Osmosis and Diffusion
Osmosis can occur when there is a partially permeable membrane, such as a cell membrane. When a cell is submerged in water, the water molecules pass through the cell membrane from an area of low solute concentration to high solute concentration (e.g. if the cell is submerged in saltwater, water molecules move out; if it is submerged in freshwater, however, water molecules move in); this is called osmosis. The cell membrane is selectively permeable, so only necessary materials are let into the cell and wastes are left out. The word 'osmosis' is particular to the diffusion of water molecules into the cell.
Diffusion is the movenment of molecules from an area of high concentration to one of low concentration, during diffusion molecules move from an area of high concentration to an area of low concentration gradient until they are evenly balanced.