Each mitochondrion is a double membrane-bound structure with the outer membrane and the inner membrane dividing its lumen distinctly into two aqueous compartments, i.e., the outer compartment and the inner compartment. The inner compartment is filled with fluid called matrix. The inner membrane forms a number of infoldings called the cristae. Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called ‘power houses’ of the cell. The matrix possesses single circular DNA molecule, a few RNA molecules, ribosomes (70S) etc.