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Osmosis and Diffusion AMC

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  • Pages: 10
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  • Category: Chemistry

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Diffusion involves the movement of solute particles across a selectively permeable membrane from higher to lower concentrations. A selectively permeable membrane allows only some thing to go through. Water and oxygen are examples of molecules that are able to go through the membrane by diffusion. The net movement of these particles happens down the concentration membrane. Both diffusion and osmosis are passive processes meaning no energy in ATP is needed. When molecules are even throughout the space its called equilibrium. Osmosis is the diffusion of water across the selectively permeable membrane. Water will move in the direction where there is a higher concentration of solute ( meaning, a lower concentration of water) . In osmosis different concentrations of solutes are compared. A solution that has equal concentrations of solute is isotonic. A solution with a higher concentration of solutes is hypertonic and one with less concentration of solutes is hypotonic. “The term osmolarity is used to describe the number of solute particles in a volume of Gluid. Osmoles are used to describe the concentration in terms of number of particles.”

It is deGined as the number of osmoles of solute per liter of solution. Introduction: Experiment A: Research Question: How does the amount of solute in a solution affect a potato tuber tissues weight? o Hypothesis: If the solute concentration in the solution is high , then the potato tuber tissue will lose weight because they will lose water through osmosis. o Independent Variable: Salt in the solutions  Dependent Variable: Weight of the potato tuber o Control: Beaker with distilled water, size of the potatoes Experiment B: o Research Question: How to bigger molecules react to a selectively permeable membrane? o Hypothesis: If starch diffuses through the semi-­‐permeable membrane, to an area of lower concentration, then the substance will change color as an indicator. From a yellowish substance to a more transparent one.

 Independent Variable: Starch added to the substance o Dependent Variable: Color of the substance o Control: controlled test tubes with water, Benedict reagent and iodine solutions Materials: Experiment A: o o o o o o o o o o 60mL of distilled water Beaker 15% salt solute 7 cups or beakers to put the solutions Razor blade Potatoes Petri dish Balance Timer Graduated cylinder Experiment B: o o o o o o o o o o o o 15 cm piece of dialysis tubing String Pipette 30% glucose Starch solution 300mL of water 400 to 500mL beaker Dropper Iodine solution 3 test tubes Benedict reagent Hot plate to boil water Procedure: Experiment A: 1. Measure out 60mL of distilled water into a beaker, and 60mL of each of the following SUCROSE solutions into separate beakers/cups: 0.1 M, 0.2 M, 0.3M, 0.4M, 0.5M and 0.6M. At your table, label each beaker/cup clearly with tape indicating which solution. 2. Use a sharp cork borer to obtain 7 cylinders of potato. Push the borer through the length of the potato, twisting it back and forth (CAUTION: use EXTREME CARE, hold the potato in such a way that the borer will NOT PUSH THROUGH into your hand!)

3. Line up the potato cylinders and using a sharp razor blade and ruler, cut all cylinders to a uniform length about 5 cm, removing the peel from the ends. 4. Place all 7 cylinders in a petri dish, and keep them covered to prevent air from drying them out. 5. Remove a cylinder from the petri dish and place it between the folds of a paper towel to blot sides and end. 6. Weigh it to the nearest 0.01 g on the balance. Note: remember to calibrate the scale before you use it. (Press the ON-­‐Zero). Record the weight in the data sheet below. 7. Immediately cut the cylinders lengthwise into two long halves. This increase surface area. Why do you think this helps the experiment? 8. Transfer the halves into the water beaker and make sure they are SUBMERGED. Note what time the pieces are placed in the water beaker. 9. Repeat steps 5-­‐8 with each potato cylinder. Placing the potato pieces in the appropriate incubating solution. 10. Incubate for 30 minutes (move to the next experiment while you wait) 11. Swirl each beaker every 10 minutes as they incubate. 12. At the end of the incubation period, record the time when the potato pieces are removed.

13. Remove the potato pieces from the Girst sample. Blot the pieces in a paper towel, removing excess solution. 14. Weigh the potato pieces from the Girst sample and record the Ginal weight. 15. Repeat this process until all samples have been weighed in chronological order that they were placed. 16. Record data in the table below. 17. Processed data: Calculate and record the percentage change in weight for each concentration sample, using the formula: 18. Percentage change in weight= (weight change/initial weight) x 100 Experiment B: 1.Prepare the Dialysis bag with initial solutions: a. Fold over 3 cm at the end of a 15 cm piece of dialysis tubing that has been soaking in water for a few minutes, pleat the folded end “accordion style” and close the end of the tube with the string or a rubber band, forming a bag. This procedure must secure the end of the bag so that no solution can seep through. b. Roll the opposite end of the bag between your Gingers until it opens and add 4 pipettesful of 30% glucose into the bag. Then add 4 pipettesful of starch solution to the glucose in the bag. c. Hold the bag closed and mix its contents. Record its color.

Carefully rinse the outside of the bag in tap water. d. Add 300mL of water into a 400 to 500mL beaker. Add several dropperful of Iodine solution to the water until it is visibly yellow-­‐amber. Record the color. e. Place the bag in the beaker so that the untied end of the bag hangs over the edge of the beaker. Do not allow the liquid to spill out of the bag. If the bag is too full, remove some other liquid and rinse the outside of the bag again. If needed, place a rubber band around the beaker holding the bag securely in place. If some of the liquid spills into the beaker, dispose of the beaker water, rinse, and Gill again. f. Leave the bag in the beaker for about 30 minutes. g. After 30 minutes, remove the bag and stand it in a dry beaker. h. Record the Ginal color of the solution in the bag and the Ginal color solution in the beaker. i. Perform the Benedict test for the presence of sugar in the solutions. i. Label three clean test tubes: control, bag, and beaker. ii. Put 2 pipettesful of water in the control tube. iii.

Put 2 pipettesful of the bag solution in the bag tube. iv. Put 2 pipettesful of the beaker solution in the beaker tube. v. Add 1 dropperful of Benedict reagent to each tube. vi. Heat the test tubes in a boiling water bath for about 3 minutes. vii. Record the results. Data Collection and Processing Experiment A: Raw data: for the Change in mass in the potato tubers after being in their independent solutions for more than 30 minutes (+/-­‐ 0.1g) Formula for % Change in Mass: Percent change in weight = (Weight change/Initial weight) x 100 ALL measurements in the table above where measured in grams. Osmolarity: 0.239178 osmol/L -­‐ As the solute levels of the solutions increase, there was a bigger weight change in the potatoes. This is because the more hypertonic a solution is the more water the potato tuber will loose, hence the weight change will be more evident. The trend line shows the prevailing direction of the data as a visual representation, and the point where it intersects the x-­‐axis is the Osmolarity. Experiment B: Observations: The initial solution of 300mL of water with Iodine solution was initially a clear yellow color and the glucose and starch solution white. After the bag settled in the substance for more than 30 minutes the solution with iodine was lost its yellowish pigment and became closely transparent. The initially white substance inside the bag, separated into different colors but it was mainly transparent.

Test tube observations: At Girst the three test tubes had the same light blue color. The control test tube remains the same light blue color after boiling. The bag test tube at Girst starts to get yellowish orange, and later on a darker orange. The beaker solution test tube at Girst gets a yellowish green color that then turns into the darkest reddish orange color. Conclusion: Experiment A: Based on the results obtained, the higher the sucrose concentration the lower was the Ginal weight of the potatoes. The lowest percent change in mass of one the potatoes were the control (0.0 M), and the one in the 0.1M solution. They presented a weight change of 14.7% and 10.1% respectively, in contrast to the 28.7% and 17.4% weight change in the potatoes in the 0.5 and 0.6M solutions. The hypothesis was supported by the data obtained because it stated that the potatoes’ tubers’ tissue would loose more weight the higher the solute factor in the outside solution. When the potato tubers’ where placed in high-­‐in-­‐solute solutions it dehydrated the the potatoes tissue making it loose weight.

The water inside the potato was forced to leave the inside of the tissues cells because of the higher solute concentration outside the cell by the process of osmosis. In contrast the potato tuber placed in distilled water (0.0M) had a different kind of weight change. It’s % weight change was 14.7%. The potato tuber tissue cells naturally recognized that there was a higher concentration gradient of solute inside the cell that on the distilled water. This forced the cells to admit more water coming in, hence it made the potato tuber gain mass. The data collection resulted in a osmolarity of 0.239178 osmol/L. The trend resulted this way because the water in the potato tubers tissue cells moved inside and outside causing weight changes in the potato pieces. This experiment concluded that when the potato tubers gained weight it was because they where placed on a hypotonic solution that made them gain water-­‐weight through osmosis. And when the potato tubers lost weight it was because they where placed in hypertonic solutions that made the tissue cells dehydrate or shrink by loosing water that resulted in the potato piece loosing weight.

Experiment B: The results showed the diffusion of starch across the semi-­‐permeable membrane to an are of high concentration to an area a low concentration. This process was proved by the color change of the substances as an indicator and by the Benedict reagent Ginal test tube testing. The hypothesis was again proved because the starch diffused through the membrane leaving the initially white of glucose and starch substance inside the dialysis bag clear and the initially yellowish substance in the beaker containing the dialysis bag a much more transparent color. The test tube observations demonstrate that the beaker solution had the higher presence of sugar. The substance inside the dialysis bag also had sugar but less that the beaker solution. The controlled test tube did not change its initially light blue color as an indicator of no presence of sugar. This results where obtained because of the diffusion of starch from an area of high concentration to an area of lower concentration.

Both: Based on the results from both experiments, osmosis and diffusion are demonstrated to be processes that occur at every moment as an essential process of cells. Both of the experiments showed the diffusion of water or solutions across the concentration gradient. In the case of the potato tuber tissue it occurred as the diffusion of water from an area of high water concentration to an area of low water concentration. In the case of the starch in experiment b, the diffusion of starch through the permeable membrane happened from an area of high concentration to low concentration of starch. The errors possible in the experiments are mostly human errors. In experiment A not all of the potato tubers were cut into the exactly same size. Also some of the potato pieces could have been damaged when the solutions with them were stirred, there also could have been a difference in the way each of them where stirred after the ten minutes.

Not all of the potatoes where dried the same with the paper towel before weighing them. Another factor affecting the result may be that not all the potato pieces where placed or removed at the same time as the others. To improve the lab the experiment it can be made in a closed system to prevent the air from drying the potatoes out more efGiciently. The potatoes can be all cut to exactly the same size using a tool to cut them at the same time, and to improve the accuracy of the weight of the potatoes the weights can be used as the original numbers, or grater amount of signiGicant Gigures used instead of rounding. For experiment B more accurate measures of each substance could have been used, hence more accurate measuring tools also.The amount of time for the bag to rest in the beaker can be increased for better and clearer results in the diffusion and color changes.


Bowen, R. “Osmosis.” Osmosis. N.p., 30 Jan. 2010. Web. Oct. 2014. . Helmenstine, Anne Marle. “What Are Osmolarity and Osmolality?” About. N.p., n.d. Web. Oct. 2014. tm>.

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