2. The structure and functions of Endoplasmic Reticulum(Er) (a)Rough endoplasmic reticulum 0.5 um (b)Smooth endoplasmic reticulum 0.5m Figure 12-2 Rough and Smooth Endoplasmic Reticulum studded with ribosomes (TEM).(b)Electron micrograph of smooth la) Electron micrograph of endoplasmic reticulum. The rough ER is endoplasmic reticulum(TEM) RER has ribosomes on the cytosolic side of continuous, flattened sacs(cisternae) SER is an interconnecting network of tubular membrane elements Rough endoplasmic reticulum and Smooth endoplasmic reticulum2. The structure and functions of Endoplasmic Reticulum(ER) Rough endoplasmic reticulum and Smooth endoplasmic reticulum RER has ribosomes on the cytosolic side of continuous, flattened sacs(cisternae); SER is an interconnecting network of tubular membrane elements