Diffusion and Osmosis

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Diffusion and osmosis are two types of passive transport. Diffusion is a random movement of molecules from an area of high concentration to an area of low concentration. Osmosis is a type of diffusion that diffuses water through a selectively permeable membrane. There were two parts to the experiment, the dialysis tubing lab and the potato lab.                     In the first experiment, the dialysis tubing acted as a semi-permeable membrane. A semi-permeable membrane is a membrane that allows certain substances to pass through. In this experiment, several variables, including glucose, starch, and iodine potassium iodide were tested for permeability through the dialysis tubing.

In the second experiment, several potato tuber cylinders were tested in different sucrose solutions. The potato cylinders were tested to see what would happen to its mass if they were in different sucrose solutions. There are three major terms that are mandatory to know before experimenting: isotonic, hypertonic, and hypotonic. An isotonic solution is when the solute concentration inside a system is equivalent to the solute concentration outside of a system, thus resulting in no net change of diffusion. In a hypertonic solution, the solute concentration outside of a system is larger than the solute concentration within a system, so water diffuses out of the system to attempt to even out the ratio disparity; this results in the system shrinking in mass. In a hypotonic solution however, the solute concentration is greater within the system than outside of the system, so water diffuses into the system; this results in the system being "bloated".

Activity 3.1 B:
A selectively permeable membrane only allows certain substances to pass through, often small molecules. Since glucose and I2KI are smaller than starch, I hypothesize that they will diffuse through the dialysis tubing, but not starch. Activity 3.3 A:

Osmosis is the diffusion of water that occurs in biological systems to regulate concentration of substances without diffusing the actual chemical. I hypothesize that as the sucrose concentration increase outside of the potato, the potato cylinders will decrease in size and mass. Materials & Method

Activity 3.1 B:
Materials used:
* Dialysis tubing
* String/rubber band
* 30% glucose solution
* Starch solution
* I2KI solution
* Benedict’s reagent
* Beaker
* 3 standard test tubes
* Pipettes

To start the experiment, a dialysis tubing bag was prepared. The end of the dialysis tubing was folded and pleated and tied with a string. Then four pipettes of 30% glucose solution and four pipettes of starch solution were added into the bag. The color of the bag was recorded. Then in a beaker filled with water, several drops of I2KI were added into a beaker until the solution turned visibly yellow-amber. Then the color of the beaker was recorded. The dialysis tubing bag was then placed in the beaker. To make sure that the bag did not spill some of its contents in the beaker it was tied to the beaker with a rubber band. When that was done, the bag was left in the beaker for thirty minutes. After the thirty minutes, the colors were recorded. To test for the presence of glucose, three test tubes were labeled “control”, “beaker”, and “bag”. In the “control” tube, two pipettes of water were added. In the “beaker” tube, two pipettes of beaker solution were added. And finally, in the “bag” tube, two pipettes of bag solutions were added. Then a drop of Benedict’s reagent was added in each tube. The color of each tube was recorded. Then the tubes were placed in boiling water for a couple of minutes. Once the tubes came out, the colors were recorded. Activity 3.3A:

* Seven beakers
* A potato
* A cork borer
* Razor blade
* Sucrose solutions 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 molar (m) * Balance
* Petri dish

First, distilled water and the different sucrose...
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