Final answer:
The rough endoplasmic reticulum is named for its rough appearance due to ribosomes on its surface, which synthesize proteins for export or delivery within the cell.
Step-by-step explanation:
The rough endoplasmic reticulum (RER) is so named because it has ribosomes attached to its cytoplasmic surface. These ribosomes are responsible for protein synthesis and give the RER a studded, or 'rough,' appearance when viewed under an electron microscope. The RER functions in the transport of materials through the cell and in the synthesis of proteins that are either destined for export from the cell, incorporation into the cell's membrane, or delivery to other organelles. The membrane of the RER is also continuous with the outer nuclear envelope. In contrast, the smooth endoplasmic reticulum (SER) lacks ribosomes and thus has a smooth appearance.