Diffusion and osmosis are both processes of particle movement, but they differ in what moves and the presence of a membrane. Diffusion is the general movement of particles from an area of high concentration to low concentration, while osmosis is the movement of a solvent (usually water) across a semi-permeable membrane from an area of high solvent concentration to low solvent concentration. Diffusion: Definition: The net movement of particles from a region of higher concentration to a region of