5. Investigating Mitosis

Question 1

how to prepare and stain root tip in order to obseve stages of mitosis

Answer 1

1. cut 1cm from tip of growing root
2. prepare boiling tube containing 1 M HCl and put in water bath at 60 C
3. transfer root tip to boiling tube and incubate for mins
4. use pipette to rinse root tip well with cold water. leave root tip to dry on a paper towel
5. place on microscopic slide and cut 2 mm from verty tip, get rid of rest
6. use mounted needle to break tip open and spread cells out thinly
7. add few drops of stain
8. place cover slip over and push down firmly to squash tissue
9. look at through optical microscope

Question 2

why use stain

Answer 2

makes chromosomes easier to see under microscope

Question 3

stains you can use

Answer 3

toludine blue O,
ethano-orcein (this requires tips to be fixed in ethanoic acid),
feulgen stain (this requires extra rinse

Question 4

why push cover slip down firmly to squash tissue

Answer 4

makes tissue thinner and allow light to pass through

Question 5

why shouldn’t you smear cover slip sideways

Answer 5

damage chromosomes

Question 6

formula for calculating mitotic index

Answer 6

number of cells with visible chromosomes / total number of cells observed

Question 7

what does a high mitotic index mean

Answer 7

lots of growth or repair

Question 8

what can get in the way of observations

Answer 8

artefacts (things that aren’t part of specimen)

dust, air bubble, fingerprints. need to prepare specimen carefully to avoid this