Investigate the Effect of Varying Solution Concentration on Osmosis in a Potato Chip
A definition of osmosis is: 'the movement of water molecules from an
area of high water concentration to a low water concentration across a
semi-permeable membrane' (Oxforddictionary 2000).
In a high concentration of water the amount of solute (e.g. sugar) is
low. These solutions are usually known as a dilute or weak solution.
But in a low concentration of water the amount of solute (e.g. sugar)
is high. These solutions are usually known as concentrated or strong
When a weak solution and a strong solution are separated by a
partially permeable membrane, the water will move from the area of
high concentration to the area of low until both sides are equal. This
is osmosis, and is shown in the diagram below.
Examples of osmosis can also be seen in living cells. Root hairs on
plants take in water from the soil via osmosis. Water continuously
moves along the cells of the root and up the xylem to the leaf. Water
is moving to areas of lower water concentration all the time. This is
shown in the diagram below.
Example of Osmosis in a Root Hair Cell
When a cell is placed in distilled water which is high water
concentration water will move across the semi- permeable membrane into
the cell which has lower water concentration by osmosis, making the
cell swell in size. The cell is now known as turgid. If a potato cell
was placed in the same circumstances the cells would increase in
length, volume and mass because of the osmotic effects. If the same
potato cells were placed in a solution with a low water concentration,
then the effects would be the opposite - water would move out of the
cell into the area of lower concentration, the water. Thus, the potato
chip will decrease in length, volume and mass. In more extreme cases,
the cell membrane would break away from the cell wall and the cell is
then known as plasmolysed.
The higher the concentration of water in the external solution, the
higher the amount of water that enters the cell by osmosis. The
smaller the concentration of water in the external solution, the
higher the amount of water that leaves the cell. However, there will
be a point where the concentrations of water inside and outside the
cells are equal. This is known as the isotonic point, and at this
point there will be no change in the length, volume or mass of the
potato, as the net movement of water will be zero and no osmosis will
Using this information, I have come to the prediction that with a high
concentration of sucrose in the water, the mass of the potato will
decrease and the cells will become plasmolysed. In a low concentration
of sucrose the cells will become turgid.
I have based my prediction on a prelimary experiment we did amongst
our class, this experiment involved us placing potato chips into
various concentrations of sucrose solution and observing the potato's
change in mass...