Measuring respiration

Respiration by living organisms can be investigated by carrying out experiments to show the production of carbon dioxide.

A respiration experiment using limewater in a test tube. Step 1: A pipe labelled carbon dioxide gas enters the test tube, there are bubbles in the limewater. Step 2: the limewater turns milky.

If carbon dioxide is bubbled through limewater then it turns from clear to cloudy/milky in colour. This is why limewater used in a simple respirometer can show that more carbon dioxide is present in exhaled air compared to inhaled air.

Using a respirometer

Experiment to detect the production of carbon dioxide, using a respirometer.

Breathing in through the mouthpiece draws air from the atmosphere in through tube A. Breathing out through the mouthpiece bubbles exhaled air through tube B. After a few breaths the limewater in tube B will turn cloudy as the exhaled air contains more carbon dioxide.


If inhaled air contains 0.04% carbon dioxide and exhaled air 4%, how many times more carbon dioxide do you breathe out than you breathe in?

100 times more.