In eukaryotic cells, what is the key structural and functional difference between rough endoplasmic reticulum (rough ER) and smooth endoplasmic reticulum (smooth ER)?

• A. Rough ER is surrounded by a double membrane and contains DNA, whereas smooth ER is a single-membrane organelle that packages proteins for secretion.
• B. Rough ER is the primary site of ATP production, whereas smooth ER contains the enzymes for glycolysis.
• C. Rough ER lacks ribosomes and primarily carries out lipid synthesis, whereas smooth ER is covered with ribosomes and synthesizes secreted proteins.
• D. Rough ER is studded with ribosomes and is a major site of synthesis/processing for secreted and membrane proteins, whereas smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification.

Answer: (D)