The sodium-potassium pump is a membrane protein that pumps sodium out of the cell and brings potassium in. It does this against the concentration gradients; in other words, it pushes both molecules from areas of low concentration to areas of already high concentration. What type of transport is this? a. passive transport, which requires energy
b. passive transport, which does not require energy
c. active transport, which requires energy
d. active transport, which does not require energy