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Wet Mount

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To make a wet mount slide, place one drop of water on a microscope slide, then position a thin sample section over the drop. Cover the sample with a coverslip at an angle like a hinge. The document also instructs to compare onion and elodea cells under a microscope by examining their size, shape, and visible structures.

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Making a Wet Mount ºÝºÝߣ Use a dropper to place one drop of water in the center of a slide. Place a small, thin section of sample on top of the drop. Place a cover slip over the sample, angling it like a hinge. BioEd Online
Comparing Onion and Elodea Cells Look for similarities or differences in: Size Shape Visible structures Elodea onion J. Walsh © Micrographia.com,www.micrographia.com BioEd Online

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Wet Mount

  • 1. Making a Wet Mount ºÝºÝߣ Use a dropper to place one drop of water in the center of a slide. Place a small, thin section of sample on top of the drop. Place a cover slip over the sample, angling it like a hinge. BioEd Online
  • 2. Comparing Onion and Elodea Cells Look for similarities or differences in: Size Shape Visible structures Elodea onion J. Walsh © Micrographia.com,www.micrographia.com BioEd Online

Editor's Notes

  • #2: Making a Wet Mount ºÝºÝߣ Have students follow these simple instructions to create wet mounts (temporary slides in which the material to be observed is placed on a drop of water and covered with a cover slip). You may want to provide iodine or methylene blue stain for students to use to make cell structures more easily visible. Iodine and methylene blue are toxic if ingested. Some people are allergic to iodine. Be certain to read the Materials Safety Data Sheets (MSDS), which should be available in the classroom during the activity. Caution: Iodine and methylene blue will stain the skin, but will gradually wash off. Both solutions will permanently stain clothing and some table surfaces. Viewing this presentation fulfills part of the requirements for completing the short course on The Science of Microbes, offered on BioEd Online for professional development contact hours. The Science of Microbes Teacher’s Guide may be obtained in its entirety from the Center for Educational Outreach, Baylor College of Medicine (1-800-798-8244). You can download a PDF of this lesson, including the pre-assessment, from www.bioedonline.org or www.K8Science.org. Reference: Moreno, N., Tharp, B., Erdmann, D., Rahmati Clayton, S., Denk, J. (2007). The Science of Microbes Teacher’s Guide. Houston, TX: BioEd. ____________________________________________________________________________ The Science of Microbes and accompanying online professional development were supported, in part, by Science Education Partnership Award number 5R25RR018605 from the National Center for Research Resources of the National Institutes of Health (NIH) to Baylor College of Medicine. The unit was developed in partnership with the Baylor-UT Houston Center for AIDS Research, an NIH-funded program (AI036211). The opinions, findings, and conclusions expressed in this presentation are solely those of the authors and do not necessarily reflect the views of Baylor College of Medicine or the sponsoring agencies.
  • #3: 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. Viewing this presentation fulfills part of the requirements for completing the short course on The Science of Microbes, offered on BioEd Online for professional development contact hours. The Science of Microbes Teacher’s Guide may be obtained in its entirety from the Center for Educational Outreach, Baylor College of Medicine (1-800-798-8244). You can download a PDF of this lesson, including the pre-assessment, from www.bioedonline.org or www.K8Science.org. Reference: Moreno, N., Tharp, B., Erdmann, D., Rahmati Clayton, S., Denk, J. (2007). The Science of Microbes Teacher’s Guide. Houston, TX: BioEd. Image References: Walsh, J. Cells in Elodea leaf, showing plastids, elodea00. Micrographia , www.micrographia.com. Walsh, J. Onion epidermis. Micrographia , www.micrographia.com. ____________________________________________________________________________ The Science of Microbes and accompanying online professional development were supported, in part, by Science Education Partnership Award number 5R25RR018605 from the National Center for Research Resources of the National Institutes of Health (NIH) to Baylor College of Medicine. The unit was developed in partnership with the Baylor-UT Houston Center for AIDS Research, an NIH-funded program (AI036211). The opinions, findings, and conclusions expressed in this presentation are solely those of the authors and do not necessarily reflect the views of Baylor College of Medicine or the sponsoring agencies.