Many people were taught in school that the mitochondria are those little organelles that act as the powerhouses in our cells. Besides playing a key role in bioenergetics like ATP production, mitochondria are also responsible for glycolysis (the metabolic pathway that converts food into pyruvate) and cellular respiration (transfer of protons and electrons to create ATP), and the number of mitochondria in each cell can range from a few to thousands per cell depending on factors like age, nutrition, and exercise.