Mitochondrion (pl.mitochondria)is the site of aerobic resiration. Mitochondria have a highly folded innet membrane which supports the proteins of the electron transport chain responsible for the synthesis of ATP by oxidative phosphoryation. The mitochondrial matrix contains the enzymes of the TCA cycle,an important metabonic 'hub'. These organelles are abundant in cells which are physically (skeletal muacle) and metabolically (hepatocytes) active.