Osmosis & Selective Permeability

Osmosis is the dispersion of water. Our cells are capable of absorbing nutrients because, the cell membrane is selectively permeable (some molecules can effuse freely through the membrane while others cannot). In this experiment we used dialysis bag as a model of the cell membrane. Our hypothesis was that the glucose will diffuse out of the membrane into the beaker filled with iodine solution. To demonstrate dialysis tubing we used water, starch and iodine.

When starch and iodine react together they form a dark brown color.

Materials Rubber band Dialysis bag Beaker Glucose solution Iodine solution Water, thread Methods Cut a piece of dialysis tubing that has been soaking in water approximately 40 CM (apron. 16 in) long, Tie the end of the dialysis tubing with two or more knots. Fill he bag halfway with glucose solution. And add 4 full droppers of starch solution to the bag. Hold the open end close while you mix the content o the bag.

Rinse of outside the bag with tap water Fill the beaker 2/3 full with distilled water.

Add drops of iodine solution until an amber (tea like) color is apparent. Place bag in the beaker with the open end hanging over the edge. Secure the open end of the bag to the beaker with a rubber band. Don’t let the content spill into beaker. Allow the setup to sit for 30 minutes Record the color of the solution in the beaker and in the dialysis bag after 30 minutes Mark of test tube at 1 CM and 3

Tea Bag Diffusion Experiment

Solute Diffusion across Plasma Membrane Start of the Experiment After the Experiment Content Color Benedicts Test Conclusion Bag Glucose Starch Clear Dark black Starch moved in the bag Water Iodine Amber Yellowish color Urine like color Results the molecules that are small enough can go through easily.

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Molecules like water molecules, but starch molecules cannot go through. That explains the diffusion with the water and the glucose, and the diffusion of the water and not the starch. We started with all the glucose inside the bag with just water and iodine solution on the outside. Conclusion

The glucose molecules are small enough and the solution and the solution was hypersonic (more starch molecules inside than outside the bag). The starch molecules diffuse through the dialysis tubing into the solution in the beaker. This was so that it can reach a dynamic equilibrium so it could even out to an isotonic solution. In our experiment we found out that the starch did not pass though the membrane because, its molecules were too big. We could tell that by noticing the change in color. The solution inside the bag was dark black and the outside was lighter than what we originally start with.