The main function of mitochondria in cells is to produce adenosine triphosphate (ATP), which serves as the primary energy currency of the cell. Often referred to as the "powerhouses" of the cell, mitochondria facilitate cellular respiration, a process that converts biochemical energy from nutrients into ATP. This energy is then used for various cellular functions, including growth, maintenance, and division. Mitochondria also play roles in regulating metabolic activities and programmed cell death, highlighting their crucial importance in cellular biology.