Answer:
Rough endoplasmic reticulum looks "rough" under a microscope because it has ribosomes attached to its surface.
Step-by-step explanation:
Rough endoplasmic reticulum (RER) is a membrane organelle found in the cytoplasm of eukaryotic cells, which has ribosomes attached to its outer surface. Hence the name, rough endoplasmic reticulum. It has an important role in the synthesis of proteins. In ribosomes, the proteins are synthesized. The smooth endoplasmic reticulum (SER) does not contain ribosomes. It has an impotant role in the synthesis and storage of lipids. The proteins that are synthesized in the ribosomes are packaged into vesicles and transported to the Golgi apparatus by the rough endoplasmic reticulum. The Golgi apparatus which is located near the RER, modifies, transports and packages proteins for delivery to targeted destinations.