Mitochondria. Coloured scanning electron micrograph (SEM) of mitochondria (pink) in a kidney cell. Mitochondria are a type of organelle found in the cytoplasm of eukaryotic cells. They oxidise sugars and fats to produce energy in a process called respiration. A mitochondrion has 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. The purple structures seen here are the cell membranes of the kidney cells.