Why is the mitochondria called the powerhouse of the cell?

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). Cells can produce two ATP by breaking down a glycogen molecule, but the mitochondria is able to produce up to 36 ATP in comparison.

Glycolysis, the process where glycogen is converted into energy, takes place in the cell's cytoplasm. It produces two ATP per glycogen molecule and pyruvate as a waste product. After transporting pyruvate into the cell's mitochondria, it begins the Krebs Cycle, which is a serious of steps that produces between 34 and 36 ATP.