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
• The 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
• Limewater test - a simple experimental setup can be used to investigate the differences between inspired and expired air

  A) mouth

  B) rubber tubings

  C) boiling tubes

  D) lime water

  
• The limewater test

  • When we breathe in, the air is drawn through boiling tube A
  • When we breathe out, the air is blown into boiling tube B
  • Lime water is clear but becomes cloudy (or milky) when carbon dioxide is bubbled through it
  • The lime water in boiling tube A will remain clear, but the limewater in boiling tube B will become cloudy
  • This shows us that the percentage of carbon dioxide in exhaled air is higher than in inhaled air