Both diffusion and osmosis are processes concerning the movement of molecules from an area of high concentration to an area of low concentration, along a concentration gradient. Any type of molecule can move by diffusion, however osmosis is specifically the movement of water molecules from a high concentration of water to a low concentration of water. This movement of water via osmosis takes place across a partially permeable membrane, however this is not required for diffusion. Both processes are passive and do not require energy to take place.