Which Is True About Mediated Transport Across Cell Membranes

Multiple Choice

Which is true about mediated transport across cell membranes?

A) It refers to the movement of ions through protein channels.
B) It refers both to simple diffusion and to the active transport of molecules.
C) It is characterized by saturable carriers and a maximum velocity of transport.
D) As the concentration gradient across a membrane increases,the transport rate always increases.
E) It is nonspecific;any transporter can transport any molecule across the cell membrane.