# Do Some Particles Move By Diffusion? How Can A Model Be Created?

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Problem: Do some particles move by Diffusion? How can a model be created to simulate cell membranes and permeability?

Background: The Plasma membrane is mainly composed up of phospholipids and proteins. The cell membrane determines which molecules can diffuse through the cell. This characteristic of a cell membrane is called selective permeability. Many cells are semi permeable which means that they allow only certain molecules in or out of the the cell. Remember back to the Carbohydrate lab and that starch turns dark midnight blue when tested with Iodine. Also remember that cells are composed up of so many different things suspended in a matrix of so many different things.

In this investigation, you will: Use any materials listed or
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You must have it approved by your teacher before you start collecting data.

Gather all necessary materials:
1 Great Value Baggie, 1 Brand Sandwich Baggie, 8 Graduated Cylinders, 2 Rubber Bands, 2 Beakers, Pen/Pencil

2. Pour 20 ml of water into two graduated cylinders, pour 20 ml of dirt into another pair (2) of graduated cylinders, pour 20 ml of iodine into another pair of graduated cylinders, and pour 20 ml of starch into another pair of graduated cylinders. All 8 graduated cylinders should be filled with 20 ml of a substance.

3. Afterwards, pour 20 ml of starch into two beakers. Both beakers should have 20 ml of starch.

4. Pour 20 ml of iodine into the great value baggie. Once you do, pour 20 ml of dirt and 20 ml of water into it as well. Repeat this with the sandwich baggie. The dirt represents the organelles and the water represents the cytoplasm.

5. Place one baggie into a beaker of starch and the other into the other beaker of starch. The baggies will help to model the cell membrane and cell.

6. Check to see your results and begin collecting data. An important piece of data to collect is whether iodine or anything spills out of either baggies.

Results: In this experiment, both baggies leaked out iodine into the starch. This was demonstrated when the starch surrounding the baggies turned dark purple. The color of the starch changed from white/grey into a darkish purple. When iodine mixes with a