Rough endoplasmic reticulum (RER), transmission electron micrograph (TEM). RER is a subcellular organelle studded with ribosomes (black dots). The RER produces and processes specific proteins that are then exported through the secretory pathway of the cell via membrane vesicles where they can then be further processed or sent to other organelles. These proteins can also be exported outside the cell. Magnification: x9000 when printed at 10 cm wide.