Question #984b2

1 Answer
Nov 25, 2017

Answer:

#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.