SER (Smooth endoplasmic reticulum):
(1)Smooth endoplasmic reticulum does not have ribosomes and is composed of vesicles and tubules.
(2)It synthesises steroids and lipids e.g., fat cells, lipid secretory cells of liver. It is related to secretion.
RER (Rough endoplasmic reticulum):
(1)Rough endoplasmic reticulum have ribosomes on its outer surface and is composed of cisternae.
(2)Its main function is protein synthesis due to the presence of ribosomes on it, i.e., liver, pancreas cells.