Active transport is a biological process that moves molecules across a cell membrane against their concentration gradient. This means that substances are transported from areas of lower concentration to areas of higher concentration, which requires energy. Cells use energy in the form of ATP (adenosine triphosphate) to facilitate this movement, ensuring that essential nutrients and ions are absorbed efficiently. One common example of active transport is the sodium-potassium pump, which helps maintain the balance of sodium and potassium ions inside and outside of cells. By actively pumping sodium out and potassium into the cell, this mechanism is crucial for various cellular functions, including maintaining cellular homeostasis and supporting nerve impulse transmission.