Cell Structure and Division - Cell Division - Investigating Mitosis

Question 1

INVESTIGATING MITOSIS PRACTICAL

- Staining Root Tips

Answer 1

• Wear gloves (because of stain use)
• Cut 1cm from the tip from a growing shoot (e.g. of an onion)
  It needs to be the tip because that’s where growth occurs (so where mitosis takes place).
• Prepare a boiling tube containing 1 M hydrochloric acid and put it in a water bath at 60 degrees C.
• Transfer the root tip into the boiling tube and incubate for about 5 mins.
• Use pipette to rinse the root tip well with cold water.
  Leave the tip to dry on a paper towel.
• Place the root tip on a microscopic slide and cut 2mm from the very tip of it. Get rid of the rest.
• Use a mounted needle to break the tip open and spread the cells out thinly.
• Add a few drops of stain and leave for a few minutes.
  The stain will make the chromosomes easier to see under a microscope.
• Place a cover slip over the cells and push down firmly to squash the tissue. This will make the tissue thinner and allow light to pass through it. Don’t smear the cover slip sideways or the chromosomes will be damaged.
• Now you can look at all the stages of mitosis under an optical microscope.

Question 2

What is the formula for mitotic index?

Answer 2

mitotic index =

number of cells with visible chromosomes
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total number of cells observed