Prokaryotes do not have well-developed cell organelles, they have primitive bodies that govern the cellular functions of prokaryotic organisms.
The endoplasmic reticulum is a single membrane-bound cell organelle that aids in protein synthesis (RER) and lipid synthesis (SER).
The ER that is closely associated with the nucleus has got ribosomes on it and such type of ER is called Rough Endoplasmic Reticulum (RER). Such ER synthesizes protein.
The type of ER that is smooth in appearance and has got no ribosomes on it and such type of ER is called Smooth Endoplasmic Reticulum (SER). Such ER synthesizes lipid.
It is only present in a eukaryotic cell, therefore it is absent in prokaryotic cells such as bacteria.