Question

Why diffusion is not sufficient for organisms like humans?

Answer 1

Heya....

The oxygen requirements of humans or other multicellular organisms can't be meet by the process of diffusion because diffusion is a very slow process....And humans are needed to meet with oxygen fastly....

So we need to make direct contact to get oxygen with nature...

Answer 2

evey organism enhale oxygen for surviving and thus the process of diffusion take place very slowly and living organism need oxygen fastly thus we have to maintain a direct contact with nature