A level biology surface area

Hey, in gas exchange, the surface area is reffering to of one cell or to all the skin that makes up an organism (size) ?
If it refers to cell, do all species have different size of cells?
And if insects and fish have low SA:V why do they need a special gas excuabge system rather than gasses just diffusing across their skin.
Thanks.

Reply 1

Illumilottie

Original post by Tanyme

It’s the surface area to volume ratio of the organism so the total surface area of all cells compared to the total volume of the organism.
they have a low surface area to volume ratio which means that the diffusion distance is longer so simple diffusion across the skin is not sufficient.