Rough Endoplasmic Reticulum Functions

Steps:

• Identify membrane X as rough endoplasmic reticulum (RER) in a typical animal cell diagram, distinguished by attached ribosomes.
• Recall RER's role in protein synthesis using ribosomes and initial folding.
• Note RER's involvement in transporting synthesized proteins via vesicles to Golgi apparatus.
• Match combined functions to option B.

Why B is correct:

• Rough ER performs protein synthesis on ribosome surfaces and transports proteins through its membrane-bound lumen, per cell biology definitions of organelle roles.

Why the others are wrong:

• A: Lipid synthesis occurs in smooth ER, not rough ER.
• C: Rough ER also transports proteins, not limited to synthesis.
• D: Rough ER also synthesizes proteins, not limited to transport.

Final answer: B