Practicals

Question 1

Describe method for practical observing stages of mitosis

Answer 1

1. Cut a 5mm sample of the root tip using a scalpel.
2. Transfer root tip to sample tubes containing HCl and leave for 5 minutes.
3. Transfer to watch glass containing cold distilled water. Leave for 5 minutes.
4. Dry root tips on filter paper.
5. Place tip on a microscope slide. Macerate with a needle to spread the cells out.
This makes the chromosomes visible and will therefore show which cells are undergoing mitosis.
6. Add a drop of toluidine blue to the slide and leave to stain for 2 minutes.
7. Lower the cover slip down carefully onto the slide. Make sure there are no air bubbles in the slide which may distort the image, and that the coverslip doesn’t slide sideways which could damage the chromosomes.
8. Wrap in a paper towel and gently ‘squash’ the slide.
9. 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.
10. Use the fine adjustment knob to carefully re-adjust the focus until the image is clear (can use a higher magnification if needed).
11. To calculate mitotic index, cells undergoing mitosis must be counted (cells with chromosomes visible), as well as the total number of cells.

Question 2

How is mitotic index calculated?

Answer 2

Number of cells with visible chromosomes / total number of cells in sample

Question 3

Where does mitosis take place in plants?

Answer 3

Meristems, totipotent cells