Required Practical 2 - Preparation of Stained Root Tip Squash

Question 1

Suggest why an optical microscope is used

Answer 1

Has a high enough magnification to view chromosomes

Question 2

Suggest why root tip is gently squashed onto microscope slide

Answer 2

• gently to avoid damage to cells

- thin layer of cells to take up better stain and for light to penetrate easily to clear observation

Question 3

Suggest why root tip is soaked in hydrochloric acid

Answer 3

• necessary to dissolve middle lamella

- cells spread easily for clear observations

Question 4

Suggest why root tip is heat treated

Answer 4

Allows chromosomes to take a deeper stain

Question 5

Suggest the purpose of a stain and give an example

Answer 5

• Toluidene/Orcein

- easily identify chromosomes with DNA due to contrast

Question 6

Suggest why a root tip is used to observe mitosis

Answer 6

• contain meristem tissue

- cells undergo regular mitosis

Question 7

Suggest why the root tip of onion, garlic or shallot is usually used

Answer 7

• easy to grow in large numbers

- can take up stain and be flattened onto slide

Question 8

Suggest why it is important the coverslip is not moved side to side

Answer 8

• avoid breaking chromosomes

- avoid overlapping/rolling cells

Question 9

Suggest why it is sensible to mount both sides of root tip

Answer 9

• easy to confuse ends

- cells behind the meristem elongate and are easier to differentiate under the microscope

Question 10

Describe how you could make a temporary mount of a piece of plant tissue to observe starch grains using an optical microscope

Answer 10

• cut a thin slice of plant tissue
• place on a glass side using forceps and add a drop of water
• add a few drops of iodine (or other appropriate stain)
• lower coverslip using a mounting needle