What is the main purpose of mitochondria in cells?

Mitochondria are often referred to as the "powerhouses" of the cell because their primary function is energy production. They are responsible for converting nutrients into adenosine triphosphate (ATP), the energy currency of the cell, through a process known as cellular respiration. This process involves the breakdown of glucose and other substrates, and it generates ATP along with carbon dioxide and water as byproducts.

Mitochondria are integral to numerous metabolic processes, including the Krebs cycle and oxidative phosphorylation, which are key steps in energy production. This energy is critical for sustaining cellular functions, such as muscle contraction, biochemical synthesis, and maintaining cellular health. The efficient energy production by mitochondria supports the overall physiological activities of the organism.

In contrast, options related to waste removal, protein digestion, and cell division describe functions that involve other cellular structures or processes rather than the main role of mitochondria. For instance, lysosomes play a key role in waste removal and protein digestion, while the processes of cell division involve the nucleus and other components like the mitotic spindle.