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

 

Diffusion is insufficient to meet the oxygen requirements of multicellular organisms like humans because it is not an efficient way to move oxygen molecules from the atmosphere to cells.

The surface area to volume ratio of cells decreases as organisms get bigger. This means that there is less surface area available for diffusion to occur. Multicellular organisms also have circulatory systems, which help to move oxygen molecules around the body. Diffusion alone is not enough to meet the oxygen requirements of multicellular organisms because they are too big and have too few surface area for efficient diffusion to occur.