cpac 3

• Meristem


  Areas in shoot and root tips where plant cells undergo mitosis
• Totipotent


  Cells in the meristems retain the ability to differentiate
• Mitotic index


  Ratio of cells undergoing mitosis to the total number of cells in a sample
• Finding the mitotic index

  1. View cells from the meristem under an optical microscope

  2. Observe the number of cells undergoing the various stages of the cell cycle

  3. Calculate the relative length of these different phases
• Equipment


  • Optical microscope
  • Microscope slides and cover slips
  • Water bath (55 °C)
  • White tile
  • Paper towels
  • Stop clock
  • Hydrochloric acid (1 mol dm^-3 HCl)
  • Acetic orcein stain
  • Distilled water
  • Scalpel
  • Dissecting needles
  • Scissors
  • Root tip (garlic)
  • Small bottle
• Method


  1. Heat 1 mol dm^-3 HCl at 55°C in a water bath for 15 minutes

  2. Place the garlic clove in the bottle of HCl and leave it for 5 minutes

  3. Cut a small sample of the root tip, 5-10mm in length, using a scalpel

  4. Transfer root tip to acetic orcein stain and heat in the water bath for 5 minutes

  5. Place tip on a microscope slide. Macerate with a needle to spread the cells out

  6. Lower the cover slip down carefully onto the slide

  7. Place under a microscope and set the objective lens on the lowest magnification, then use the coarse adjustment knob to move the lens down to just above the slide

  8. Use the fine adjustment knob to carefully re-adjust the focus until the image is clear

  9. Count the cells in the various stages of mitosis and divide this by the total number of cells to calculate the percentage of the total cell cycle that stage represents

  10. To calculate mitotic index, cells undergoing mitosis must be counted (cells with chromosomes visible), as well as the total number of cells
• Hazards


  • Hydrochloric acid
  • Acetic orcein
  • Scalpel
  • Broken glass
• Hydrochloric acid


  May cause harm/irritation to eyes or in cuts
• Acetic orcein


  May cause harm/irritation to eyes or in cuts
• Scalpel


  Cuts from sharp object
• Broken glass


  Cuts from sharp object
• Safety Precautions


  • Wear eye protection; avoid contact with skin
  • Cut away from fingers; use forceps to hold sample whilst cutting
  • Take care when handling slides and coverslips; keep glassware away from edge of desk
• Emergency Procedures


  • Wash off skin immediately; flood eye/cuts with cold water
  • Elevate cuts; apply pressure; seek medical assistance
  • Elevate cuts; apply pressure; do not remove glass from wound; seek medical assistance
• Risk level for all hazards is low