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