One of the roles of a membrane is to is regulate what goes in and out of the cell. There are various types of membrane transporters depending on the substance that is being transported. Active transporters usually transport small molecules such as ions. These transporters are driven by ATP. It moves substances against the concentration gradient. In passive diffusion, particles from areas of high concentration moves to lower concentration and does not require energy. Facilitated diffusion is the movement of molecules across cell membrane through protein channels. Exocytosis and Endocytosis are both transporters that require energy. Endocytosis is taking a substance or particle outside of the cell by engulfing it with the membrane. A membrane