Differences in Inspired & Expired Air (Cambridge (CIE) IGCSE Biology): Revision Note

Differences in inspired & expired air

• Air that is inhaled, or breathed in, differs in its gas composition to air that is exhaled, or breathed out; this is due to the process of gas exchange that takes place in the alveoli

  • Inhaled air can also be referred to as inspired air

  • Exhaled air is also known as expired air

• Inhaled air is drawn from the surrounding atmosphere, and so its gas composition matches atmospheric levels

• During gas exchange in the alveoli oxygen enters the blood from the alveoli, and carbon dioxide and water vapour leave the blood and enter the alveoli

• This gas exchange process means that the gas composition of exhaled air differs to that of the air that was previously inhaled 

  • Inhaled air contains around 21 % oxygen and exhaled air contains around 16 % oxygen

  • Inhaled air contains around 0.04 % carbon dioxide and exhaled air contains around 4 % carbon dioxide

  • Inhaled air contains less water vapour than exhaled air

Composition of inhaled and exhaled air table