Gram staining differentiates bacteria based on:

A Size only

B Cell wall structure — gram-positive bacteria retain crystal violet dye due to thick peptidoglycan layer

C Motility

D Spore formation

✓ Correct Answer: Option B

Gram stain: crystal violet + iodine → decolorize → safranin. Gram+: thick peptidoglycan retains crystal violet (purple). Gram-: thin peptidoglycan, outer membrane, loses crystal violet, takes safranin (pink).

💡 Why is B) the correct answer?

The correct answer to the question "Gram staining differentiates bacteria based on:" is Option B: Cell wall structure — gram-positive bacteria retain crystal violet dye due to thick peptidoglycan layer.

The other options — A) Size only, C) Motility, D) Spore formation — are incorrect for this USMLE Exam Prep question. As explained above: Gram stain: crystal violet + iodine → decolorize → safranin. Gram+: thick peptidoglycan retains crystal violet (purple). Gram-: thin peptidoglycan, outer membrane, loses crystal violet, takes safrani…

📚 About This USMLE Exam Prep Practice Question

This 1-level USMLE Exam Prep question from the Step 1 - Basic Sciences topic is part of BrainForge Quiz's free exam preparation library. Each question includes the correct answer and a detailed explanation to help you understand the underlying concept, not just memorize the answer.

How to use this page: Read the question above, consider all four options (A through D), then check the highlighted correct answer and explanation. For active timed practice, start a free USMLE Exam Prep practice test or use flashcards for spaced repetition review.

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Gram staining differentiates bacteria based on:

✓ Correct Answer: Option B

📚 About This USMLE Exam Prep Practice Question

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