The gas produced as a byproduct of respiration is carbon dioxide (CO2). When organisms, including humans, metabolize food for energy, oxygen is used to break down glucose, resulting in the release of carbon dioxide as a waste product. This process occurs in the cells during cellular respiration, where energy is generated in the form of adenosine triphosphate (ATP). After carbon dioxide is produced, it is transported back to the lungs, where it is subsequently exhaled. The balance of carbon dioxide and oxygen is crucial for maintaining healthy biological functions and ecosystems.