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Safe Food Preparation

Author(s): Nancy Moreno, PhD, Barbara Tharp, MS, and Judith Dresden, MS.
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Preparing Wet Mount Slides of Plant Cells

Have students follow the instructions on the cards provided to prepare slides with wet mounts of onion and Elodea tissue. On its inner surface, each section of onion has a thin sheet of skin that is easy to peel off. Deeper layers are far more difficult to remove as a single sheet. Students will use iodine to stain the onion skin cells, so that the somewhat transparent cells and nuclei are easier to observe. Remember to review safety precautions when using iodine. Certain people are allergic to iodine. It will not be necessary to stain the Elodea cells.

The onion tissue will not have chloroplasts. This absence could be predicted from the lack of green coloration. The onion itself is a bulb, comprised of the bases of overlapping leaves that originate at the bottom of the plant. 

Technically, an onion is a specialized stem, not a root. The onion "skin" that students will observe is the epidermis of the overlapping leaf bases. If students have questions about the structure of an onion, show them a scallion or green onion with the leaves attached.

Funded by the following grant(s)

National Institute of Environmental Health Sciences, NIH

National Institute of Environmental Health Sciences, NIH

My Health My World: National Dissemination
Grant Number: 5R25ES009259
The Environment as a Context for Opportunities in Schools
Grant Number: 5R25ES010698, R25ES06932