The presence of ribosomes on the roughER suggests that the proteins are synthesized as well as modified there as opposed to the smooth ER.
Ribosomes are responsible for the synthesis of proteins from the amino acids. They translate each codon on the RNA template and match it with the appropriate amino acid to make a protein. This process is known as translation. Ribosomes can be found free in the cytosol or attached to the surface of the endoplasmic reticulum. When the ribosomes are bound to it, it is known as the rough ER and without it, it is called smooth ER. Smooth ER performs different functions like the synthesis of lipids and phospholipids. Since it does not have ribosomes, it cannot synthesize proteins.
