Question #984b2

1 Answer
Nov 25, 2017

CO_2 and O_2 are both small, nonpolar, non-charged molecules.

Explanation:

Substances that can cross the cell membrane by passive diffusion need to be small, nonpolar, and non-charged substances.

CO_2 and O_2 fit this description perfectly and thus can cross the cell membrane by passive diffusion.

This is very efficient because O_2 constantly has to get into the cell and CO_2 has to get out.

If the cell had to expend energy in transporting these molecules, it would have to use a TON of energy that it wouldn't have.