In Facilitated Diffusion, the Diffusion Rate of a Specific Molecule

Multiple Choice

In facilitated diffusion, the diffusion rate of a specific molecule across a membrane does not continue to increase as the molecule's concentration difference across the membrane increases beyond a certain point.The reason is that

A) facilitated diffusion requires the use of ATP.
B) as the concentration difference increases, molecules interfere with one another.
C) the carrier proteins become saturated.
D) the transport protein is a channel protein.
E) the diffusion constant depends on the concentration difference.