The cellular structure that produces ATP is the mitochondrion. Often referred to as the "powerhouse of the cell," mitochondria are responsible for converting the energy stored in glucose and other nutrients into adenosine triphosphate (ATP) through the process of cellular respiration. This energy is then used by cells to perform various functions, including muscle contraction, nerve impulse transmission, and metabolic processes. Mitochondria also play roles in regulating apoptosis and cellular metabolism, underscoring their vital importance in cellular health and energy management.