2.5 Required practical 2

Question 1

What is the reasoning behind the practical

Answer 1

• Plant cells undergo mitosis at shoot and root tips in areas called meristems.
• Cells in the meristems are totipotent and retain the ability to differentiate.
• You can calculate the mitotic index by taking a sample from the tip of a plant root and observing it under a microscope.

Question 2

What is mitotic index

Answer 2

The ratio of cells undergoing mitosis to the total number of cells in a sample.

Question 3

Describe the method of the practical

Answer 3

1. Heat 1moldm-3 of HCl at 60 degrees in a water bath.
   - Cut a small sample of the root tip using a scalpel.
2. Transfer the root tip to HCl and incubate for 5 minutes.
3. Remove the HCl and wash sample in cold distilled water and remove the very tip using a scalpel.
4. Place the tip on a microscope slide and add a few drops of a stain (e.g. toluidine blue O).
5. Lower the cover slip carefully, making sure there are no air bubbles and that the coverslip doesn’t slide sideways.
6. Place under a microscope and set the objective lens on the lowest magnification.
7. 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 (use a higher mag if needed).
9. Count the total number of cells and the cells undergoing mitosis.

Question 4

What is the formula for calculating mitotic index

Answer 4

Mitotic index = number of cells undergoing mitosis/ total number of cells in the sample.

Question 5

Why is HCl used

Answer 5

It helps break apart the tissue so the cells can be seen better.

Question 6

Why is a stain used

Answer 6

This makes the chromosomes visible, so it will be easier to see which cells are undergoing mitosis.

Question 7

Why shouldn’t you move the coverslip sideways

Answer 7

This could damage the chromosomes.

Question 8

What are 4 hazards in this experiment

Answer 8

1. Hydrochloric acid
2. Stain (e.g. toluidine blue O stain)
3. Scalpel
4. Broken glass

Question 9

What are risks and precautions for HCl

Answer 9

• May cause harm/ irritation to eyes or in cuts.
• Wear eye protection and goggles. Avoid contact with skin.

Question 10

What are risks and precautions for the stain

Answer 10

• May cause harm/ irritation to eyes or in cuts.
• Wear eye protection and goggles. Avoid contact with skin.

Question 11

What are risks and precautions for the scalpel

Answer 11

• Cuts from sharp object.
• Cut away from fingers. Use forceps to hold the sample while cutting. Keep away from the edge of the desk.

Question 12

What are risks and precautions for broken glass

Answer 12

• Cuts from sharp object.
• Take care when handling slides and coverslips.
• Keep glassware away from the edge of the desk