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.

Hard

Solution

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Correct option is
A

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

  • 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'.

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