Mitochondria are often called the “powerhouses” or “energy factories” of a cell because they are responsible for making adenosine triphosphate (ATP), the cell's main energy-carrying molecule. Mitochondria are tiny double membrane-bound organelles found in almost every cell of all organisms except bacteria. Known as the “powerhouse of the cell” they are primarily responsible for converting the air we breathe and the food we eat into energy that our cells can use to grow, divide and function. Mitochondria are tiny organelles inside cells that are involved in releasing energy from food. This process is known as cellular respiration. It is for this reason that mitochondria are often referred to as the powerhouses of the cell.