How does the rough Endoplasmic Reticulum differ from the smooth ER in structure and function?

The two differ in their function, and one is smooth and the other is rough.

Explanation:

The smooth endoplasmic reticulum (SER) is smooth, and the rough endoplasmic reticulum (RER) is rough.

Both the SER and RER are large continuous sheets of membrane that fold back on themselves to form an enclosed space (lumen). Think of this as like a cloth bag that has had its opening stitched closed and then the bag screwed-up to make a small ball

When viewed under an electron microscope shown in the RER looks rough as the surface is coated with ribosomes. The black dots, the ribosomes, are in the cytoplasm of the cell.