The document discusses facilitated diffusion, a process where large polar molecules and ions pass through protein channels in the cell membrane rather than diffusing directly through the phospholipid bilayer. It notes that facilitated diffusion, like ordinary diffusion, is a passive process where molecules move from high to low concentration through protein channels. It also describes the two major types of integral membrane proteins involved - carrier proteins that bind and release specific solutes, and ion channels that contain gates to control permeability and allow ion currents across the membrane without binding.