RP2- Microscopy

Question 1

A student prepared a stained squash of cells from the root tips of garlic to calculate a mitotic index. He:
1. cut the end 5 mm from 10 garlic roots
2. placed the root tips into a Petri dish containing 5 cm3 of hydrochloric acid for 12 minutes
3. rinsed the root tips in distilled water
4. placed one of the root tips on a microscope slide and added toluidine blue stain
5. placed a coverslip onto the microscope slide, and gently pressed the coverslip downwards on the root tip
6. observed the root tip using an optical microscope.
Suggest why the student soaked the root tips in hydrochloric acid in step 2. (2)

Answer 1

• break down/ hydrolyse cell wall
• stain ✔ pass into cells
• stop mitosis

Question 2

A student prepared a stained squash of cells from the root tips of garlic to calculate a mitotic index. He:
1. cut the end 5 mm from 10 garlic roots
2. placed the root tips into a Petri dish containing 5 cm3 of hydrochloric acid for 12 minutes
3. rinsed the root tips in distilled water
4. placed one of the root tips on a microscope slide and added toluidine blue stain
5. placed a coverslip onto the microscope slide, and gently pressed the coverslip downwards on the root tip
6. observed the root tip using an optical microscope.
Other students in the class followed the same method, but calculated different mitotic indices.
Apart from student errors, suggest two explanations why. (2)

Answer 2

• tips from diff plants
• single field of view x representative of a root tip
• roots - diff age
• diff fields of view from diff parts of root tip
• cells undergo mitosis at diff rates