Functions does active transport perform in a cell

Active transport refers to the process in which the cell uses its energy to transport materials in and out of the cell. This process occurs across the cell membrane. Since the liquid inside and outside of the cell are composed of different substances, the cell has to work extra and use some of its energy to maintain a proper balance of ions and molecules. Proteins that are attached to the lipid bilayer are responsible for doing much of the work in the process of active transport. 

Ithink that its like 15 mph.