The gas produced as a waste product of respiration is carbon dioxide (CO2). During respiration, cells take in oxygen to convert glucose into energy through a biochemical process called cellular respiration. This process generates energy and produces carbon dioxide as a byproduct, which is then transported back to the lungs to be exhaled. This exchange of gases—oxygen being inhaled and carbon dioxide exhaled—is crucial for maintaining the balance of gases in the atmosphere and is fundamental to life on Earth.