Onion cells under a microscope

In this post I will show how to make a wet-mount slide for looking at onion cells under a microscope.

Making the slide

1. Take a clean slide and place a drop of water in the centre.
2. Take a small piece of onion and carefully peel the translucent membrane from the rough underside. To peel the membrane, use either a sharp blade or a pair of tweezers. It is important to do this step carefully so as not to break too many cells — ideally hold the peeled membrane at the edges.
3. Carefully place the membrane in the drop of water on the slide.
4. Optionally, place a small drop of tincture of iodine over the onion membrane. This helps create contrast between cell nuclei and the rest of the cell.
5. Gently lower a cover slip over the membrane.

Micrographs

The nuclei are the small dark circles and the thick black lines are the cell walls.

Onion cells magnified 40 times.

Onion cells magnified 100 times.