The powerhouse cell is the mitochondrion. Mitochondria are the organelles that are responsible for the production of energy in the cell. They are often called the "powerhouse of the cell" because they are responsible for generating the ATP (adenosine triphosphate) that the cell needs to function. ATP is the primary source of energy for cells and is essential for many cellular processes, including metabolism, growth, and movement. Mitochondria are small, bean-shaped organelles that are found in the cytoplasm of cells. They are made up of two membranes: an outer membrane and an inner membrane. The inner membrane is folded into cristae, which are shelf-like structures that increase the surface area of the membrane and provide a place for the electron transport chain to occur. The electron transport chain is a series of proteins that pass electrons from one protein to the next, releasing energy in the form of ATP.