# DBT JRF 2022 — Question 32

Exam: DBT JRF 2022 · Section: B · Topic: Microbiology › Bacterial Cell Wall & Gram Staining · Difficulty: Medium

## Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A: Mycoplasma is a bacteria without cell wall, and it stains negative in Gram staining. Reason R: Only bacteria that have a cell wall would stain positive in Gram staining. In the light of the above statements, choose the correct answer from the options given below:

## Options

- **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 the correct explanation of A
- **C.** A is true but R is false
- **D.** A is false but R is true

## Answer

Option C

## Explanation

Mycoplasma, Gram staining, and cell wall: Assertion A: 'Mycoplasma is a bacterium without a cell wall, and stains negative in Gram staining.' — TRUE • Mycoplasma spp. naturally lack a cell wall (no peptidoglycan). • Without a cell wall to retain the crystal violet-iodine complex, they appear Gram-negative. Reason R: 'Only bacteria that have a cell wall would stain positive in Gram staining.' — PARTIALLY TRUE but MISLEADING • This is not a complete or correct explanation. Gram-NEGATIVE bacteria HAVE cell walls (with thin peptidoglycan and an outer membrane) but still stain Gram-NEGATIVE (because the outer membrane prevents retention of crystal violet). • So the mere presence of a cell wall does not guarantee Gram-positive staining. • R is not the correct explanation for A because Gram-negative wall bacteria also have cell walls. Answer: A is true but R is not the correct explanation of A (Option 2).

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