require practicals

• • Peel a one-cell layer of skin from an onion using a scalpel and tweezers.
  • Place this on a microscope slide, add a drop of iodine to stain the cells, place a cover slip on top, and place on the microscope stage.
  • Turn on the light or position mirror so light reflects through the condenser to the slide.
  • Use the lowest magnification objective lens.Use the coarse and fine focus knobs to focus.Increase magnification and refocus if needed.
  • A graticule on the slide can allow you to measure the length of cells in micrometers (um)e.g. a length of 2.5 um = 2.5x10 m
• Experiment procedure

  1. Cut equal size cylinders from potato and remove any skin (non-permeable)

  2. Remove excess water from surface and weigh using top-pan balance

  3. Place each in a test tube with different concentrations of sugar solution, and leave for a set time (e.g. 1 day)

  4. Water will move in or out of the cells due to osmosis

  5. Remove cylinders, dab off excess water, reweigh and calculate
• Where the line of best fit meets the x-axis is the concentration in the potato, as there would be no (net) movement of water in/out
• Controls

  • Size/shape of cylinders
  • Same vegetable
  • Volume of solution
  • Time