Mitochondria consist of double membranes and cristae that are infoldings of the inner membrane. On the cristae is where sugar is combined with oxygen to create ATP which is the primary energy source of the cell. The primary function of mitochondria is to provide the energy a cell needs to move, divide, produce secretory products, and contract. Mitochondria are large enough to be seen under a light microscope, having a size just greater than about 1μm. Under an electron microscope, mitochondria appear as lines of cristae parallel to each other inside a grey oval with a double membrane.