Download Diffusion, Osmosis and Turgor Pressure

Diffusion, Osmosis and Turgor Pressure
Diffusion is the movement of particles from an area of high concentration to an
area of low concentration or down the concentration gradient. We saw this happen in
class when the drop of red food colouring, put into a beaker of water, diffused
throughout the water. Other examples of this would be the how the smell of burnt
toast or Axe spreads throughout a house or the way a sugar cube dissolves in water.
Diffusion occurs in a fluid system because the particles in a solution are always moving.
A substance always moves from an area of high concentration to an area of low
concentration until the substance is equally distributed in the solution; equilibrium.
When the solution has an equal concentration throughout, it is said to be completely
diffused and at equilibrium.
Osmosis is a special case of diffusion. It is that the movement of water
molecules, from an area of high concentration to an area of low concentration (or
down the concentration gradient), through a selectively permeable membrane. The
movement of water into and out of cells is vital to living things, and is driven by
imbalances in concentrations. In a grocery store, the vegetables are sprayed with water
because the air surrounding the vegetables has a low concentration of water. To reach
a state of equilibrium, the water in the vegetables moves out of the cells making them
limp. Spraying the vegetables keeps the concentration of water surrounding the
vegetables high and prevents the loss of water, across the cell membrane, out of the
plant by the process of osmosis.
Turgor pressure is the pressure exerted by the contents of the cell against the
cell wall. When a plant cell has a large amount of water in the cell, the turgor pressure
is high. Plants like celery or lettuce are crisp when turgor pressure is high. When turgor
pressure is low, cells have lost the water that made the contents of the cell push
against the cell wall. This lack of pressure causes the tissues to become limp and the
plant appears wilted. Below are diagrams of a plant cell with high turgor pressure and
one with low turgor pressure.
high turgor pressure
low turgor pressure