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 lipopolysaccharides, a part of which is integrated into the membrane lipids.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for 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

Answer: (A)

• 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 G +ve, i.e.those which give (+)ve gram stain.Gram-negative ,i.e ,those which give (-ve)gram stain .
• The composition of the bacterial cell wall is the basis of gram staining technique. The cell wall of gram (-ve) bacteria contain alcohol soluble lipids called lipopolysaccharides while the cell wall of gram +ve bacteria lack these lipids. Thus, gram +ve bacteria retain color and Gram-ve bacteria do not.
• Hence Gram-negative bacteria do not retain the stain when washed with alcohol because the outer face of the outer membrane of Gram-negative bacteria contains lipopolysaccharides, a part of which is integrated into the membrane lipids.
• So, the correct answer is 'Both Assertion and Reason are correct and Reason is the correct explanation for Assertion'.