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Using Sucrose Solutions to Determine Osmolarity of Potato Tubers Based on Weight By Thomas Pelikan Biology 200A Section 004 Kimberly Schmidt October 2, 2012 Abstract: In this experiment we were trying to determine the osmolarity of potato tubers by weighing them before and after incubating them in solutions of sucrose with varying molarities. To find the osmolarity we took a potato and used a cork borer to obtain seven samples of potato tubers. We then prepared seven beakers with concentrations of sucrose ranging from 0.

0M to 0. 6M.

After weighing the potato tubers one by one we cut them in half and placed each halved tuber into each beaker. We incubated them for 1 hour, stirring every 10 minutes. After one hour we removed the pieces and weighed them and compared the initial and final weights to find the percent change in weight for each solution. The results showed that the 0. 0M-0. 3M solutions increased the weight of the potato tubers. The 0. 4M solution of sucrose only increased the weight by 0.

47%. The sucrose solutions of 0. 5M and 0. 6M increased the weight of the potato tubers.

The sucrose solutions of 0. 0M to 0. 3M increased the weight of the potato tubers, supporting our hypothesis. The sucrose solution of 0. 4M only slightly increased the weight of the potato tubers, supporting our hypothesis that the osmolarity of the potato tubers was 0. 4M. The sucrose solutions of 0. 5M and 0. 6M increased the weight of the potato tubers, which did not support our prediction that the weight should decrease, but that was most likely due to errors in removing excess solution from the potato tubers after removing them from the solution.

Introduction: Determining osmolarity in plant cells is important to scientists when performing experiments. In order for normal physiological processes to occur in plant cells, the plant cell must be in an isotonic solution; it must have the same amount of osmotically active substance (OAS) inside the cell as well as outside the cell (Morgan 2011). Knowing the osmolarity of different types of plant cells has many real world applicatons. Such an application would be preserving fruits and vegetables to achieve a “fresh like state” (Shi 2002).

Another would be using osmotic dehydration to dehydrate fruits and vegetables as it is more energy efficient than freeze drying (Tortoe 2008). The objective of this experiment was to use concentrations of sucrose solutions from a molarity of 0. 0 to 0. 6 to determine the osmolarity of potato tuber cylinders based on weight before and after incubation in the solutions. We hypothesized that the solutions of 0. 0M to 0. 3M would have a lower concentration of OAS than the potato tuber and be hypotonic to the potato cells, the solution of 0. 4M would have the same amount of OAS as the potato tuber and be isotonic, and the solutions of 0. M and 0. 6M would have more OAS than the potato tuber and be hypertonic. If the solutions of 0. 0M to 0. 3M had lower OAS than the potato tuber, then the potato tubers would weigh more after incubation in the solutions than before, with the highest weight gain in the 0. 0M solution, and the lowest weight gain in the 0. 3M solution. If the 0. 4M solution had the same amount of OAS as the potato tuber, then the osmolarity of the potato tuber would be 0. 4M and there would be very little or no weight change after incubation in the solution. If the solutions of 0. 5M and 0. M had higher amounts of OAS than the potato tuber, then the potato tubers would have a lower weight after incubation than before, with the lower weight loss being in the solution of 0. 5M and the higher weight loss being in the solution of 0. 6M. Materials and Methods: In this experiment we obtained seven 250mL beakers and filled beaker 1 with 100mL of deionized (DI) water, and filled beakers 2-7 each with 50mL of DI water. We then filled beaker 2 with 50mL of 0. 1M sucrose solution, beaker 3 with 0. 2M sucrose solution, and so on. Then we took a potato, and using a cork borer, obtained seven complete, undamaged cylinders at least 5cm long.

We then lined up the potatoes and cut them to 5cm long, removing the peel, and placed them in a closed petri dish. We then removed one piece and placed it between the folds of a paper towel then weighed it to the nearest . 01 gram and recorded the weight. After recording the weight we immediately cut the tuber lengthwise into halves and placed the potato pieces in the beaker full of water and recorded the time. We then repeated the steps for weighing and cutting the potato tubers for the sucrose solutions of 0. 1M to 0. 6M. We incubated the potato tubers approximately one hour, stirring every ten minutes.

After incubating we removed the potato tuber halves from the 0. 0M solution and blotted off the excess solution, then weighed them to the nearest . 01 gram and recorded the final weight. We repeated the steps for the rest of the tubers, starting with the 0. 1M solution and ending with the 0. 6M solution. After recording the final weights we subtracted the initial weight from the final weight to find the weight change. Then we took the weight change and divided it by the initial weight, then multiplied that number by 100 to find the percent change in weight

In this experiment the independent variable was the concentration of sucrose. The levels of treatment were 0. 0M to 0. 6M concentrations of sucrose solution. The dependant variable was the weight of the potato tubers. The controlled variables were the use of DI water, the amount of time spent in the solution, using tubers from the same potato, using the same length and width of potato tubers, stirring the same amount in every solution, the same volume of liquid in every concentration of sucrose, and weighing each potato tuber to . 01 grams. The control treatment was beaker 1 which contained only DI water.

There was no repetition to this experiment. Results: The purpose of this experiment was to incubate potato tubers in solutions with increasing molarities of sucrose to determine osmolarity based on the weight of the potato tubers before and after incubation. After removing the potato tubers from the beakers, we weighed the pieces and recorded the weights. We then observed the weight change and percent change in weight of the potatoes. In every concentration of sucrose the weight of the potato tubers increased, with the largest change in weight being in the 0. 2M solution of sucrose with a change of 9. %. The smallest change in weight was in the 0. 4M solution of sucrose; the change in weight was 0. 47% (Table 1). The percent change in weight of the potato tubers started high at 0. 0M with a change of 4. 3% and decreased to 2. 4% at 0. 1M, then increased dramatically to 9. 5% at 0. 2M. It decreased again to 0. 48% at 0. 3M then again to 0. 47% at 0. 4M. At 0. 5M it increased to 3. 5%, and then at 0. 6M the weight change decreased again to 1. 0%. The percent change of weight generally decreased from 0. 0M to 0. 4M, and both 0. 5M and 0. 6M are increases from 0. 4M (Figure 1). Table 1.

Using initial weight, final weight, weight change, and percent change in weight of potato tubers after incubation in varying solutions of sucrose molarity to estimate osmolarity of potato tissue Approximate time in solutions: 1 hour Sucrose Molarity| | 0. 0| 0. 1| 0. 2| 0. 3| 0. 4| 0. 5| 0. 6| Final Weight (g)| 2. 20| 2. 14| 2. 07| 2. 11| 2. 14| 2. 05| 2. 03| Initial Weight (g)| 2. 11| 2. 09| 1. 89| 2. 10| 2. 13| 1. 98| 2. 01| Weight Change (g)| 0. 09| 0. 05| 0. 18| 0. 01| 0. 01| 0. 07| 0. 02| % Change in Weight| 4. 3%| 2. 4%| 9. 5%| 0. 48%| 0. 47%| 3. 5%| 1. 0%|

Percent Change in Weight of Potato Tubers vs. Molarity of Sucrose Solution Molarity (M) of Sucrose Solution Figure 1. Percent change in weight of potato tubers after incubation in sucrose solution in Biology 200A-004, October 2, 2012 Discussion: Our hypothesis for this experiment was that the solutions of 0. 0M to 0. 3M would have less OAS than the potato tubers, the solution of 0. 4M would have the same amount of OAS as the potato tubers, and the solutions of 0. 5M and 0. 6 M would have more OAS than the potato tuber. The results of this experiment partially support this hypothesis. We stated that if the solutions of 0. 0M to 0. M sucrose had less OAS than the potato tubers, then the potato tubers would be in a hypotonic solution and gain water through osmosis, increasing the weight highest at 0. 0M and lowest at 0. 3M (Freeman, 2011). This part of our hypothesis and prediction was correct, with the exception of the potato tuber in the solution of 0. 2M sucrose, which had a higher percentage weight gain than both 0. 0M and 0. 1M sucrose. This could be due to the fact that the potato tuber used in the 0. 2M sucrose solution was not a perfect cylinder, the hole cut into the potato while obtaining that sample slightly overlapped a previous hole cut into the potato.

Therefore, that potato tuber had a lower beginning weight, and had a higher surface area so water could enter the potato more rapidly than the other samples, increasing the weight more (Freeman, 2011). Our hypothesis that the solution of 0. 4M sucrose would have the same amount of OAS as the potato tuber was supported by our results. We predicted that if the 0. 4M solution had the same amount of OAS as the potato tuber, there would be very little or no weight change in the potato tuber. In our experiment the potato tuber in the 0. M sucrose solution had the smallest percent change in weight of all the levels of treatment, only a 0. 47% change (Figure 1). The results of our experiment did not support the part of our hypothesis concerning the potato tubers in the solutions of 0. 5M and 0. 6M sucrose. We hypothesized that these solutions would have more OAS than the potato tubers; therefore the weight of the potato tubers would decrease. In our experiment the weight of the potato tubers increased in the solutions of 0. 5M and 0. 6M and had a higher percent increase in weight than the potato tuber in the 0. M solution, which is the opposite of what we predicted. However, toward the end of the experiment we were rushed for time, so the potato tubers in the solutions of 0. 5M and 0. 6M sucrose may not have been dried completely after removing them from the solution after incubation to be weighed. The excess solution on the potato tubers could have contributed to the higher than normal weights. This makes sense because cells placed in solutions that are hypertonic (have more OAS than the cell) should shrivel and decrease in weight, whereas ours did not (Boles, 20111).

Based on our results, we estimated that the osmolarity of the potato tubers was 0. 4M because in the solution of 0. 4M sucrose, the potato tubers had the smallest percent change in weight. This experiment could be improved in a few ways. The samples of potato could be larger so inconsistencies in drying the potato off would not be as significant as in a smaller sample. The amount of time the tubers spend in the solution could be increased so the tubers have more time for osmosis to occur.

There are still some things that are left unanswered by this experiment such as other types of solutions besides sucrose can be used to determine the osmolarity of potatoes, if different results would be obtained if a larger sample of potato was used or a larger volume of solution. The last question to be answered is the exact osmolarity of potato tubers, which can be obtained by repeating the experiment a few more times and with the improvements suggested References Cited Tortoe C, Orchard J, Beezer A. “Artificial Cell Studies in Simulated Apple and Potato Starch Cell Complex During Osmotic Dehydration. Journal Of Food Quality [serial online]. October 2008;31(5)559-570. Shi J, Le Maguer M. “Osmotic Dehydration of Foods: Mass Transfer and Modeling Aspects. ” Food Reviews International [serial online]. November 2002;18(4):305. Morgan, J. G. and Carter, M. E. B. Symbiosis: Benjamin Cummings Custom Laboratory Program for Biological Sciences (Cell and Molecular Biology, Genetics &Evolution)- Southern Illinois University Carbondale, pp. 83-99, 2011. Freeman, S. Biological Science- Fourth Edition. San Francisco: Pearson Benjamin Cummings, 2011.

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