The endoplasmic reticulum (or ER) is a set of tubular passageways in plant and animal cells that transform materials throughout the cell.  If the ER is studded with ribosomes it is called the “rough ER” and if it doesn’t have ribosomes it is called “smooth ER”  This is the postal service, which transports and moves materials. The Golgi apparatus is the company, and the ER is the service. The image on the right is the Golgi apparatus and the ER, because they work together.