Active transport requires energy to move substances across a plasma membrane, often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.
The sodium-potassium pump is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell, both against a concentration gradient, in order to maintain the proper concentrations of ions both inside and outside the cell, and to thereby control membrane potential.
Vesicle transport is a type of active transport that uses vesicles to move large molecules into or out of cells.
