week 4: lab 11 (gram staining)...

Question 1

What are the general steps of the gram stain?

Answer 1

1) other steps (creating a smear)
2) heat fix the smear
3) add primary stain (crystal violet)
4) Rinsed with water
5) Cover with mordant (Gram’s iodine)
6) Decolorization ( acetone alcohol)
7) counter stain (safranin)

Question 2

Is crystal violet (primary stain) an acidic or basic stain?

Answer 2

It is a basic stain so it will stain the cells on the slide.

Question 3

Why is the Gram’s iodine (mordant) used?

Answer 3

Mordants fixes the color in the cell or intensifies it.

Question 4

Why is the Alcohol (decolorization) and the Safranin (counterstain) useful in Gram staining?

Answer 4

The alcohol removes dye from the peptidoglycan layer by dissolving lipids in the outer membrane. It helps differentiate the gram negative and positive cells, with the use of the counterstain. The counterstain stains the Gram negative cells that became transparent after the decolorization step. These cause the Gram negative to become pink and it allows the Gram positive to stay purple (from the primary stain)

Question 5

What are the result colors?

Answer 5

Gram negative: Pink
Gram positive: Purple

Question 6

What are the differences of the Gram positive and negative cells?

Answer 6

1) The Gram negative cell has an outer membrane and a thin layer of peptidoglycan. The Gram positive has a think layer of peptidoglycan and no outer membrane.