Breathing is all about gas exchange. Oxygen is taken from the air and enters the red blood cells for transport around the body. At the same time, carbon dioxide is removed from the blood and excreted in the air that we breathe out.

A common experiment looks at the difference in composition of inhaled and exhaled air. In the school science laboratory, you may have used the suck and blow equipment shown in the diagram.

As you breathe in through the mouthpiece, air is drawn in through a solution of limewater. This tests to see how much carbon dioxide is in the inhaled air. There is a very small amount of carbon dioxide but it would take a long time for the inhaled air to turn the limewater milky.

The exhaled air is also bubbled through limewater. This turns milky very quickly and indicates that there is a lot of carbon dioxide in the air breathed out.

The suck and blow apparatus does not measure the actual amounts of carbon dioxide in exhaled and inhaled air. It also will not give any information on the levels of oxygen, nitrogen and water vapour or the speed and depth of breathing. In exercise physiology laboratories more complex equipment is used to measure exactly the composition of gases in the inhaled and exhaled air. This gives a lot more information on the rate of respiration and how efficiently the lungs are working. Many professional sportspeople will regularly have their fitness monitored using this type of equipment.

Check the type of results that would be expected when gas analysis is carried out.