Mitochondria. Coloured transmission electron micrograph (TEM) of mitochondria (blue) from a kidney tubule. Mitochondria are organelles found in the cytoplasm of eukaryotic cells. They oxidise sugar and fats to produce energy. Mitochondria have two membranes, a smooth outer membrane and a folded inner membrane. The folds of the inner membrane are called cristae, and it is here that the chemical reactions to produce energy take place. Magnification: 10, 000 x when printed 10 centimetres wide.