Topic 3: Mitosis root squash core practical

Question 1

Why use the root tips in the mitosis root squash practical?

1 point

Answer 1

1. The highest levels of mitosis occur here in the root tip meristem where cells are actively dividing to produce new cells for growth

Question 2

Mitosis root squash practical method

9 steps

Answer 2

1. Cut off 5mm of onion/garlic root tip
2. Place cut root tip in hydrochloric acid on a watch glass for 5 mins
3. Wash root tips in water on a different watch glass
4. Use forceps to place the root tip on a microscope slide and macerate (squash to break apart cells) with a mounted needle
5. Add Toluidine blue stain and gently heat to intensify stain - leave for 30s then remove excess stain with paper towel
6. Place coverslip on slide and gently squash cells to obtain a single layer of cells
7. Observe cells under a microscope
8. Calculate mitotic index, repeat to calculate a mean (if relevant)
9. (Safety): Cut away from yourself when cutting root tip - to prevent cuts
   to skin. Hold the slide with forceps to heat- to prevent burns to skin

Note: you can use this method to compare mitosis in animal tissues, but thin/one cell thick layers of tissue would be required and acid/ maceration is unlikely to be needed (but read question)

Question 3

(Mitosis root squash practical)

Why is 5mm of root tip cut off? (1 point)

Answer 3

1. It is the site of {cell division / mitosis / actively dividing cells / meristem}

Question 4

(Mitosis root squash practical)

Why is the root tip placed in acid? (1 point)

Answer 4

1. To {soften the material / break middle lamella}

Question 5

(Mitosis root squash practical)

Why is the root tip macerated? (1 point)

Answer 5

1. Breaks apart cells to help obtain a single layer of cells

Question 6

(Mitosis root squash practical)

Why is Toluidine blue added to the macerated root tip? (1 point)

Answer 6

1. Makes chromosomes more visible

Question 7

(Mitosis root squash practical)

Why is the slide, with Toluidine blue on the macerated root tip, gently heated? (1 point)

Answer 7

1. Intensifies Toluidine blue stain

Question 8

(Mitosis root squash practical)

Why is the macerated root tip squashed under the coverslip? (1 point)

Answer 8

1. To obtain a single layer of cells

Question 9

(Mitosis root squash practical)

What is the purpose of the microscope? (1 point)

Answer 9

1. To magnify cells to enable chromosomes to be seen

Question 10

Give the risks paired with precautions of the root squash practical
(4 risks)

Answer 10

1. Cuts to skin from scalpel - Take care with scalpel, cutting away from you when cutting root tip
2. Skin/eye damage from acid or stain - Wear safety glasses and gloves when handling acid and stain
3. Burns when heating slide in Bunsen burner flame - Take care with Bunsen burner, hold slide with forceps, use yellow flame when not heating
4. Cuts to skin from glass slide or coverslip - Take care not to break the slide or coverslip and if they do break then do not touch broken glass

Question 11

What should you see under the microscope in the root squash practical?
(3 points)

Answer 11

1. Most cells that you observe down the microscope will be in interphase (the part of the cell cycle when the cell is not dividing) and chromosomes will not be visible
2. This is because interphase is a longer phase (in time) than the division phase (mitosis + cytokinesis) which is much shorter
3. Chromosomes will be visible in mitosis, but not in cytokinesis (as the DNA has decondensed in telophase).

Question 12

What is (1 point) and how do you calculate the mitotic index?
(give the formula)

Answer 12

1. The mitotic index gives the amount of cell division taking place in a tissue, so that different tissues can be compared.

Mitotic Index = (number of cells with visible chromosomes) / (total number of cells in the field of view)

Number of cells in the field of view = total number of cells that you can see

Number of cells with visible chromosomes – if chromosomes are visible, the cell is in one of the 4 stages of mitosis (not interphase)

If chromosomes are not visible the cell is in interphase

Question 13

What should you do if you are asked to compare mitosis in 2 different plant tissues? (eg. root and stem)
(3 things)

Answer 13

1. use tissues from cloned plants which are same age/species etc.
2. grow plants in same temperature, light intensity
3. repeat 5 times for each plant tissue to identify anomalies, calculate mitotic index and calculate a mean

Question 14

What should you do if you are asked to compare mitosis in plants grown in different conditions (light intensities, mineral ion concentrations, different soil types, different temperatures)?
(3 things)

Answer 14

1. use cloned plants (grown for 14 days in each condition)
2. same other conditions controlled (from list above)
3. repeat 5 times for each temperature/light intensity etc to identify anomalies, calculate mitotic index and calculate a mean