Question

why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?

Answer 1

Unlike the unicellular organisms, the multicellular organisms have complex body structure with specialized cells and tissues to perform various necessary functions of the body. Since these cells are not in direct contact with surrounding environment so, simple diffusion cannot meet the oxygen requirement of all these cells.

HOPE it helps!!!!✌️✌️✌️

Answer 2

In multicellular organisms like humans the organization is complex moreover the cell number is high so it takes a lot of time to diffuse through all the cells (almost 3 years)
Also the nature of cells is complex so it takes a lot of time✌️✌️