Let's begin with passive diffusion. So once again, passive diffusion means the molecule is either nonpolar, as the case is with cholesterol, or it's very small and only slightly polar, as the case is with water. And these types of molecules can simply move directly through our phospholipid bilayer, as the case is with cholesterol and water, without the use of any type of protein, and down the electrochemical gradient. So we use no energy. Let's move on to facility diffusion. This is shown in diagram one.