Active transport requires energy to move molecules against their concentration gradient. This process is essential for cells to maintain the proper concentrations of various ions and molecules necessary for their functioning.
In active transport, substances move from an area of lower concentration to an area of higher concentration, which is contrary to the natural direction of diffusion. The energy needed for this process typically comes from ATP (adenosine triphosphate), a molecule that cells produce during metabolism.
For example, in the case of sodium-potassium pumps, which are vital for nerve impulse transmission, energy from ATP is used to transport sodium ions out of the cell and potassium ions into the cell, thereby establishing necessary concentration gradients for cell function.