Keystone Biology Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

Mitochondria are often referred to as the "powerhouses" of the cell because one of their main functions is cellular respiration. This process involves breaking down glucose and other molecules to produce adenosine triphosphate (ATP), which is the energy currency of the cell. During cellular respiration, mitochondria convert the chemical energy stored in food into energy that the cell can use.

The process occurs in several stages, including glycolysis, the citric acid cycle, and oxidative phosphorylation, with mitochondria playing a critical role in generating ATP through the latter stages. Since ATP is vital for numerous cellular processes, the mitochondrion's role in energy production is essential for the survival and functioning of eukaryotic cells.

The other functions listed involve different structures or processes. For instance, synthesizing proteins primarily occurs in ribosomes, while storage of nutrients is typically associated with vacuoles or other types of organelles. Photosynthesis is specific to chloroplasts found in plant cells and some algae, making cellular respiration the main function of the mitochondrion in energy metabolism.