Question

Which statement explains why oxygen molecules easily diffuse across a cell membrane while protein molecules do not?

A. Protein molecules form membrane channels that oxygen molecules can pass through.
B. Oxygen gas exists as molecules, but proteins are either liquids or solids.
C. Oxygen molecules fit between fatty acids, but protein molecules are too big.
D. Proteins contain oxygen that is more useful inside a cell than outside the cell.

Answer 1

C. Oxygen molecules are small (like CO2) and are able to diffuse across semipermeable membranes. Proteins are too big, and cannot get past them.

Answer 2

I believe C is the answer.