i think the answer you're looking for is the lungs or alveoli
Explanation:
During gas exchange oxygen moves from the lungs to the bloodstream. At the same time carbon dioxide passes from the blood to the lungs. This happens in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli. I need a bit more of the question or unit for context but i hope this helped.
