Answer:
When we breathe in through our nose and mouth, the lungs bring in air and then oxygen into our blood, in our lungs there are billions of tiny sacs called the alveoli, it has a huge surface area and the walls are extremely thin, this is when the air in the lungs travels to get to the blood in the capillaries, which it is very small in the body's blood vessels, and it is a part of the microcirculation. The blood is oxygenated, which is carried by red blood cells; this then travels to the heart into the right atrium and down the right ventricle. The oxygenated blood then travels around the whole body to get rid of the waste product; this is known as respiration. When the respiration takes place the oxygenated blood uses energy to turn into carbon dioxide, which is the waste product. When the waste product is being removed, it is carrying out CO2, so this means the oxygenated blood turns in de-oxygenated blood. The de-oxygenated gets pumped through the left atrium, up to the left ventricle, through are lungs and then we breathe out the carbon dioxide; this is known as the gaseous exchange of oxygen into carbon dioxide.