Pupils know from experience that drops of liquid act as lenses. They may have sneezed near a computer screen and seen pixels magnified by the water droplets.

Challenge pupils to make a simple “microscope” using a drop of liquid from a pipette and keep it in place for viewing. Bent paper clips and holes of various sizes in card and plastic can be used.

Pupils will note a problem using a water drop: it soaks into the card after falling from the paper clip, and the small hole makes viewing very difficult water is too runny.

Provide a range of more viscous liquids such as olive oil, washing up liquid and glycerine.

A 2mm drop of glycerine on a strip of clear plastic works well, and magnifies about five times. Two lenses, one above the other, make a more powerful compound “microscope”

Useful book: Micrographia by Robert Hook, who first used the word “cells”.

Julian Silverton teaches life science at the American Community School in Cobham, Surrey

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