Which statement about endoplasmic reticulum is true?

• A. Rough ER has ribosomes; Smooth ER has none.
• B. Rough ER lacks ribosomes; Smooth ER has many.
• C. The ER is the site of DNA storage.
• D. The ER functions primarily in energy production.

Answer: (A)

The main idea here is distinguishing the two forms of the endoplasmic reticulum. The rough endoplasmic reticulum has ribosomes on its surface, which is why it appears “rough” and is a major site for synthesizing proteins destined for secretion or for membranes. The smooth endoplasmic reticulum lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage in some cells. The other statements are incorrect because DNA is stored in the nucleus, not the ER, and energy production mainly occurs in mitochondria, not the ER. So the statement that the rough ER has ribosomes and the smooth ER has none accurately reflects their distinct roles.