Magnifying and Observing Cells
Comparing Onion and Elodea Cells
Guide students as they observe the cells. Ask questions that will encourage them to look at relative sizes and shapes of cells. Help students to identify visible structures: cell walls in both kinds of cells; chloroplasts in Elodea leaf; and nuclei (one per cell) in onion epidermis.
Cell nuclei usually are easy to observe in the onion samples, but they will not be visible in all cells. Students also may notice one or more vacuoles within the onion cell cytoplasm, and tiny perforations, or pits, in the onion cell walls that connect the cytoplasm of adjacent cells. Nuclei are much less visible in the Elodea cells, which have abundant green chloroplasts.
Encourage students to make detailed drawings of their observations. Also, have students use the fine focus knob of the microscope to focus down through the layers of cells. Ask students to think about whether cells are flat or three-dimensional structures.
The cell membrane in Elodea cells can be observed if a sample is prepared in a drop of salt water. The movement of water out of the cell in the presence of saline solution will cause the cell membrane (also called plasma membrane or plasmalemma) to pull away slightly from the cell wall.
- Moreno, N., Tharp, B., Erdmann, D., Rahmati Clayton, S., Denk, J. (2008). The Science of Microbes Teacher’s Guide. Houston, TX: BioEd.
- Walsh, J. Cells in Elodea leaf, showing plastids, elodea00. Micrographia, www.micrographia.com.
- Walsh, J. Onion epidermis. Micrographia, www.micrographia.com.
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Grant Number: 5R25RR018605