Which is True About Mediated Transport Across Cell Membranes

Question

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.

Accepted Answer

Mediated transport involves the movement of molecules or ions with the help of specific carrier proteins or channels. It has saturable carriers, which means that at higher concentrations of the molecule being transported, the rate of transport will not increase further because all carriers become occupied. The maximum velocity of transport is limited by the number of available carriers, hence, the term "saturation".