Cell Model Lab

In order to you a view of how diffusion works with a selectively permeable membrane, here is a lab that uses a plastic bag to model the cell (membrane).

Water with iodine

Cornstarch and water

Iodine and cornstarch Iodine is an indictor. (it shows that something is present) Iodine indicates the presence of starch, it turns blue.

Add a spoonful of cornstarch to the plastic baggie and about 100 ml of water.  Tie the baggie off. The bag is a model of a cell, the cytoplasm is the cornstarch mixture and the plastic is the cell membrane.  Solid objects are not really solid at a molecular level. The bag is more like a tiny little screen door.  If molecules are small enough, they can pass right through the bag.

prepare a beaker of iodine.  Fill it about half full and add several drops of iodine The more concentrated the mixture, the faster the reaction. Iodine is an “INDICATOR” ; it will change color whenever it encounters starch.  You can demonstrate this with a beaker of starch solution and a drop of  iodine.

Place the baggie into the iodine mixture.  Make some predictions about what will happen. Define diffusion and osmosis.  The process will take about 15 minutes.

After 15 minutes

Would there be a color change? What color would result? Iodine and water Cornstarch and water Given what you observed, what do you expect if a baggie of iodine and water were placed in a cup with cornstarch and water? Would there be a color change? What color would result? Where would the color change be?