Osmosis and Diffusion | Introduction
Introduction
Gas and liquid moleculesThe smallest particle of a substance that retains all the properties of the substance and is composed of one or more atoms. are always in motion. They move randomly in all directions and bounce around and into each other. As they move, molecules have a tendency to spread out, moving from areas with many molecules to areas with fewer molecules. This process of spreading out is called diffusionRandom movement of molecules that leads to a net movement of molecules from a region of high concentration to a region of low concentration..
You have probably noticed diffusion in your home. If you opened a bottle of vanilla in your kitchen, for example, you probably could soon smell the vanilla in all parts of the room. The vanilla spread through the air from an area of high concentrationThe amount of a substance present in a given volume, such as the number of molecules in a liter. of vanilla molecules to areas of less concentration. They diffused throughout the room—and perhaps throughout the house.
OsmosisThe movement of fluids and substances dissolved in liquids across a semi-permeable membrane from an area of its greater concentration to an area of its lesser concentration until all substances involved reach a balance. (pronounced oz-MO-sis) is a kind of diffusion. Osmosis occurs when a substance diffuses across a semipermeableA thin barrier between two solutions that permits only certain components of the solutions, usually the solvent, to pass through.
membrane from an area of high concentration to an area of low concentration. A semipermeable membrane lets some substances through but not others.