The movement of molecules and ions from a region of higher concentration gradient to the region of lower concentration gradient of the molecules. Its direction of movements depends totally on the direction of the concentration gradients.
Fick's Law is the principal law that underscores diffusion. And it sates that the rate of diffusion is directly proportional to the concentration gradients or differences; the surface area available for the molecules to pass through ;<u> but inversely proportional to the thickness of the separating membrane (diffusion distance. </u>
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Thus the larger the surface area exposed the more molecules pass through into the membrane , the higher the concentration differences the greater the number of molecules willing to break free and escape; but the thicker the separating membranes, the slower the number of molecules getting chances to pass through and the lower the rate of diffusion.
