What is synthesized by the smooth endoplasmic reticulum?

The smooth endoplasmic reticulum (SER) is primarily involved in the synthesis of lipids and carbohydrates. Unlike the rough endoplasmic reticulum, which is studded with ribosomes and primarily synthesizes proteins, the smooth ER lacks these ribosomes and instead focuses on lipid metabolism. It plays a crucial role in the synthesis of phospholipids, which are essential for creating cellular membranes, as well as steroid hormones.

Additionally, the smooth ER is involved in the detoxification of chemicals and the storage of calcium ions. The presence of enzymes in its membrane—responsible for lipid and carbohydrate metabolism—further emphasizes its role in synthesizing these important biomolecules. Thus, the correct answer highlights the smooth endoplasmic reticulum's critical function in producing lipids and carbohydrates, which are key components of cell structure and energy storage.