the process in which the molecules of a substance move from an area of higher concentration to an area of lower concentration. Doesn"t require cell energl, but is the driving force of the movement of many substances across the cell membrane.
1:there is a higher concentration of solute on one side of the membrane than on the other
2: diffusion causes a net movement of solute particles from the side of the membrane with the higher solute concentration to the side with the lower solute concentration.
3: Once the equillibrium is reached solute particles continue to diffuse across the membrane in both directions but at approximately equal rates, so that there is no net change in solute concentration