Compare cell wall structure between Gram-positive and Gram-negative bacteria.

• A. Gram-negative have an outer membrane and LPS; Gram-positive have no outer membrane.
• B. Gram-positive have an outer membrane with LPS; Gram-negative have thick peptidoglycan and no outer membrane.
• C. Gram-positive have thick peptidoglycan and no outer membrane; Gram-negative have thin peptidoglycan and an outer membrane with LPS.
• D. Gram-positive lack peptidoglycan; Gram-negative lack outer membrane.

Answer: (C)

Cell wall architecture distinguishes Gram-positive and Gram-negative bacteria by two main features: the thickness of the peptidoglycan layer and the presence or absence of an outer membrane with LPS. Gram-positive bacteria have a thick peptidoglycan layer and no outer membrane, which helps retain the crystal violet stain during Gram staining. Gram-negative bacteria, on the other hand, have a thinner peptidoglycan layer and an outer membrane that contains lipopolysaccharide (LPS), located outside a periplasmic space. This outer membrane is absent in Gram-positive cells and contributes to differences in permeability and immune interactions.

The correct description captures both aspects: thick peptidoglycan with no outer membrane in Gram-positive, and thin peptidoglycan with an outer membrane containing LPS in Gram-negative. Other options either misstate the presence of the outer membrane or the peptidoglycan content, which is why they’re not as accurate.