In cells, membrane proteins are responsible for the passage of substances that can't cross the membrane on their own. Channels and transporters are involved in facilitated diffusion. Pumps are involved in active transport. In terms of their properties or functions, which statement most accurately describes how these three types of membrane proteins compare?
a) Among the three types, only pumps are thought to undergo a shape change as part of their function.
b) Pumps are selective; channels and transporters are not selective.
c) Channels and transporters are integral membrane proteins; pumps are peripheral membrane proteins.
d) Among the three types, only pumps can concentrate substances on one side of the membrane.