Differences in Inspired & Expired Air (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

• Air that is breathed in and air that is breathed out has different amounts of gases in it due to exchanges that take place in the alveoli
• Atmospheric air contains around 20 – 21% oxygen, of which we only absorb around 4 – 5%, expired air contains around 16% oxygen
• Normal carbon dioxide content of air is around 0.04% and, as carbon dioxide diffuses into the alveoli from the blood, we expire air containing around 4% carbon dioxide
• The air we breathe out contains more water vapour (around 1%) than when we breathe it in which is variable
• The temperature of exhaled air is higher than inhaled air due to heat energy released from respiration

Composition of Air Table