What cellular structure would be enlarged in cells that produce a lot of lipids for membranes?

The smooth endoplasmic reticulum (smooth ER) is the correct answer because its primary function is to synthesize lipids, including phospholipids and cholesterol, which are essential components of cellular membranes. Cells that are heavily involved in lipid production, such as those in the adrenal glands, liver, and certain types of glandular tissue, have a well-developed smooth ER that is enlarged to accommodate heightened lipid synthesis and processing.

In contrast, the rough endoplasmic reticulum is primarily involved in the synthesis of proteins, as it is studded with ribosomes that translate mRNA into polypeptide chains. The Golgi apparatus functions in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles, but it does not synthesize lipids directly. Lysosomes contain enzymes that break down waste materials and cellular debris; they do not play a role in lipid synthesis. Therefore, the enlarged smooth ER in cells that produce a lot of lipids reflects their specialized functions in membrane formation and lipid metabolism.