Selectively Permeable Membranes
Students learn that engineers develop different polymers to serve various functions and are introduced to selectively permeable membranes. In a warm-up activity, they construct models of selectively permeable membranes using common household materials, and are reminded about simple diffusion and passive transport. In the main activity, student pairs test and compare the selective permeability of everyday polymer materials engineered for food storage (including plastic grocery bags, zipper sandwich bags, and plastic wrap) with various in-solution molecules (iodine, corn starch, food coloring, marker dye), assess how the polymer’s permeability relates to its function/purpose, and compare that to the permeability of dialysis tubing (which simulates a cell membrane).
Example activity testing stations.Copyright 2016 Jamie Sorrell, RET Program, School of Polymers and High Performance Materials, University of Southern Mississippi
Polymers are used all the time in daily life, and engineers design polymers with a particular structure to support the polymer’s function. For example, a plastic grocery store bag needs to be light and easily packaged as well as sturdy and waterproof to handle your groceries As another example, various forms of zipper plastic bags have been designed for specific purposes, such as for freezer storage (to prevent freezer burn on food) and for refrigerator storage (more permeable). Engineers keep these functional requirements in mind as they design!
After this activity, students should be able to:
- Discuss the process of diffusion and the components needed to make it successful, including a concentration gradient and appropriate molecule size.
- Describe how engineers develop and design different polymers to satisfy desired functions.