What is the main function of mitochondria in a cell?

Mitochondria are often referred to as the "powerhouses" of the cell because their primary role is energy production. They accomplish this through a process known as cellular respiration, which converts biochemical energy from nutrients into adenosine triphosphate (ATP), the energy currency of the cell. This process occurs in several stages, primarily in the mitochondria's inner membrane, where the electron transport chain and ATP synthase operate to generate ATP. Mitochondria play a crucial role in not only providing energy but also in regulating metabolic processes and apoptosis (programmed cell death).

The other options describe functions that are not performed by mitochondria. Protein synthesis occurs mainly in ribosomes, either freely floating in the cytoplasm or attached to the endoplasmic reticulum. Cell division is primarily managed by structures such as the nucleus and the mitotic spindle. Photosynthesis is a process carried out in chloroplasts, which are unique to plant cells, allowing them to convert light energy into chemical energy.