RP2

• Describe how to prepare squashes of cells from plant root tips?

  1. Cut a thin slice of root tip using a scalpel and mount onto a slide
  2. soak root tip in HYDROCHLORIC ACID then rinse
  3. Stain for DNA e.g with toluidine blue
  4. Lower coverslip using a mounted needle at 45 degree without trapping air bubbles
  5. Squash by firmly pressing down on glass slip but do not push sideways
• Why are root tips used?

  Where dividing cells are found/ mitosis occurs
• Why is a stain used?

  To distinguish chromosome

  • not Visible without a stain
• Why squash / press down on cover slip?

  • spread outs the cell to create a single layer of cells
  • so light passes through to make chromosomes visible
• Why not push cover slip sideways ?

  Avoid rolling cells together/ breaking chromosomes
• Why soak roots in acid?

  • seperate cells/ cell walls
  • to allow stain to diffuse into cells
  • to allow cells to be more easily squashed
  • to stop mitosis
• How to set up and use an optical microscope

  1. Clip slide onto stage and turn on light
  2. select lowest power objective lens (usually x4)
  3. use coarse focusing dial to move stage close to lens or away until image comes into focus
  4. adjust fine focusing dial to get clear image
  5. swap to higher power objective lens, then refocus
• Suggest how to calculate the time cells are in a certain phase of mitosis?

  1. Identify proportion of cells in named phase at any one time
  2. (NUMBER OF CELLS IN THAT PHASE / TOTAL NUMBER OF CELLS OBSERVED) X LEGNTH OF CELL CYCLE