This activity is one of the first uses of an optical microscope that most school children encounter in a school biology lab. Onions are used because they have large cells that are easily visible under a student microscope. This experiment is normally performed by children between the ages of 11 and 14.
An onion is made of many concentric layers. Each layer is separated by a thin skin or membrane. In this experiment you will make a slide and look at the cells of the membrane under a microscope.