Word Count: 1491 |

Section 18
By: Julio C. Quiroga
February 6, 2008
The main point of this experiment was to estimate the osmolarity in a potato tuber cell. Osmosis is when water crosses any semi-permeable barrier such as the cell wall or membrane from a low solute concentration to an area of high solute concentration. The test was to determine the molarity of solution at which potato does not absorb water. Seven tuber cylinders of potato were incubated in a series of sucrose solutions to determine at what molarity the water will not have change in weight. If the solution is more concentrated with solute then the mass should go down. This can happen because the concentration is made even inside and outside of the potato so water has to be removed to equal the concentration levels. The opposite will happen in weaker solutions, as water has to be placed in so the potato will swell up and weigh more. Because every day, sciences, botanist and simple farmers need to find out the optimum water content for normal physiological process in plants this is a very important experiment. Therefore, they are aware that for normal activities to take place, the amount of water w88888888888= levels. Without this process, plants will not produce at their potential capacity and then decreasing their essential functions.
The objective of this experiment was to identify the ability of particle to cross the cell wall by diffusion, and notice the effect of isotonic, hypotonic and hypertonic solution on cells. Diffusion is a physical process in which particle or molecules travel from a region of high concentration to an area of low concentration. The diffusion of water into and out is called osmosis. When these two solutions are separated by the membrane with different pressures it is known as osmolarity. If two solutions separated by a selective permeable membrane have the same osmolarity, they are said to be isotonic solution. When two solutions differ in osmolarity the one with the greater concentration of solute is said to be hypertonic and the more dilute solution is said to be hypotonic solution. Osmolarity play a very important role in any biology and microbiology branch. For example an article by the University of Illinois College of Medicine states that by having a high osmolarity it can be a signal for dectecting algD transcription in mucoid and nonmucoid pseudomonas aeruginoda strains. This is a Chronic lung infection with mucoid, alginate-producing strains of Pseudomonas aeruginosa is a major cause of mortality in cystic fibrosis (CF) patients (A Berry, J D DeVault and A M Chakrabarty, 1989).
For this experiment tree hypothesis will be predicted. First hypothesis occurs when the potato tubes are in a higher concentration of the solution than the concentration of water, i.e. the solution is concentrated, and then the potato tubes will lose mass and become smaller. This is because the concentration of water outside the potato cylinders is concentrated, and there is not much water. Due to osmosis the water inside the potato cylinders will move out. This will decrease the mass of the potato, make it smaller and make it flaccid due to the loss of water. The potato cells lose turgid and become flaccid. The second theory takes place when the potato tubes are in a lower concentration of the salt solution than the concentration of water, i.e. the solution is dilute, then the potato tubes will gain mass and become larger. This is because the concentration of water outside the potato cylinders is dilute, and there is a lot of water. Due to osmosis the water outside the potato cylinders will be taken in. This will increase the mass of the potato, make it larger and make it turgid due to the gain of water. The potato cells gain turgor and become turgid. The last suggestion is that there will be a point at which the potato neither take in nor lose water leading to no change in mass and size. This will happen because when the potato tubes are in an isotonic solution. This is where the concentration of the solution in the cell sap is the same as the concentration of the solution outside it. This would mean that osmosis would not occur. If osmosis does not occur due to the equal concentration inside and outside the cell then there will not be any change in size and mass.
For this experiment 100 mL of DI water and 100 mL of each of the sucrose solutions was obtained and put in 7 different 250 mL beakers. Once the DI water and the sucrose solution were ready, seven cylinders of potatoes were obtained by pushing the borer through the length of the potato and then pulling it out. After removing the borer from the potato, the seven cylinders were pushed out of the borer and lined up to be cut at least 5 cm long by using a sharp razor. The seven potato samples were placed in a petri dish and were kept covered to prevent them from drying out. After a short time, the seven potato samples were removed from the petri dish and were blotted between the folds of a paper towel. The potato cylinders were weighed in a plastic weighing dish on the balance, and the weight of each sample was recorded in a table. After that, the cylinders were cut lengthwise and transferred to the water beaker. Each sample of potato was incubated with a solution from 0.1M to 0.6M and time was recorded immediately. While the potato samples were incubating, every 10 to 15 minutes each beaker was swirled. After the 2 hours, each piece of potato was removed and weighed and the time was recorded when the sample was removed. Finally, each sample was removed from the water, dried out and the final weight was recorded.


Data for Experiment Estimating Osmolarity by Change in Weight
0.0 0.1 0.2 0.3 0.4 0.5 0.6
Final weight (g) 3.06 2.70 2.77 2.65 2.50 2.22 2.33
Initial weight(g) 2.76 2.63 2.75 2.65 2.73 2.68 2.88
Weight changes(g) 0.3 0.07 0.02 0 -0.23 -0.46 -0.55
% change in weight (g) 10.8 2.66 0.72 0 -8.44 -17.16 -19.09

This result indicates that at 0.3 M sucrose solution, the process of osmosis stopped, and isotonic was present. Even though the sucrose solution was 0.0 M, we can see that diffusion was occurring in a minimum way. However, at 0.1M the difference in diffusion was very high compare to 0.0M. When the solution was at 0.2 M diffusion was occurring but in a slow way compare from 0.0 to 0.1. When the solution was 0.3 no diffusion occurred during this time, at this point isotonic solution was present. However, at 0.4M diffusion started occurring again, but this time by losing concentration. The loss of concentration was twice as much at 0.5 M as at 0.4M. Thus, hypertonic solution occurred from 0.0M to. 02M and isotonic solution occurred at 0.3M. Also hypotonic solution occurred from 0.4M to 0.6M.
By increasing the sucrose molarity the weight in grams of the potato changed, just as it was predicted at the beginning. Because of this experiment the stages of osmolarity were demonstrated it. For example, the three stages (hypertonic, isotonic, and hypotonic) can be observed. Therefore, the method that was used was very good, as the data was mostly accurate. The best things about these investigation were that the results were pretty accurate but it could have got some better results (more accurate) by getting each cylinder exactly the same mass to begin with, as this would show a better pattern. Although they weren’t 100% accurate the results were still very good. The main things that may have caused odd results are if the cylinders aren’t measured properly the percentage change could be very different.
Everything went as planned which meant the experiment was a success. If it was to do the experiment again then we would make absolutely sure that each cylinder was the same in all dimensions and mass to keep the results as accurate as possible as this may give us slightly more improved results. We could improve the plan and experiment by maybe increasing the range of Molar concentrations of which we placed the potato cylinders into so there can be a more definite pattern on the graph. We could further add to the evidence by doing the experiment for longer and wait until the mass stops changing and this would give much more reliable and better results. By knowing and recognizing these stages a scientist or farmer can decide the amount of solute to apply to the plant, and therefore, have more control over its production.

Berry A, De Vault JD and Chakrabarty. “High osmolarity is a signal for enhanced algD transcription in mucoid and nonmucoid Pseudomonas aeruginosa strains” J Bacteriol 171 (1989) : 2312-2317
Campbell, Neil, and Reece, Jane. BIOLOGY Seven Edition. New York: Benjamin, 2004.

Morgan ,Judith and Brown Carte, Eloise. INTRODUCTORY BIOLOGY CELL BIOLOGY AND GENETICS Boston: Pearson Custom publishing, 2007.

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