Okay, so I have not been the best blogger, as I am not posting as much as I’d like to. I have had so much going on with my full-time job and other things that some nights I’ve been so tired that I end up going to bed when my kids do. It’s all good though, I’m not complaining, I’m just making an excuse for myself 😊. What matters is that I am finally back with another lesson that I highly recommend. This one's for teaching a lesson on diffusion and osmosis. I know summer is around the corner, so this can be a good lab to include for the next school year, or if you have kids, to try with them this summer. This one is perfect for the cell unit. In this experiment, a plastic bag will demonstrate the role of the cell membrane has in the cell. It is one thing for students to read about diffusion in the notes, but quite another thing for them to see it with their own eyes.
After students have learned about the cell structure and its organelles, you will want to teach them about the different types of transport systems that occur across the cell membrane (diffusion, osmosis, facilitated transport, and active transport). The iodine and cornstarch lab will help students better understand the term, permeable and semipermeable.
If you would like a teaching presentation on the different cell transport systems, I have one in my store that includes student note taking sheets and several review questions at the end of the presentation that check for understanding. My presentation also comes with a worksheet that I made for this lab, but if you ONLY want a worksheet on this lab and not the unit presentation/notes, then you can get one for free here. I liked this one, too.
Why do I like this lab? First, because it builds critical thinking skills. Second, the term diffusion and semipermeable will make more SENSE to your kiddos after they see it in action in this lab. And third, because it’s really EASY to set up. Easy breezy.
OKAY, so once students have completed a lesson on diffusion and osmosis, they are ready to try this lab. What will they need? Just a few things:
1. A 500mL beaker (or another clear container about that size)
2. Sandwich baggies (Use the cheap, thin bags with the fold over top)
3. 1 tablespoon or more cornstarch
4. 50 mL water
5. 10 drops of Iodine solution (this is one I use)
6. Plastic pipette
What's next?
1. Fill your beaker with 500ml water.
2. Next, place the plastic baggie over the top of the beaker and pour half a cup of water to
it. Then add 1-2 tbsp of cornstarch to the water in the baggie. Folding it over the glass should
prevent the starch from entering the beaker, as it needs to be kept in the bag. *See the image
below to see how the baggie is folded over the top of the beaker. You can place the baggie over
the beaker as shown below, then take it out and tie it tightly. The main thing is you DON"T
want cornstarch to enter the beaker-it must remain in the baggie for the entire experiment.
4. Once the cornstarch water is in the bag, remove it and tie or seal it tightly.
5. Using a pipette, add 10 large drops of iodine to the water in the beaker.
6. Place the cornstarch baggie in the iodine water solution and let it remain submerged for 20-
30 minutes.
7. Students will record the changes as they occur in their student handout.
Extensions:
1. Let the baggie sit in the iodine water overnight to show students a GREATER effect.
2.You can also ask students what they think might happen if they were to REVERSE the lab and instead place the iodine water solution in the baggie and the cornstarch and water in the beaker. Let them give you their predictions beforehand, then have them try it out for themselves and see if they were correct or not. Next, have them EXPLAIN the results to you, using what they learned about diffusion.
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