In facilitated diffusion, molecules diffuse across the plasma membrane through using membrane proteins such as channel and carrier proteins. The ion or molecules bind to the active site of carrier proteins. The carrier protein then changes shape and releases the molecule on the other side of the membrane. Facilitated diffusion specifically transports large and polar molecules such as glucose, which on their own cannot pass through the membrane. Thus, use carrier and channel proteins. Molecules move down their concentration gradient from a region of higher concentration to a lower concentration. Since molecules move along their concentration gradient, no direct energy source is required for this type of diffusion. Examples of facilitated diffusion include ion transport, glucose and amino acid transport, and gas transport.