required practical 2

Question 1

what is practical 2

Answer 1

preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify the stages of mitosis in these stained squashed and calculation of a mitotic index

Question 2

aim - required practical 2

Answer 2

plant cells undergo mitosis at shoot and root tips in areas called meristems

cells in the meristem are totipotent and retain the ability to differentiate

the mitotic index of a sample is the ratio of cells undergoing mitosis to the total number of cells in a sample

to find the mitotic index, cells from the meristem must be viewed under an optical microscope

Question 3

practical 2 equipment list

Answer 3

optical microscope

microscope slides and cover slips

water bath

hydrochloric acid

Toluidine blue O stain

distilled water

scalpel

forceps

100ml beaker

root tip

Question 4

practical 2 - method

Answer 4

1. Heat 1 mol dm​-3 H​ Cl at ​60​​°C​​ in a water bath.
2. C​ut a small sample of the ​root tip​​ using a ​scalpel​​.
3. Transfer root tip to ​HCl​​ and ​incubate​​ for 5 minutes.
4. Remove from HCl and wash sample in cold distilled water and ​remove the very
   tip ​​using a scalpel.
5. Place tip on a microscope slide and add a few drops of ​stain​​ (e.g. ​toluidine blue
   O​​). This makes the ​chromosomes visible​​ and will therefore show which cells are undergoing mitosis.
6. Lower the cover slip down carefully onto the slide. Make sure there are ​no air
   bubbles ​​in the slide which may distort the image, and that the​ coverslip doesn’t
   slide sideways which could damage the chromosomes.
7. Place under a microscope and set the ​objective lens​​ ​​on the lowest
   magnification.
8. Use the ​coarse adjustment knob​​ ​​to move the lens down to just above the slide.
9. Use the ​fine adjustment knob​​ ​​to carefully re-adjust the focus until the image is clear​​ (you can use a higher magnification if needed).
10. To calculate ​mitotic index​​, ​​cells ​undergoing mitosis​​ must be counted (cells with ​chromosomes visible​​), as well as the​ total number of cells

Question 5

2 - mitotic index

Answer 5

number of cells with visible chromosomes / total number of cells in sample

Question 6

2 - risk assessment

Answer 6

hydrochloric acid

Toluidine blue O stain

Scalpel

Broken glass