Mitochondria play a critical role in metabolism, often referred to as the "powerhouses" of the cell. They are responsible for converting nutrients from food into usable energy in the form of adenosine triphosphate (ATP) through a process called cellular respiration. This involves breaking down glucose and fatty acids in the presence of oxygen. Mitochondria also regulate other metabolic pathways, including the synthesis of certain hormones and the maintenance of cellular energy homeostasis, making them vital for the overall functioning of living organisms.