What are the functions of the smooth and rough e. r.s

The endomembrane system is a group of cell membranes and organelles that are mutually interconnected, either by being directly continuous with one another or by sending one another vesicles—little spheres of membrane then can bud off from one membrane and fuse with another. 

The rough endoplasmic reticulum (rough ER) gets its name from the bumpy ribosomes attached to its cytoplasmic surface. As the ribosomes attached to the rough ER make proteins, they feed the newly forming protein chains into the lumen.

The smooth endoplasmic reticulum (smooth ER) does not have ribosomes on its cytoplasmic face.The smooth ER has a variety of functions, and its exact role may vary between cell types.

One role of the smooth ER is to produce lipids, including phospholipids, cholesterol, and steroids.