RP 2- mitosis

Question 1

what is the mitotic index?

Answer 1

number of cells in mitosis/ total no of cells

Question 2

what are the steps of the root tip squash practical?

Answer 2

1) stand watch glass on bench mat and add approx. 1ml of HCl (5 mol dm-3) and do this in a fume cupboard
2) place 2cm of root tip in the acid and leave for 15 minutes
3) set up microscope while waiting
4) rinse root tip in distilled water in the watch glass, hold with forceps to keep in place.
5) cut 1mm off the root tip and place on slide
6) add a drop of Toluidine blue stain and macerate with mounted needle to separate the cells
7) continue to macerate until tissue is well broken and cells are stained dark blue
8) place cover slip on top and gently spread the material and blot at the same time by using folded piece of paper between finger and slide
9) look carefully for cells undergoing mitosis, chromosomes should stain dark blue. count no. of cells in mitosis. repeat for several fields of view
10) record results in a table and use table to calculate mitotic index

Question 3

why was it necessary to use acid?

Answer 3

1) the acid breaks down pectins which hold the cell walls together
2) allows full maceration of the sample
3) denatures spindle fibres to stop mitosis

Question 4

Why do you need to squash the onion root tip?

Answer 4

so that chromosomes of individual cells can be observed.

Question 5

why use root tips in mitosis experiments?

Answer 5

They are sites of rapid growth, so the cells are dividing rapidly in areas called meristems