Question

Assertion : Gram-negative bacteria do not retain the stain when washed with alcohol. 

Reason: The outer face of the outer membrane of Gram-negative bacteria contains lipopoly-saccharides, a part of which is integrated into the membrane lipids.

(a) Both A and R are true and R is the correct explanation of A.

(b) Both A and R are true but R is not correct explanation of A

(c) A is true but R is false

(d) A and R are false

Answer 1

The correct option is: (b)

Explanation:

Bacteria which retain blue or purple colour are known as Gram (+) bacteria (e.g., Bacillus subtills). Bacteria which do not retain and stain and become colourless are termed as Gram (-) bacteria (e.g.. Escherichia coli). (Gram-ve bacteria are commonly stained with safranin). Washing of the stain in Gram-ve bacteria is due to high lipid content of cell wall which gets dissolved in organic solvents like actone.