Diffusion and facilitated diffusion are two examples of passive transport. Passive transport is transport through a cell membrane that does not require energy. In either diffusion or facilitated diffusion, particles move down a concentration gradient. In other words, the particles move from areas of higher concentration to areas of lower concentration. The difference between diffusion and facilitated diffusion is that particles travel directly through the cell membrane in diffusion, whereas particles undergoing facilitated diffusion require specific transmembrane integral proteins.
On the other hand, active transport does require energy in the form of adenosine triphosphate (ATP). Energy is required during active transport because particles are pushed against their concentration gradient. In other words, particles that under active transport move from areas of lower concentration to areas of higher concentration. As in facilitated diffusion, particles undergoing active transport also travel through a carrier protein.