Cell Structure and Division- Investigating Mitosis

Question 1

How do you observe mitosis in a root tip?

Answer 1

1. Cut 1cm from a growing root tip (this is where growth occurs)
2. Prepare boiling tube containing 1M hydrochloric acid and put in water bath at 60 degrees C
3. Transfer root tip into boiling tube and incubate for 5 minutes
4. Use pipette to rinse root tip with cold water and leave tip to dry on a paper towel
5. Place root tip on microscope slide and cut 2mm from very tip
6. Use mounted needle to break tip open and spread cells very thinly
7. Add few drops of stain and leave for few minutes
8. Place cover slip over cells and push down firmly- don’t smear cover slip sideways or will damage chromosomes
9. Look at cells under an optical microscope

Question 2

How do you use an optical microscope to observe cells?

Answer 2

1. Clip the prepared slide onto stage
2. Select lowest-powered objective lens
3. Use coarse adjustment knob to bring stage up to just below objective lens
4. Look down eyepiece and use coarse adjustment knob to move stage downwards until image is in focus
5. Adjust focus with fine adjustment knob until there is a clear image

Question 3

How do you calculate mitotic index?

Answer 3

Mitotic index= number of cells with visible chromosomes/total number of cells observed

Question 4

What is the eyepiece graticule?

Answer 4

Fitted onto the eyepiece, like a transparent ruler with numbers but no units

Question 5

What is the stage micrometer?

Answer 5

Placed on the stage, microscope slide with an accurate scale, used to work out the value of divisions on the eyepiece graticule at a particular magnification

Question 6

How can you calculate the actual size?

Answer 6

Actual size= image size/magnification

Question 7

What are artefacts?

Answer 7

Things you can see down the microscope that aren’t part of the cell or specimen

Question 8

What can artefacts be?

Answer 8

Bits of dust, air bubbles and fingerprints, or inaccuracies caused by squashing and staining sample

Question 9

What are artefacts caused by?

Answer 9

Made during preparation of slides and shouldn’t be there at all

Question 10

How can you avoid artefacts?

Answer 10

Preparing root tip cells carefully

Question 11

Where are artefacts more common?

Answer 11

In electron micrographs because specimens need a lot of preparation before viewing under an electron microscope