The primary function of mitochondria is to produce energy through the process of oxidative phosphorylation. In this process, simpler molecules of nutrition that are sent to the mitochondria produce charged molecules. The charged molecules combine with oxygen to produce Adenosine Triphosphate (ATP), the main energy molecule used by cells.  

In addition, it also plays a key role in several other processes including: 

• Regulating the metabolic activity of the cell
• Promoting cell multiplication and the growth of new cells
• Facilitating a number of cellular activities including cell senescence, cell signaling, cellular differentiation, and regulating the cell cycle
• Ensuring that cell compartments maintain an adequate concentration of calcium ions
• Detoxifying ammonia in the liver cells
• Mediating the process of apoptosis or programmed cell death – dysfunction of mitochondria can lead to abnormal death of cells, which can adversely impact the organ’s function 
• Building certain parts of blood and hormones including estrogen and testosterone