Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion. It describes the spread of particles through random motion from regions of higher concentration to regions of lower concentration. In diffusion, particles are propelled by thermal energy.


There is a special type of diffusion called osmosis. If two solutions of different concentration are separated by a semi-permeable membrane which is permeable to to the smaller solvent molecules but not to the larger solute molecules, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution. This process is called osmosis. Osmosis is of great importance in biological processes where the solvent is water. The transport of water and other molecules across biologicalmembranes is essential to many processes in living organisms.