Final answer:
The mitochondria's function in a cell is to perform cellular respiration, producing ATP, the cell's primary energy-carrying molecule.
Step-by-step explanation:
The function of the mitochondria in a cell is cellular respiration. Mitochondria are known as the "powerhouses" or "energy factories" of a cell because their primary role is to produce adenosine triphosphate (ATP), which is the main molecule carrying energy within the cell. The process of transforming the chemical energy found in glucose into ATP is called cellular respiration, which involves the consumption of oxygen and results in the production of carbon dioxide as a byproduct.