I. INTRODUCTION:

Osmosis is the passive transport of water through a semi-permeable membrane. To understand how osmosis works, an investigation was preformed using potato cores. Out of four potato cores that were used, one was dehydrated, one was put in a 0% NaCI solution, one in a 10% NaCI solution and the final one was placed in a 20% NaCI solution. The percentage represents the amount of solute (in this case NaCI) in the solution.

Subject: What is the osmotic affect of varying sodium chloride (NaCI) solutions on the physical characteristics of a potato core?

Hypothesis: If a potato core is placed in the 0% NaCI solution, then the potato core will increase in size because the potato core should be hypertonic to the solution. Also water that was in the test tube should be decreased, for it will have soaked into the core.

If the potato core is put into the 10% NaCI solution, the core should have the reverse affect. The core should decrease in size because the core would be hypotonic to the solution.

This hypothesis goes for the 20% NaCI solution as well. The core placed in the 20% solution should decrease in size as well, for the core should also be hypotonic to the solution.

With both the 10% and 20% NaCI solutions, the water in the test tube should have increased because diffusion would allow the water that was once in the core to move into the solution.

II. METHODS AND MATERIALS:

Day One Procedure: First, get a white potato, then you must get a 5mm diameter cork borer and a small glass rod that is thin enough to remove the core from the borer. Take the borer and with the potato oriented upright vertically, push the borer into the top part of the core and out through the bottom. Then, remove the cork borer with the potato core still in it. Next, take the small thin glass rod and place it in the hole at the top of the core borer's handle. This should allow you enough force to push the core out of the borer. Repeat this process until you have four cores.

Next, using the millimeter side of a rule and a razor blade, cut each core so it's length is 40 mm. At that point, you get a piece of aluminum foil and frame it into a "boat" type shape. Place your aluminum boat on the scale. Measure the weight of your boat to the nearest tenth of a gram using a side arm balance scale. Place the core in the aluminum foil boat. Weigh the boat with the potato in it to the nearest tenth of a gram. Then subtract the weight of the aluminum boat by itself from the weight of the aluminum boat with the potato in it. This will give you the weight of the potato core. Record data in your day one chart. Repeat this step for the other three potato cores. Then, measure the diameter of each potato core in millimeters. After you have found the length, diameter and the weight, you may then calculate the volume of each core using the formula V=(3.14)(r²)(h).

Using a probe, place the potato core designated for the 0% solution into the test tube. Repeat this process for the cores of the 10% and 20% solutions. Then, using a 10 ml graduated cylinder, cover the core with 7 ml of 0% solution. Next, using a different 10 ml graduated cylinder, measure 7 ml of 10% solution and pour it into the test tube labeled 10%. Repeat this step again for the 20% solution. Place the three test tubes on the test tube rack and your aluminum boat with your potato core into the drying oven so it can dehydrate over a period of 24 hours.

Day Two Procedure: Collect your dehydrated potato core, and the three test tubes as well as a scale, three graduated cylinders and probe. Using a side arm balance scale, weigh your dehydrated core. After that, take the 0% solution and empty all the solution out into the first graduated cylinder. This will determine whether the core took in any water or released any water. Using a probe, carefully remove the potato core from the test tube. Place the core on the aluminum foil boat and onto the scale. Weigh the boat and core to the nearest gram. Then subtract the weight of the boat from the total weight of the boat and the core. This gives you the new weight of the core. Then, measure the core in millimeters. Next, measure the diameter of the core. Finally calculate the volume of the core. Repeat these steps for the 10% and 20% cores. Record results on your day two table.

The results from day one and day two will allow you to find the difference between the two days. Calculate the differences and place the information on a chart.

III. Results

IV: DISCUSSION:

V. CONCLUSION: