Investigating the Differences in Inspired & Expired Air (Cambridge International IGCSE Biology)

Spec point — 11.1.3 · Investigate the differences in composition between inspired and expired air using limewater as a test for carbon dioxide

Investigating the differences in inspired & expired air

• A simple experimental setup can be used to investigate the differences between inspired and expired air

The limewater test

• When air is breathed in, it is drawn through boiling tube A

• When air is breathed out, the air is blown into boiling tube B

• Limewater is clear but becomes cloudy (or milky) when carbon dioxide is bubbled through it

  • The limewater in boiling tube A will remain clear, as inhaled air is atmospheric air, which contains a very low percentage of carbon dioxide The limewater in boiling tube B will become cloudy, as exhaled air has passed through the lungs (where gas exchange has taken place) and contains a higher percentage of carbon dioxide

• This shows us that the percentage of carbon dioxide in exhaled air is higher than in inhaled air