Required practical 2 - mitotic index from stained root tip

Question 1

Describe how to prepare squashes of cells from plant root tips

Answer 1

1.Cut a thin slice of root tip (5mm from end) using scalpel and mount on to a slide

2. Soak root tip in hydrochloric acid then rinse
3. Stain for DNA (eg. with toluidine blue)

4.Lower cover slip using a mounted needle at 45 degree angle without trapping air bubbles

5. Squash by firmly pressing down on glass slip but do not push sideways

Question 2

Explain why root tips are used

Answer 2

● Where dividing cells are found/mitosis occurs

Question 3

Explain why a stain is used

Answer 3

● To distinguish chromosomes

● Chromosomes not visible without stain

Question 4

Explain why the cover slip needs to be
squashed /pressed down

Answer 4

● (Spreads out cells) to create a single layer of cells

● So light passes through to make chromosomes visible

Question 5

Explain why the coverslip should not be
pushed sideways

Answer 5

● Avoid rolling cells together/ breaking chromosomes

Question 6

Give two reasons why the roots should
be soaked in acid

Answer 6

● Separate cells /cell walls

● To allow stain to diffuse into cells

● To allow cells to be more easily squashed

● To stop mitosis

Question 7

Describe how to set-up and use an optical microscope

Answer 7

1. Clip slide onto stage and turn on light
2. Select lowest power objective lens (usuallyx4)

3 a. Use coarse focusing dial to move stage close to lens
b. Turn coarse focusing dial to move stage away from
lens until image comes into focus

4. Adjust fine focusing dial to get clear image
5. Swap to higher power objective lens ,then refocus

Question 8

What are the rules of scientific drawing?

Answer 8

Look similar to specimen/image-draw parts
to the same scale/ relative size

No sketching- only clear, continuous lines

No shading/hatching

Include a magnification scale (eg.x400)

Label with straight, uncrossed lines