Cell wall transport

Essay by agakutynaA-, March 2005

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Part 1 - Diffusion through an Artificial Membrane


This experiment will demonstrate differential permeability in the model cell.


Because iodine is much smaller than starch, Iodine solution will move through the membrane but starch will not.


Prepare iodine solution in jar. Pore glucose solution and starch solution into membrane bag. Gently set the bag in the iodine solution. Observe and check for color changes. Iodine molecules in the solution (orange) will flow by diffusion through the pores in the bag to the inside, where there is no iodine yet (flow is from concentrated to dilute). When iodine bumps into cornstarch molecules, they react to make the dark blue complex.


Iodine solution Glucose/starch solution

before yellow white

after yellow green blue


In dialysis, small molecules pass through a membrane by diffusion. It is like dust blowing through a screen window while keeping bugs out. Diffusion also predicts which direction the molecules will move, which is from more concentrated to more dilute areas.

Here a plastic bag was the membrane. Iodine, starch, glucose and water were the molecules. Starch and iodine combine to make a dark blue product and this was the visual test of your model. Iodine solution was able to move through the membrane but starch was not because iodine is much smaller than starch

Part 2 - Diffusion at Different Temperatures


This experiment will demonstrate the effect of temperature on the rate of diffusion.


Higher temperature will make diffusion faster.


Transfer a few grains of potassium permanganate into three test tubes and fill with distilled water. Place one test tube in each cup. The 3 measuring cups are filled each with the same amount of water, ice and very hat tap water. Measure the level of any color rise up -...