RP03 ‐ Osmosis

• What is the aim of the osmosis practical?

  To investigate how different concentrations of sugar or salt solution affect osmosis in plant tissue, by measuring changes in mass or length.
• What is the first step of the osmosis practical?

  Cutting 5 equal-sized potato cylinders using a cork borer, trimmed to 3 cm and with the skin removed for consistency.
• Why is it important to trim the potato cylinders to the same size?

  To make the experiment fair by keeping the surface area and volume consistent.
• What is the second step of the osmosis practical?

  Blotting each potato cylinder with paper towel and recording its initial mass and length using a balance and ruler.
• Why do we blot the potato cylinders before measuring?

  To remove surface water so only osmosis-related mass changes are recorded.
• What is the third step of the osmosis practical?

  Labelling 5 boiling tubes and filling them with 10 cm³ of different sugar solution concentrations (e.g. 0.0M–0.8M).
• What is the fourth step of the osmosis practical?

  Submerging one potato cylinder into each boiling tube, making sure they are fully covered by solution.
• What is the fifth step of the osmosis practical?

  Leaving the test tubes in a rack overnight (or for a set time) to allow osmosis to take place.
• What is the sixth step of the osmosis practical?

  Removing the cylinders, blotting them dry with paper towels, then re-measuring and recording their mass and length.
• What is the seventh step of the osmosis practical?

  Calculating the percentage change in mass or length using:

  Percentage change = ((Final − Initial) / Initial) × 100
• What is the eighth step of the osmosis practical?

  Plotting a graph of percentage change vs concentration; where the line crosses the x-axis shows the concentration of cell sap (no net osmosis).
• What is osmosis?

  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
• What does a negative percentage change in mass mean?

  Water has moved out of the potato cells by osmosis because the solution was more concentrated than the cell sap.
• What equipment is needed to prepare the potato samples?

  Potato, cork borer, ruler, sharp knife, white tile.
• What equipment is needed to set up the sugar/salt solutions?

  Measuring cylinder, sugar solutions, distilled water, boiling tubes, test tube rack, labels.
• What equipment is needed for measuring and drying the potato cylinders?

  Top-pan balance, ruler, paper towels