The powerhouse of the cell is the mitochondria, which is a tiny organelle inside cells that is involved in releasing energy from food through a process known as cellular respiration. Mitochondria are responsible for supplying energy to the cell, and they are often referred to as the "powerhouses of the cell". Cells that need a lot of energy, like muscle cells, can contain thousands of mitochondria. Apart from cellular respiration, mitochondria also play a key role in the aging process as well as in the onset of degenerative disease. The mitochondria is a double membrane organelle that produces molecules which are the usable form of energy for the cell. The outer membrane is porous, which means it allows the transport of materials across itself, while the inner membrane is thrown into several folds and therefore has a larger surface area.