The organelle that contains the machinery for cellular respiration is the mitochondrion. It is often called the "powerhouse of the cell" because it produces the majority of ATP, the cell's energy currency, through aerobic respiration. Cellular respiration processes like the Krebs cycle occur in the mitochondrial matrix, and the electron transport chain takes place on the inner membrane's cristae. Although glycolysis occurs in the cytoplasm, the mitochondrion is the main organelle where respiration happens.