The cells in the body need oxygen to release energy from food efficiently by carrying out aerobic respiration. A waste product of aerobic respiration is carbon dioxide. The layer of moisture in the ...

Easy breathing depends on the millions of delicate, air-filled sacs, known as alveoli, that are the site of gaseous exchange in the lungs. Each alveolus is composed of two distinct epithelial cell ...

We need to get oxygen from the air into the blood, and we need to remove waste carbon dioxide from the blood into the air. Moving gases like this is called gas exchange. As the blood moves through the ...