Oxygen is used and CO2 is produced by the process of metabolism throughout the body. The lungs are just an area of exchange. In your lungs blood cells pick up oxygen to take to all the tissues of your body from your brain to your the skin on your toes. Meanwhile the blood returning from that tissue releases the carbon dioxide it picked up from the tissue and releases it into the lung where you exhale it into the atmoshpere.
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Answers
Oxygen is used and CO2 is produced by the process of metabolism throughout the body. The lungs are just an area of exchange. In your lungs blood cells pick up oxygen to take to all the tissues of your body from your brain to your the skin on your toes. Meanwhile the blood returning from that tissue releases the carbon dioxide it picked up from the tissue and releases it into the lung where you exhale it into the atmoshpere.