The correct answer is: smooth endoplasmic reticulum (smooth ER).
Smooth endoplasmic reticulum is a membrane organelle of the eukaryotic
cells which consists of tubular membrane vesicles. One of its main function is the synthesis of lipids and their storage. For example, cholesterol and phospholipids are stored in the smooth ER and then used for the synthesis of plasma membrane.
There is another type of ER- rough ER. The difference between these two ER on its outer surface have attached ribosomes- protein-synthesizing particles .
