Final answer:
The rough endoplasmic reticulum (RER) with ribosomes along its length transports many proteins in the cell.
Step-by-step explanation:
The correct answer is a. Endoplasmic reticulum (ER). The rough endoplasmic reticulum (RER) is characterized by the presence of ribosomes along its surface. It is responsible for the synthesis and transport of many proteins in the cell.
The ribosomes on the RER produce proteins, which are then transported in small sacs called transport vesicles to their proper destinations in the cell. Examples of proteins that are synthesized and transported by the RER include enzymes, hormones, and structural proteins that are needed for various cellular functions.