The primary gas released during respiration is carbon dioxide (CO2). During this biochemical process, living organisms—including animals and humans—convert glucose and oxygen into energy. This reaction occurs primarily in the mitochondria of cells, where glucose, derived from food, is oxidized, resulting in ATP (adenosine triphosphate) as the energy currency of the cell. As a byproduct, carbon dioxide is formed and subsequently expelled from the organism through the lungs or other excretory systems. This gas plays a critical role in the carbon cycle, influencing both environmental and physiological processes.