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.