RP3

• What is the purpose of calibration curves?

  They are used to determine the concentration of an unknown sample by comparing it to a set of standard values with known concentrations.
• How is a calibration curve used to find the concentration of plant tissue?

  Plot a calibration curve of percentage change in mass against concentration.

  Find the x-intercept where the plant tissue is isotonic to the sucrose solution.
• How is a calibration curve used to find the concentration of plant tissue?

  Plot a calibration curve of percentage change in mass against concentration.

  Find the x-intercept where the plant tissue is isotonic to the sucrose solution.
• What occurs when plant tissue is placed in a hypotonic solution?

  Water moves into the plant tissue by osmosis, plant tissue increases in mass.
• Why are the potato discs left in solution for 20 minutes?

  To allow time for osmosis until the plant tissue reaches equilibrium with its surrounding solution.
• What is water potential determined by?

  The concentration of solutes.

  The higher the solute concentration then the lower the water potential.
• Outline the procedure of investigating osmosis using potato tissue.

  1. Make a simple dilution of 1M sucrose to produce 5 concentrations. Add 5 cm° to 5 different test tubes.
  2. Cut a potato into equal sized chips and weigh.
  3. Place a chip in each test tube and leave for 20 minutes.
  4. Take out, dab the excess water and weigh them again.
  5. Calculate the percentage change in mass.
• Why is the percentage change used rather than the actual change in mass?

  Potato chips may not all have same starting mass.

  Percentage change allows comparison.
• What is indicated by the x-intercept of the calibration curve?

  The concentration that is isotonic to the solution tested.
• Explain the change in mass in the potato chips.

  The potato chips with concentration lower than the sucrose solution (higher water potential) lose mass as there is a net movement of water out of the cells.

  The potato chips with concentration higher than the sucrose solution (lower water potential) gain mass as there is a net movement of water into the cells.
• Why are the potato chips dabbed dry after removing from the sucrose solution?

  To remove any excess water clinging to its surface.
• What are the controlled variables of this practical?

  Volume of sucrose solution

  Size of potato chips

  Length of time left in solution

  Dab each potato disc with paper towels