In a solution, particles move constantly. They collide with one another and tend to spread out randomly. As a result, the particles tend to move from an area where they are more concentrated to an area where they are less concentrated during a process known as diffusion. When the concentration of the solute is the same throughout the system, the system has reached equilibrium. Osmosis is the diffusion of water through a selectively permeable membrane. In this activity, students will observe how osmosis affects a plant cell.