Onion Root Tip Preparation

Understanding intangible concepts can be difficult for students, especially when they have little chance of observing those concepts in real time. However, science labs can help students visualize the concepts and retain information. For instance, cell division involves many steps of development that students may have trouble understanding. Help them visualize each step by creating onion root tip slides. As onion roots develop, you can prepare slides that catch the cells dividing and let your students observe them.

Seed trays
Vermiculite
Pearl onions
Distilled water
Razor blades
Glass slides
Feulgen stain (purple stain)
Slide covers
Microscopes

Instructions

- 1
  Add about ¾ inch of vermiculite to several seed trays. Scatter pearl onions on top of the vermiculite and cover them. Water the onions until the vermiculite is fully saturated.
- 2
  Place the seed trays in a warm, sunny area for about a week. They should sprout roots within several days. As the roots grow, cells divide and reproduce constantly.
- 3
  Remove the onions from the soil and rinse them well under distilled water. Slice the roots from each onion. You may replant the onions for other experiments or discard them.
- 4
  Gently scrape the onion root tips with a sharp razor blade, removing very thin layers of tissue. Gently grip the tissue and slip it over the tip of your finger.
- 5
  Press the tip of your finger to the center of a glass slide and roll it from right to left, leaving the onion root tip on the slide.
- 6
  Drip a drop or two of Feulgen stain onto the root tip sample. Drop a slide cover over the sample and press down with a fingertip, sealing it to the slide.
- 7
  Slip the slide under a microscope to see if you can identify the stage of cell division you see.

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