Question

two molecules that can cross a lipid bilayer without help from membrane proteins are O2 and CO2, what property allows this to occur

Answer 1

O2 and CO2 are both nonpolar molecules that can easily pass through the hydrophobic interior of a membrane! Hope it helps

Answer 2

both the molecules are too small and have no charge therefore they can move across a membrane via gradient pressure from higher concentration to lower via simple diffusion. they don't need any atp or energy.