Diffusion is important in many life processes.
Because of the random nature of the motion of molecules, the rate of diffusion of molecules out of any region in a substance is proportional to the concentration of molecules in that region, and the rate of diffusion into the region is proportional to the concentration of molecules in the surrounding regions. Thus, while molecules continuously flow both into and out of all regions, the net flow is from regions of higher concentration to regions of lower concentration. Generally, the greater the difference in concentration, the faster the diffusion. Since an increase in temperature represents an increase in the average molecular speed, diffusion occurs faster at higher temperatures. Diffusion often masks gravitational effects.