A. NEXT GENERATION SCIENCE STANDARDS HEREIN
DCI’s: LS1.A Structure and Function
Cross Cutting Concepts: Cause and Effect, Systems and System Models, Stability and Change
Scientific and Engineering Practices:
Asking Questions and Defining Problems
Analyzing and Interpreting Data
Developing and Using Models
Constructing Explanations and Designing Solutions
Engaging in Argument from Evidence
Obtaining, Evaluating, and Communicating Information
B. SUGGESTED USES
Prior Knowledge: Students should have a basic understanding of the cell, the cell membrane, and how it works. Basic measuring of volume, and use of electronic or analog balances/scales is assumed.
Implementing the Lesson: I've uploaded this product as a word file, so that you may modify/ eliminate any section or test that you might not have materials for. For example, if you don't have glucose test strips, you might just eliminate the test; it is up to you.
This lab is part of a Unit Bundle on Cell Membranes and Transport. The unit is NGSS aligned. If you are interested, you can find it here:
Get it here: NGSS Aligned: Membranes and Transport Unit Bundle
Looking for a diffusion/osmosis lab that is a little simpler? Check out my lab that uses potato slices (or another vegetable) in order to measure the movement of water into and out of cells in various mixtures. If you are interested, you can find it here:
Get it here: NGSS Aligned: Potato Lab: Diffusion and Osmosis
SAFETY: Although none of the materials in this lab are particularly dangerous, students should wear glove and goggles. Iodine stains clothes (permanently). Remind students to never ingest anything in lab.
Materials and Setup:
12 inches of Dialysis tubing
Starch solution - Stock solution for class (dissolve 10 grams of starch in 1000 ml of warm water)
Glucose indicator strip ($15 at Walgreens)
500 ml beaker
Basic procedure: (will vary because students write protocol)
1. Students are to design the experiment, and write out the procedure, but the basic setup has students tie one end of a dialysis bag, add water, glucose, and starch solution into a dialysis bag, and then tie the other end. The best way to tie it, in my experience is to simply tie a knot (like a balloon) on the ends of the dialysis bag. Be sure to thoroughly clean the outside of bag, and folds of the knots in order to minimize contamination.
2. The students should mass the bag after this.
3. Then students submerge the little "cell" they made into water, add iodine to the water (which will diffuse into the bag, and turn blue inside, showing iodine diffused in, and hopefully starch didn't leak out (too large of a molecule).
4. They will also test the water outside of the bag for glucose, which should show that it moved out of the bag (small enough).
5.Finally, they will mass the bag (after waiting for some time, say 20 mins at least), and see if it gained or loss mass as a proxy for water osmoting into or out of the bag.
2. I often have students design the lab the class before, so I can approve the procedure, and they can have ample time to setup, run, break down, and gather class data.
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