Why diffusion is suficient in unicellular organisms but insufficient in multicellular organisms

Why diffusion is suficient in unicellular organisms but insufficient i

1.	Why diffusion is suficient in unicellular organisms but insufficient in multicellular organisms
Answer» In large multicellular organism like human,the oxyzen of air will have to travel large distance inside the human body to reach each and every cells of the body .Now,since diffusion is a very slow process it will take a very long time to make oxygen available to all the body cells.Thus diffusion is insufficient meet the oxygen requirement of multicellular because the volume of is so big that oxygen cannot diffuse into all the internal cell of human body quickly.HOPE ITS HELP