Active transport-To pump a solute across a membrane against its concentration gradient requires work.It allows a cell to maintain internal concentrations of small solutes that differ from its enviorment.For example, compared with its surroundings, an animal cell has a much higher concentration of potassium ions and a much lower concentration of sodium ions. The plasma membrane helps maintain these steep gradients by pumping sodium out of the cell and potassium into the cell. ATP supplies the energy for most active transport. 1. Atp can power active transport is by transferring its terminal phosohate group directly to the transport protein. The protein can induce the protein to change its shape in a maner that translocates a solute bound to the protein across the membrane. EG. Sodium-potassium pump