Breathing, respiration and gas exchange

Humans and other animals breathe to move air in and out of their lungs. Cells need oxygen from the air for cellular respiration, to provide energy for life processes. Cellular respiration produces carbon dioxide as a waste product. Oxygen needs to be absorbed into, and carbon dioxide needs to be removed from, the human body. In gas exchange, oxygen diffuses from the lungs into the blood; carbon dioxide diffuses from the blood into the lungs.