The lungs hold air that is breathed in. Oxygen gas in the air moves into the blood. The heart pumps to transports this oxygenated blood to cells in the body that need it to produce energy. Hope This Helps! :)
Carbon dioxide is produced when the muscles use up oxygen and absorbed into the blood, the blood carries the CO2 into the heart which in turn pumps it into the lungs. Lungs get rid of carbon dioxide and re-oxygenate the blood.
