Active transport:

Active Transport is the movement of molecules from an area of lower concentration to an area of higher concentration. This movement against the concentration gradient requires energy in the form of ATP.

Functions of Active Transport:

In this process carrier proteins in the cell membrane use energy to move the molecules against the concentration gradient. For example, the membranes of nerve cells have carrier proteins in the form of a “Sodium-potassium pump”. In resting (not conducting nerve impulse) nerve cells, this pump spends energy (ATP) to maintain higher concentrations of K+ and lower concentrations of Na+ inside the cell. For this purpose, the pump actively moves Na+ to the outside of the cell where they are already in higher concentration. Similarly, this pump moves K+ from the outside to the inside of the cell where they are in higher concentration.