Make and stain a temporary slide sim

What the sim shows

A light microscope on the bench, a clean glass slide on a white tile, three dropping bottles (distilled water, iodine solution, methylene blue), half an onion with forceps, a cotton bud, a box of 22 mm coverslips with a mounted needle, and paper towel. A temporary slide holds a thin specimen in liquid under a coverslip. Onion epidermis: peel the thin skin from the inner surface of an onion scale with forceps and lay it flat in a drop of water, then add iodine solution, which stains the nuclei and cytoplasm yellow-brown (and starch blue-black; onion epidermis has little starch). Cheek cells: rub a clean cotton bud gently inside your own cheek, smear it on the slide and add methylene blue, which stains the nuclei blue. Cells are thin and almost colourless, so without a stain they are nearly invisible. Then touch one edge of the coverslip to the liquid at about 45° and lower it slowly with the mounted needle: the liquid runs along the edge and pushes the air out ahead of it. A coverslip put down flat, or let fall, shuts in air bubbles, which show as circles with thick black rims. Blot the extra liquid from the edge with paper towel, and look under low power first, then high power. Model: one drop is 0.05 cm³ (50 mm³); a 22 mm coverslip holds a film up to 0.15 mm deep, 72.6 mm³ or 1.45 drops, so a second drop runs out past its edges. Bubbles: none at a contact angle of 40° or more lowered slowly; one for every 7° short of 40°; four or more below 20°; 2 more if lowered faster than 90°/s and 3 more if the needle lets go above 10° (illustrative counts). The close-up shows 800 µm across at ×100 and 200 µm at ×400; onion cells are drawn 250 × 50 µm, cheek cells 55 µm across.

• Each tool: drag it to the slide (one action = one step)
• The coverslip: the height of its free edge sets the angle; the needle lowers it
• Iodine solution is orange-brown; methylene blue stains nuclei blue

Use it in your lessons

• Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
• Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
• Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.

Free guide: 12 practicals as sims, and how to run one in a lesson →

Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.