Analyze the structural differences between gram-positive and gram-negative bacteria based on peptidoglycan thickness.

• A. Gram-negative bacteria have a thick peptidoglycan layer and lack an outer membrane.
• B. Gram-positive bacteria have a thin peptidoglycan layer and an outer membrane.
• C. Both gram-positive and gram-negative bacteria have equally thick peptidoglycan layers.
• D. Gram-positive bacteria have a thick peptidoglycan layer, while gram-negative bacteria have a thin peptidoglycan layer and an outer membrane.

Answer: (D)