Which statement correctly describes rough endoplasmic reticulum structure?

• A. It is a network of tubules and sacs with ribosomes on the surface.
• B. It contains no ribosomes and is smooth.
• C. It is not connected to the nuclear envelope.
• D. It functions primarily in energy production.

Answer: (A)

Rough endoplasmic reticulum is a network of flattened sacs and tubules studded with ribosomes on its cytosolic surface. That ribosome coverage gives it a “rough” appearance and underpins its role in synthesizing proteins destined for secretion, membranes, or lysosomes. The rough ER is also physically continuous with the outer membrane of the nuclear envelope, forming a continuous membrane system between the nucleus and cytoplasm. This combination of ribosome-coated surface and continuity with the nuclear envelope is what defines its structure. It’s not involved primarily in energy production—that role belongs to mitochondria—and the smooth endoplasmic reticulum, which lacks ribosomes, handles lipid synthesis and detoxification.