Final answer:
Mitochondria are the organelles in cells that convert chemical energy from nutrients into ATP through cellular respiration, thus providing energy for the cell.
Step-by-step explanation:
The function of mitochondria is primarily to act as the "powerhouses" or "energy factories" of the cell, an organelle where cellular respiration takes place. Within the mitochondria, biochemical reactions transform chemical energy found in nutrients into adenosine triphosphate (ATP), which provides usable energy to the cell. This process of making ATP is known as cellular respiration, involving oxygen and producing carbon dioxide as a waste product, which is exhaled. Therefore, the correct answer to the student's question is C. Organelle in charge of breaking down chemical energy into ATP and heat.