Which of the following is NOT a function of the endoplasmic reticulum?

The endoplasmic reticulum (ER) has several important functions within the cell, but ribosome production is not one of them. The ER is primarily involved in the synthesis and processing of proteins and lipids. The rough ER is studded with ribosomes, which are the actual structures responsible for assembling amino acids into proteins, while the smooth ER is associated with lipid production and detoxifying certain chemicals.

Ribosomes themselves are produced in the nucleolus of the nucleus, not the endoplasmic reticulum. Therefore, while the presence of ribosomes on the rough ER allows for protein synthesis, the ER does not produce ribosomes; it serves as a site where the proteins synthesized by ribosomes can be processed. Understanding the distinct roles of these cellular structures highlights why ribosome production does not fall under the purview of the ER's functions.