This type uses chemical energy (ATP) directly to move a substance. A classic example is the . It pumps three sodium ions out of the cell. It brings two potassium ions into the cell.
The most critical function of active transport is to create and sustain concentration differences of ions (such as sodium, potassium, calcium, and hydrogen) across the plasma membrane. For example, the sodium-potassium pump (Na⁺/K⁺ ATPase) actively pumps three sodium ions out of the cell and two potassium ions into the cell. This generates: active transport function