Onion Cell Structure

(Middle School/High School)

What will students learn?

By observing onion cells under a microscope, students will learn about the basic principles of microscopy, develop skills in slide preparation, and gain insights into the structure of plant cells. This hands-on activity provides a practical understanding of cell morphology, the presence of cell walls, and the identification of cellular components such as nuclei.

What do you need?

  • Onion Bulb

  • Microscope

  • Microscope Slides and Coverslips

  • Dropper or Pipette

  • Staining Solution (optional)

  • Tweezers

Steps:

  • An onion is composed of layers separated by a thin membrane. For this experiment, the thin membrane will be utilized to observe onion cells.

  • Use tweezers to carefully peel off the thin membrane from any layer of the onion. This membrane will serve as the specimen for observation.

  • Add a drop of water on the microscope slide and delicately place the thin membrane on the slide.

  • If needed, add more drops of water on the onion peel to prevent it from drying out during observation. If you're using a staining solution, add a drop of it to the peel. Iodine is commonly used as it stains the cell components.

  • Gently place a coverslip over the onion peel. Ensure there are no air bubbles trapped.

  • Turn on the microscope and place the prepared slide on the stage.

  • Start with the lowest magnification objective lens (usually 4x or 10x) and bring the specimen into focus using the coarse and fine adjustment knobs.

  • Gradually increase the magnification using higher objective lenses (40x, 100x).

  • Observe the onion cells. You should be able to see rectangular cells with distinct cell walls. Look for the cell nucleus, which may appear as a darker spot within the cell.