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Biology LibreTexts

1: Osmosis

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  • By Dr. Ingrid Waldron, Department of Biology, University of Pennsylvania, CC-BY-NC 4.0.



    This activity provides a sequence of learning activities designed to optimize student learning and understanding of osmosis by beginning with a student investigation of osmosis at the macroscopic level and then moving to analyzing osmosis at the molecular and cellular levels. In Part I, "What is happening to these eggs?" students observe and analyze the effects of osmosis on eggs. In Part II, "Osmosis – Effects on Animal and Plant Cells", analysis and discussion questions introduce students to a molecular and cellular understanding of osmosis and challenge students to apply their understanding of osmosis to several real-world phenomena.

    • 1.1: Osmosis Protocol
      Most cells are tiny – much too small to see without the help of a microscope. In contrast, an unfertilized chicken egg is a giant cell. In this investigation, you will see that water can cross the cell membrane surrounding an egg. You will investigate which way water moves across the membrane, depending on the type of liquid surrounding the egg. When water moves across the cell membrane, the egg changes in size and appearance.
    • 1.2: Osmosis Teacher's Preparation Notes
      For this activity, Part I will require approximately 15 minutes on three consecutive class days. Part II will probably require the rest of a 50-minute period on the third day. If you can't do Part I as a student investigation, you can present it as a demonstration, which will require less time. A key is available upon request to Ingrid Waldron (

    Thumbnail: The process of osmosis over a semi-permeable membrane. The blue dots represent particles driving the osmotic gradient. (CC BY 4.0; OpenStax via Wikipedia).