Explain the term active transport?

Active Transport :  At intervals, protein assemblies involved in selective, or active transport of materials are inserted into the cell membrane. These specialized proteins use chemical energy to alter their chemical structure to pump molecules of dissolved substances into or out of the cell, from an area of low concentration of solute to a higher concentration, opposing the action of diffusion.

The part of the molecule to which the transported substance attaches is called the binding site. An example of active transport is the sodium-potassium pump, which is responsible for carrying electrical impulses down nerve cells, through contracting muscles, and in other control processes in cells. This process will be described more fully later.