How to prepare an onion cell slide
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.
- Take a small piece of onion and using forceps (tweezers) peel off the membrane from the underside (the rough side).
- Lay the membrane flat on the surface of a clean glass slide, and then add one drop of dye (iodine or methylene blue). Be very careful; these dyes will stain your skin and clothes.
- Using a pin, lower a thin glass cover slip onto the slide. Make sure there are no air bubbles.
- Put the slide onto the stage of the microscope. Make sure the objective lens is set on low power, and the microscope light is turned on.
- Look through the eyepiece lens and turn the focusing wheel until you can see the cells. They should look like lizard skin.
- Swap the objective lens for a high powered one so that you can see the cells at a greater magnification. You should be able to make out the nucleus.