Rough endoplasmic reticulum and mitochondria. Coloured transmission electron micrograph of mitochondria (red circles) and rough endoplasmic reticulum in a liver cell. Mitochondria oxidize sugars and fats to supply the cell with energy. They are bound by a double membrane and contain numerous folded membranes called cristae, where respiration takes place. The endoplasmic reticulum (ER) is a network of membranes (yellow) that divides the cell into compartments. Rough ER is studded with protein-manufacturing bodies called ribosomes. Magnification x13,700 at 6x4.5cm size.