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Cell Model Lab
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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).
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Water with iodine
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Cornstarch and water
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Iodine and cornstarch Iodine is an indictor. (it shows that something is present) Iodine indicates the presence of starch, it turns blue.
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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.
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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.
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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.
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After 15 minutes
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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?
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