Endoplasmic Reticulum is a network of intracellular membranes that is continuous with the nuclear envelope. Which statement is true?

• A. It is a network of intracellular membranes continuous with the nuclear envelope
• B. It is a single membrane-bound sac not connected to the nucleus
• C. It stores genetic material
• D. It synthesizes mitochondria

Answer: (A)

Endoplasmic reticulum is a network of interconnected membranous tubules and sacs that spans the cytoplasm. A defining feature is that its outer membrane is continuous with the nuclear envelope, so the ER is part of the same membrane system that surrounds the nucleus. This continuity places the ER in close relationship with nuclear functions and allows the ER lumen to connect with the perinuclear space. Because of this network, the ER serves as a major site for synthesis and processing of proteins and lipids: rough ER with ribosomes synthesizes secretory and membrane proteins, while smooth ER handles lipid synthesis and calcium storage. It is not a single isolated sac, nor does it store genetic material—the nucleus (and mitochondria) houses genetic material. It also does not synthesize mitochondria; mitochondria are separate organelles, though cellular membranes and lipids from the ER contribute to their membranes.