Answer:
Ribosomes
Step-by-step explanation:
The endoplasmic reticulum is a network of interconnected sacs and tubules distributed throughout the cytosol. There are two types of endoplasmic reticulum: smooth endoplasmic reticulum and rough endoplasmic reticulum. The rough endoplasmic reticulum is the one that has ribosomes studded on its outer surface. The presence of ribosomes gives the rough endoplasmic reticulum a rough appearance.
On the other hand, the smooth endoplasmic reticulum has a smooth outer surface due to the absence of ribosomes on it. The main function of rough endoplasmic reticulum is protein synthesis as ribosomes are the site for protein synthesis. The smooth endoplasmic reticulum is involved in lipid biosynthesis.