The endoplasmic reticulum is the network or of tiny tubular structures scattered in the cytoplasm. The endoplasmic reticulum is generally of two types smooth and rough endoplasmic reticulum. The rough endoplasmic reticulum has  ribosomes attached to it whereas the smooth endoplasmic reticulum does not have ribosomes. The rough ER is generally found in cells actively involved in protein synthesis. Lipid synthesis is associated with the smooth endoplasmic reticulum.