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Even larger human cells - like the skin cell - are 20 times smaller than a grain of salt. A red blood cell is much smaller than that.

To allow us to see detail in these cells, we need the help of a microscope.

Making slides

A slide is a thin piece of glass used to hold objects which are examined under a microscope.

Most slides will already be made up for you. If you do get the chance to prepare your own slide, here’s what to do:

Plant cells

1. Peel a thin, transparent layer of epidermal cells from the inside of an onion.
2. Place cells on a microscope slide.
3. Add a drop of water or iodine (a chemical stain).
4. Lower a coverslip onto the onion cells using forceps or a mounted needle. This needs to be done gently to prevent trapping air bubbles.

Animal cells

1. Remove cells from the inside of your cheek using a cotton bud.
2. Smear the cotton bud onto a microscope slide.
3. Add a drop of methylene blue (a chemical stain).
4. Lower a coverslip onto the cheek cells using forceps or a mounted needle. This needs to be done gently to prevent trapping air bubbles.

Chemical stains are used to make some cell parts more obvious.