The mitochondria is called the powerhouse of the cell because it is responsible for producing most of the cell's energy, or adenosine tri-phosphate (ATP). Mitochondria are able to multiply in... The mitochondria is called the powerhouse of the cell because it is responsible for producing most of the cell's energy, or adenosine tri-phosphate (ATP). Mitochondria are able to multiply in response to the energy needs of a cell, so that cells requiring more energy to function are powered by more mitochondria than cells with lower energy needs.