What is the major function of the endoplasmic reticulum?

• A. Synthesize lipids.
• B. Dissolve waste products.
• C. Generate energy as ATP.
• D. Transport synthesized proteins to the Golgi apparatus.

Answer: (D)

Proteins destined for secretion or membranes begin on ribosomes attached to the rough endoplasmic reticulum, where they are synthesized and properly folded. These newly made proteins are then packaged into transport vesicles that bud from the ER and move to the Golgi apparatus, where they’re modified, sorted, and directed to their final cellular destinations. This movement of synthesized proteins from the ER to the Golgi is a defining step in how cells process and ship proteins, making it the best answer. The other options align with functions of other organelles or specific ER regions—lipid synthesis occurs mainly in the smooth ER, waste dissolution is a lysosomal function, and ATP generation happens in mitochondria.