Food-coloring dispersed in water illustrating diffusion. Dissolved molecules and ions are in constant, or Brownian, random motion, causing collisions between molecules, leading to a net movement from areas of high concentration to areas of low concentration. Diffusion continues until the molecules are evenly dispersed. In this example, equilibrium is acheived when the food coloring is evenly dispersed throughout the water in the glass container. Diffusion determines the movement of many important molecules into, through, and out of living cells.