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

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 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