Question

select all that apply
which three of the following substances cross a membrane by passive diffusion?

carbon dioxide
oxygen
sugars
water
amino acids

Explanation:

Passive diffusion is the movement of substances across a membrane without energy input, down a concentration gradient. Small, non - polar or uncharged polar molecules can pass. Carbon dioxide ($\ce{CO_2}$) is a small non - polar gas, oxygen ($\ce{O_2}$) is a small non - polar gas, and water ($\ce{H_2O}$) is a small polar molecule that can pass via osmosis (a type of passive diffusion). Sugars are large polar molecules and amino acids are charged/polar and large, so they need active transport or facilitated diffusion (not passive diffusion).

Answer:

Carbon dioxide, Oxygen, Water