The primary gas produced during cellular respiration is carbon dioxide (CO2). This process occurs in the mitochondria of cells, where glucose and oxygen are converted into energy (ATP). As glucose undergoes oxidation, carbon dioxide is released as a byproduct, which cells then expel into the bloodstream. The removal of carbon dioxide is essential for maintaining proper pH levels in the body and ensuring that metabolic processes can continue efficiently. Overall, the production and expulsion of CO2 are crucial components of metabolic homeostasis.