Lab: Simulating the Cell Membrane Tips + Hints

This lab is a quick and easy way to for students to see diffusion in action. I offer this lab for free on my teachers pay teachers store. You can find it here:

For this experiment you will need:
Cornstarch
Iodine
Beakers
Access to sinks and water
Pipette or eye dropper
Dialysis tubing or plastic baggy
thread

Personally, I like to use dialysis tubing. In my opinion, it is the most tried and true way to get results (I’ve had not so great results with plastic baggies in the past, but they do work most of the time). If you are using dialysis tubing, be sure that students soak the tubing in lukewarm water for a minute while rubbing the tubing between their fingers so that they do not have trouble opening it.
If using dialysis tubing, the students will need to tie off both ends. They should cut about a 5 inch snip of dialysis tubing for easiest handling. If using a plastic baggy, they will need only to tie off one end.
It also helps if the students gently swirl the cornstarch and water before adding the drops of iodine to the beaker. Note that students do NOT directly add the iodine to the cornstarch. Be sure that they understand this. The cornstarch and water is in one container (the plastic) and iodine goes on the outside, in the water that is in the beaker.
Students must understand that the iodine is diffusing into the cornstarch. Cornstarch is too big to diffuse into iodine + water mixture. You can relate this to what they have learned about biochemistry- starches are polysaccharides- long chains of saccharides and are generally quite large molecules. The dialysis tubing represents the cell membrane.

Good luck!

If you are interested, I have included a link amazon below for dialysis tubing. I usually order 2 or 3 of these at one time. 🙂

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