Students prepare a microscope slide using a thin layer of onion epidermis, stain it with food coloring or iodine, and observe the cell structures such as the cell wall, nucleus, and cytoplasm under different magnifications.

1. Cut an onion in half and carefully peel away a very thin, transparent layer of epidermis.
2. Place the onion layer flat onto a clean glass slide.
3. Gently lower a cover slip over the sample.
4. Add a drop of food coloring or iodine at the edge of the cover slip and allow it to soak under by capillary action.
5. Place the slide on the microscope stage and secure it with clips.
6. Begin viewing with the lowest power objective lens, adjusting the coarse focus until the cells come into view.
7. Switch to a higher power lens and use the fine focus to clearly see the details of the onion cells.

Onion Skin Epidermal Cells: How to Prepare a Wet Mount Microscope Slide - Tami Guy, MS, CPPS:

ONION CELLS VIDEO - Elizabeth Godwin:

📄 How to observe cells under a microscope - BBC Bitesize: https://www.bbc.co.uk/bitesize/articles/zbm48mn#zm33f82

• Compare onion epidermis with cheek cells to highlight differences between plant and animal cells.
• Use different stains (methylene blue) to emphasize various cell parts.
• Try preparing slides from different vegetables (garlic, celery) for comparison.

• Use caution when handling sharp knives to cut the onion; ask for adult supervision if needed.
• Handle glass slides and cover slips carefully to avoid cuts.
• Wash hands thoroughly after handling onions and stains.
• Avoid getting stains on clothing or skin.

• What structures are clearly visible in onion cells that are not seen in cheek cells? (cell wall, sometimes a large vacuole, and rectangular cell shape)
• Why is onion epidermis suitable for observing plant cells? (it is thin, transparent, and made of a single layer of cells)
• What role does staining play in observing onion cells? (stains make the nucleus and cytoplasm more visible)
• How does increasing magnification change the detail observed in onion cells? (it allows visualization of smaller structures but reduces the visible area of the sample)