Final answer:
A protein pump in biology, such as the sodium-potassium pump, uses energy to actively transport ions across the cell membrane against concentration gradients.
Step-by-step explanation:
The correct sentence for a protein pump in biology is: "The protein pump actively transports ions across the cell membrane." This process of active transport requires energy in the form of ATP to move substances such as ions and molecules against their concentration gradients, which means from an area of low concentration to an area of high concentration. Protein pumps like the sodium-potassium pump exchange sodium ions for potassium ions across the plasma membrane of animal cells, a critical function for the operation of nerve cells and maintaining cellular homeostasis.