Practical 2

Question 1

Why do you use the equipment?

Answer 1

Hydrochloric acid- softens and loosens root tissue
Stain- to turn the chromosomes a purple-red colour so they become visible under the microscope
Mounted needle- To lower the cover slip + prevent air bubbles under the cover slip that would affect the ability to view the slide
Root tip- The tip is the growing region, so cells in this part should be undergoing mitosis

Question 2

Procedure to prepare a root tip slide

Answer 2

• Using scalpel cut off the tip of the root 5mm from the end
• Place root tip in a test tube of HCl + then into a water bath at 60°C for 10 mins to soften cells
• Remove from HCl + rinse with distilled water, place root tip on microscope slide + use filter paper to soak up any excess water
• Add a few drops os stain to root tip + using mounted needle, lower on cover slip + leave for 10 mins ( gives time for chromosomes to be stained)
• Place filter paper on top of the slide + gently press down. This stage spreads out the cells to get a single layer so light can pass through when viewing through the microscope

Question 3

Hazards + precautions

Answer 3

Scalpel- may cut yourself, so cut on top of a white tile to prevent slipping + cut away from you when slicing
HCl/stain- Irritant (HCl may be corrosive), so wear goggles + wash hands if it spills on you

Question 4

Mitotic index formula

Answer 4

Mitotic index = (number of cells in mitosis/ total number of cells) X 100

Question 5

When counting the cells to calculate the mitotic index, what should you do to ensure your count is accurate?

Answer 5

• Examine a large number of fields of view/ many cells
• To ensure representative sample