The main function of the respiratory system is gaseous exchange. This is the process of oxygen and carbon dioxide moving between the lungs and blood.
Diffusion occurs when molecules move from an area of high concentration to an area of low concentration, this occurs during gaseous exchange, as blood in the capillaries which surround the alveoli has lower concentration compared to the air in the alveoli which has just been inhaled.
The alveoli and capillary walls are only one cell thick to allow gases to diffuse across them. It is the same for carbon dioxide. The blood in the surrounding capillaries has a higher concentration of CO2 than the air you have just inhaled and this CO2 which has already travelled around the body is ready to become a waste product. Whereas CO2 diffuses the other way, from the capillaries, into the alveoli where it can be exhaled.
' The air we breath contains approximately 21% oxygen and 0.04% CO2. When we exhale there is approximately 17% oxygen and 3% CO2.' This shows a decrease in oxygen levels as it is used in producing energy and increases the CO2 due to it being a waste product of energy production.
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