Required practical - the effect of osmosis on plant tissue
Investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue
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 either:
- Observe (with a light microscopeDevice that uses visible light and a series of lenses to produce an enlarged image of an object.),cellBasic unit of life. Unicellular organisms only have one cell. Multicellular organisms have many cells. or tissueA group of similar cells that carry out the same function, eg muscle tissue. placed in solutionMixture formed by a solute and a solvent. 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.
- 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 – sodium chloride 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. Concentration is measured in moles. A 1.0 mol dm-3 solution of a substance contains moleThe amount of substance that contains the same number of particles as there are atoms in 12 g of carbon-12 (contains the Avogadro's constant 6.0 ×10²³ number of particles). of the substance per dm-3 of a solution, or one mole per litre of solution.
- To determine the concentration of the cell sapThe liquid found in the vacuole of plant cells, consisting of water with dissolved sugars, salts and amino acids. of potato cells.
- Independent Variable: The concentration of the sucrose solutions, with a range of 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol/dm-3.
- 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 0.0 mol/dm-3 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 resultA result that is very different from the rest of the 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 – do not cut the potato cylinders towards your hand.
- Care must be taken when using the scalpel.
- Wear eye protection when using chemical solutions.
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.
The effects on plant tissues at a cellular level can be observed using a microscope. Another way of looking at osmosis in plant cells is to mount a piece of onion skin, or beetroot on microscope slides in drops of different concentrations of sugar or salt. Observe the cells for a few minutes. It is easy to see the process of plasmolysedDescription of a plant cell in which the vacuole has shrunk and the membrane has pulled away from the wall due to water loss by osmosis. in beetroot because the cell sap is red.