Crystal violet targets bacterial peptidoglycan for purple staining

Steps:

• Crystal violet binds to peptidoglycan, a polymer unique to bacterial cell walls, causing purple staining.
• Identify options: only bacteria possess peptidoglycan; eukaryotes like plants, animals, and protozoa do not.
• Vibrio cholerae is a bacterium, so its cell wall contains peptidoglycan.
• Eliminate non-bacterial options lacking peptidoglycan.

Why B is correct:

• Vibrio cholerae is a Gram-negative bacterium with a thin peptidoglycan layer that retains crystal violet dye, staining purple per Gram staining principles.

Why the others are wrong:

• A: Palisade mesophyll cells are plant cells with cellulose walls, lacking peptidoglycan.
• C: Plasmodium falciparum is a protozoan parasite without peptidoglycan in its structure.
• D: Endothelial cells are eukaryotic animal cells with no peptidoglycan.

Final answer: B