Question

ASSERTION : Gram-negative bacteria do not retain the strain, when washed with alcohol.
REASON : The outer face of the outer membrane of Gram- negative bacteria contains lipopolysaccharides, a part of which is integrated into the membrane lipids.
A) Both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C) Assertion is correct but Reason is incorrect.
D) Both Assertion and Reason are incorrect.

Answer 1

Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane whilst Gram negative bacteria have a thin peptidoglycan layer and have an outer lipid membrane. The lipopolysaccharide consists of lipid A and O polysaccharide.

Complete answer:
To answer this question, first, we need to know about gram staining. Gram staining technique was developed by Danish Hans Christian Gram in 1884. It is a very useful procedure and on the basis of it bacteria can be classified into gram positive, i.e. those which give positive gram stain. Gram-negative i.e. those which give negative gram stain.

Now, let us find the solution from the option.
The composition of the bacterial cell wall is the basis of gram staining technique. The cell wall of gram negative bacteria contains alcohol soluble lipids called lipopolysaccharides while the cell wall of gram positive bacteria lacks these lipids. Therefore we can say that gram positive bacteria retain color and Gram negative bacteria do not.

So, gram-negative bacteria do not keep the color when washed with alcohol due to the fact that the outer face of the exterior membrane of Gram-negative bacteria consists of lipopolysaccharides, a part of which is integrated into the membrane lipids. So, both the Assertion and Reason are correct for the gram- negative bacteria staining.

Thus, the correct option is A. i.e. Both Assertion and Reason are correct and Reason is the correct explanation of Assertion..

Note: The stages included in gram staining are summarized as: The composition of bacterial cell wall is the basis for gram staining technique. The gram negative bacteria’s cell wall contains alcohol soluble lipids (lipopolysaccharides) whilst the cell wall of gram positive bacteria lacks these lipids, therefore, keeps the crystal violet, Iodine component used.