How to prepare an onion cell slide
This activity is one of the first uses of an optical microscope that most school children ever 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 - 14.
An onion is made of lots of 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.
- 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 then add 1 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[?] over 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 bigger magnification.You should be able to make out the nucleus.