Diffusion happens around us every day. When someone lights a fire in your community and soon you smell the smoke or when someone who is wearing perfume passes you and you smell it it is because of diffusion.
Diffusion is the movement of energy or particles from an area of higher concentration to an area of lower concentration. Diffusion of particles takes place most rapidly in gases, slower in liquids, and slowest in solids. The spreading of a scent throughout a room is a common example of gaseous diffusion.
A solid may dissolve and diffuse through a liquid, such as when you put a lump of sugar in a cup of water. This process is slower than the diffusion of a gas.
Diffusion processes also occur in living organisms. Digestion, for example, is a process of chemically converting food so that it will be able to pass, by diffusion, through the intestinal wall, and into the bloodstream.