms in the biosphere?

Answer 1

In order to understand the totality of the interactions among the organisms in the biosphere, we need to at least understand how the all genes function within organisms and interact with others organism and environment around it.
If we try to make this effort in a world where organisms will keep evolving and environment will keep changing like us, that tasks is impossible to finish.