RP 2- Calculating mitotic index Flashcards
What is the mitotic index?
The ratio of cells undergoing mitosis to the total number of cells in a sample.
Describe one method
-Stand beaker on bench mat- add 10 ml of hydrochloric acid.(5 mol dm–3). Put some
paper towel on the bench mat and label.
- Place about 2cm of root tip in the acid and leave for 15 minutes.
- Set up microscope while waiting.
- Rinse root tip in distilled water in the watch glass.
- Cut off root tip (1mm) and place on a microscope slide.
- Cover the section with toluidine blue stain and macerate with the mounted needle to separate the cells. Use piece of white paper to aid colouration of roots.
- Continue to macerate until the tissue is well broken and the cells are stained dark blue.
- Add cover slip and with gentle finger pressure ‘spread’ the material and blot at the same time by using a folded filter paper piece between finger and slide.
- Look for cells undergoing mitosis.
- Record your data in a suitable table.
- Calculate the mitotic index.
Name and describe 3 potential risks of this experiment?
HCl acid is corrosive: could irritate eyes or skin= handle it with caution, wear eye protection, wash off skin immediately,
Scalpel: could cut yourself= cut away from fingers, elevate cuts and apply pressure.
Broken glass: could cut yourself= take care when handling coverslips, keep glassware away from glass edge, do not remove glass from wound.
Why did we only use the root tip?
This is where the cells undergoing mitosis are.
Why do we cut the root tip immediately before placing it in the acid?
To stop any reactions from occurring and to see some cells which are dividing.
Describe 2 improvements you could make to this method.
Use a plant which is faster growing so more cells should be visible in mitosis.
Use an even thinner root tip to show more cells which are dividing.
Why do we us HCl or alcohol?
To stop chemical reactions from occurring.
HCl breaks the H bonds that join the bases holding the 2 strands of DNA together, softening the tissue so it can be squashed.
Why was the sample stained?
To stain the chromosomes so they are visible.
Why did you firmly squash the sample of cells by pushing down on the coverslip?
In order to obtain a thin sample of cells so light from the microscope can penetrate through easier.
Why should the coverslip have not been pushed sideways?
So the chromosomes are not broken open.
Why is the root tip rinsed in the distilled water?
In order to get rid of any excess acid or alcohol.
