Core practical - Investigating osmosis in potatoes
Scientists investigate the effects of osmosisThe movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration. on living cells.
- They observe, with a light microscopeDevice that uses visible light and a series of lenses to produce an enlarged image of an object., cells or tissueA group of similar cells that carry out the same function, eg muscle tissue. placed in solutions of different concentrationThe concentration of a solution tells us how much of a substance is dissolved in water. The higher the concentration, the more particles of the substance are present..
- They also measure changes in cylinders or discs of fresh potato or beetroot. Cylinders will have a larger mass than discs, so scientists will have larger measurements to work with.
The following experiment investigates the effect of different concentrations of sucroseA disaccharide made from glucose and fructose. It is used as table sugar. on potato tissue. It could also be carried out using salt solution instead of sucrose.
Aims of the experiment
- To investigate the effect of a range of sucroseA disaccharide made from glucose and fructose. It is used as table sugar. solutions, on the mass of potato cylinders.
- To determine the concentration of the cell sap of potato cells.
- Independent Variable: The concentration of the sucrose solutions, with a range of 0%, 20%, 30%, 40%, 60%, 80% and 100%.
- Dependent variable: The change in mass of the potato cylinders.
- Control variables: The time that each cylinder is left in the sucrose solution, the size of each cylinder.
Method
- Set up 6 boiling tubes, each containing the same volume of one of the sucrose solutions. The 0% sucrose solution is distilled water. Label the boiling tubes.
- Prepare 6 potato cylinders using a borer and cut the cylinders to the same length. Gently dry each potato cylinder using a paper towel to remove excess liquid and record its mass before placing it into one of the boiling tubes.
- Leave the potato cylinders in the boiling tubes for 40 minutes.
- Remove each potato cylinder from its boiling tube, gently remove excess liquid from the surface of the cylinder with a paper towel and record its mass.
- If possible, repeat the experiment to obtain multiple values of mass change for each solution. Making a series of repeat measurements will enable you to identify and ignore any anomalous results and to calculate a meanThe mean is calculated by adding all of the data and dividing by the number of items of data..
Risks
- Make sure that the potato is placed on a ceramic tile when using the cork borer 鈥 do not cut the potato cylinders.
- Care must be taken when using the scalpel.
- Wear eye protection when using chemical solutions.
Results
This experiment shows the effect of osmosis on plant tissue. The cylinders will decrease or increase in mass if they lose or gain water by osmosis.