Which of the following channels would not be expected to generate a change in voltage by movement of its substrate across the membrane where it is found?

(a) an aquaporin
(b) a sodium channel
(c) a calcium channel
(d) a proton channel

(a) an aquaporin  

Explanation:

An aquaporin is a water channel which forms a pore in  the cell membrane and facilitates the movement of water. Aquaporin is an integral membrane protein (permanently attached to the membrane) that enables the in and out flow of the water. This channel also prevents the passage of ions and other solutes, so it cannot change the voltage. There are four types of aquaporins, and they are mostly found in the kidney with the function of water reabsorption.