The main difference between the Rough Endoplasmatic Reticulum (RER) and the Smooth Endoplasmatic Reticulum (SER) is that the RER has attached to its surface ribosomes. This changes its appearence.
The RER and SER also differ in their function. Whereas the SER is involved in the synthesis and storage of lipids that are used in the generation of the cell membrane (includes cholesterol and phospholipids), the RER participates in the synthesis of enzymes and proteins.
