The ability of Prokaryotic microorganisms to move compounds into the cell, and to remove waste products of metabolism out of the cell, is crucial for the survival of the cell. Some of these functions are achieved by the presence of water-filled channels, particularly in the outer membrane of Gram-negative bacteria, which allow the diffusion of molecules through the channel. But this is a passive mechanism and does not involve the input of energy by the bacterium to accomplish the movement of the molecules across the membrane. Mechanisms that depend on the input of energy from the microorganism are active membrane transport mechanisms.

Prokaryotic membrane transport depends on the presence of specific proteins. These proteins are located within a membrane that surrounds the cell. Gram-positive bacteria have only a single membrane surrounding the contents of the bacterium. So, it is within this membrane that the...