Which organelle is primarily involved in the synthesis of lipids?

The smooth endoplasmic reticulum (SER) is primarily involved in the synthesis of lipids. This organelle plays a crucial role in lipid metabolism, including the production of phospholipids and cholesterol, which are essential components of cell membranes. Additionally, the smooth endoplasmic reticulum is involved in the detoxification of drugs and poisons and the storage of calcium ions, further demonstrating its diverse functions within the cell.

In contrast, while the Golgi apparatus plays a significant role in modifying, sorting, and packaging proteins and lipids produced in the endoplasmic reticulum, it is not directly involved in their synthesis. Ribosomes, on the other hand, are the sites of protein synthesis, and the rough endoplasmic reticulum primarily specializes in producing proteins that are either secreted from the cell or incorporated into membranes, not lipids. Therefore, the smooth endoplasmic reticulum stands out as the critical organelle for lipid synthesis within the cell.