Question

Question 1
Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?

Answer 1

Unlike the unicellular organisms, the multi-cellular organisms have complex body structures with specialised cells and tissues to perform various necessary functions of the body. There are more than 1 trillion cells in the human body, most of which are deep-seated without any in direct contact with the surrounding environment. Clearly, simple diffusion cannot meet the oxygen requirement of all these cells.