You cannot show how the body repairs itself during sleep, but get students to measure their height as soon as they get up in the morning and then again just before they go to bed. They should find they are slightly shorter in the evening because the body compresses the soft discs between the bones of the backbone during the day.

Try taking students’ pulse rates when they have been at rest on the floor for about five minutes, and compare this with rates taken while they are walking or doing gentle exercise. You could take the pulse after drinking coffee or cola (or other caffeine-containing drinks), to find out how the drug affects the body.