Question

Why is diffusion insufficient to meet the oxygen demand of multicellular organism?

Answer 1

in multicellular organisms

all the cells may not be in direct contact with the sorrounding environment

. thus simple diffusion will not meet the requirements of all cells

Answer 2

In multi cellular organisms , especially humans there are numerous number of cells.

The oxygen requirements of an animal cannot be met by the process of diffusion as it is a very slow process. To overcome this, multicellular organisms have specialized cells and tissues for performing various necessary functions of the body such as intake of oxygen and food.