Osmosis and Diffusion Part 1

Essential science - diffusion and osmosis

Diffusion

This can be defined as the process whereby liquids or gases of different

concentrations mix up with each other, when they are brought into contact,

until their concentrations are equal throughout. For example, if you take a

glass of clear water and put in a drop of ink, at first you will have an inky

area while the rest of the water will still be clear. However, over time, even

if you do not stir it up, the whole glass will become inky as the ink molecules

mix up with the rest of the water molecules in the glass.

This happens because the water and ink possess some heat energy. In

a hot object the molecules are vibrating; in fact the hotter the substance

the more vigorously the molecules will be vibrating. This is the difference

between a hot and a cold substance. In the hot substance the molecules

are vibrating more energetically than in the cold. The result of this molecular

movement is that the ink and water molecules vibrate into each other and

end up mixing in together until their distribution is equal throughout the

particular medium. The hotter the water the more rapidly the process of

diffusion will take place. Because diffusion requires the molecules to be

able to move relative to each other the process can only take place in

fluids (gases and liquids are both defined as fluids). This principle of

molecular vibration and heat is referred to as kinetic theory. Kinetic means

to do with movement.

Diffusion is a physical process which is essential for numerous

physiological processes. For example, the concentration of oxygen in the

air sacs of the lungs is higher than in the blood which is pumped to the lungs. Diffusion occurs in an attempt to make the concentration of oxygen

equal in the air and in the blood. This results in the movement of oxygen

from air into the blood. If this process were to suddenly stop we would all

die within a few minutes.

The rate at which diffusion occurs depends on several factors including

temperature, size and concentration of the particular molecules, pressure

and the area over which diffusion is free to occur.