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Activity (Hands-On)Grades 6 - 8

Just Like Kidneys: Semipermeable Membrane Prototypes

Using ordinary household materials, student “biomedical engineering” teams design prototype models that demonstrate semipermeability under the hypothetical scenario that they are creating a teaching tool for medical students. Working within material constraints, each model consists of two layers of a medium separated by material acting as the membrane. The competing groups must each demonstrate how water (or another substance) passes through the first layer of the medium, through the membrane, and into the second layer of the medium. After a few test/evaluate/redesign cycles, teams present their best prototypes to the rest of the class. Then student teams collaborate as a class to create one optimal design that reflects what they learned from the group design successes and failures. A pre/post-quiz, worksheet and rubric are provided.

A side-view drawing shows diffusion over a semipermeable membrane. From left to right: Most particles (red dots) are on one side of a container of liquid that is divided vertically by a membrane. An arrow labeled “time” points to the right where in the same container, the particles are now spread out equally on both sides of the membrane.Over time, certain molecules pass through semipermeable membranes while others are unable to.

Creating models and prototypes is an essential and iterative step in the engineering design process. Engineers build, use and revise models to explore and demonstrate how things work. This is especially helpful for processes that are too large or too small to see. Models and prototypes also enable cost saving because they are a good way to uncover any potential problems before spending for full-size construction or fabrication. Kidney dialysis is a good example of engineering technology in the medical field.

A photograph shows a man leaning back into a chair with his left arm resting on its armrest. Tubes inserted into his arm are connected to a nearby machine with a monitor and dials.A man receiving dialysis treatment.

After this activity, students should be able to:

  • Define diffusion, osmosis and semipermeable.
  • Explain the importance of a semipermeable membrane.
  • Follow the steps of the engineering design process as they create prototypes.
  • Discuss and compare design successes and failures to come up with an optimal design.

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