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 concentration difference of the molecule across the membrane increases. This is the case because

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