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My group and I conducted the experiment that estimates osmolarity by change in weight of potato tubers, this was conducted in order to explore the process of diffusion and osmosis and more importantly to investigate the question of “Does different concentrations of sucrose solutions have an effect on the final weight for the potato tubers?” In this experiment we estimated the osmolarity of potato tuber cores by submersing different potato cores into sucrose solutions of 0.0-0.6M, and weighing the potato.
The results showed the weight of the potato tubers had the highest percent change in weight meaning that they weighed more than the initial weight in sucrose solutions from 0.0-0.3M; it also showed that sucrose concentrations from 0.4-0.6M the weight of the potato tubers decreased. My group and I concluded that the osmolarity of the potato was about 0.4M since the weight of the potato decreased by about -1.3%, which was the closest value to the initial weight of the potato tuber.
We also found that the potato was hypertonic to sucrose solutions of 0.0-0.3M and hypotonic to 0.5-0.6M.
Introduction:
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. According to the book Biological Sciences, “Osmosis is a type of diffusion that occurs when solutions are separated by a membrane that is permeably to some molecules but not to others, that is, a selectively permeable membrane” (Scott 2011). To further explore the process of diffusion and osmosis, we conducted an experiment that would demonstrate these processes and also investigate the question of “do different concentrations of sucrose solutions have an effect on the final weight for the potato tubers?” In my group’s experiment our goal was to estimate the osmolarity of potato tubers from weight change. The hypothesis for this experiment was, “if the concentration of the sucrose solutions in which the potato cylinders are in is changed, then I hypothesize that the final weight of the potato will also change.”
And the prediction that my group and I formed was “if the weight if the potato tuber changes when submerged in different sucrose concentrations, then I predict the weight change will decrease as the sucrose concentration increases.” In my group’s experiment, several potato tubers were tested in different sucrose solutions ranging from 0.0-0.6 M. The potato tubers were then submerged into all the solutions to test osmolarity and to see what would happen to its mass if they were in different sucrose solutions. To fully understand the purpose and understand the results obtained there were three major concepts important to know, they are hypertonic, hypotonic, and isotonic.
According to the journal The American Biology Teacher, “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” (Marvel, Kepler 2009). 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”.
Materials and Methods:
The materials that my group and I used in our experiment was 1 large potato, a cork borer this is necessary to obtain seven potato tuber cylinders. Forceps were needed and a balance that weighs to the nearest 0.01g, a Petri dish, razor blade, paper towels, ruler, calculator, and also necessary for the experiment to work was sucrose solutions from 0.1-0.6 molar. Deionized water was used to represent 0.0 molar in our experiment and seven 250ml plastic cups.
First, my group and I obtained 50ml of deionized water and 100ml of each of the sucrose solutions and put each solution in separate and labeled 250ml paper cups. Then by using a cork borer we obtained seven cylinders form the potato by pushing the borer through the length of the potato and removing the potato from the borer. Making sure none of the cylinders were damaged, we modified the length of each cylinder to 5ml and repeated this step seven times until we had a total of seven undamaged cylinders of equal length with the peels removed from each length using a razor blade. We then placed all seven cylinders into a Petri dish and kept them covered to prevent from drying out. Before weighing each of the cylinders we placed each one between folds of a napkin to blot out the sides and ends and then weighed them individually to the nearest hundredths of a gram on the balance. After doing this step we recorded the results in our table.
After weighing the potato cylinders we immediately placed each in different molar solutions starting with 0.0M through 0.6M. After the cylinders were submersed in the cups we recorded the time witch was 3:20 pm. We then took the cylinders out of their solutions at 4:30pm and calculated the incubation time to be 1hour 10 minutes. The instructions said to leave for 1.5 hours to 2 hours but due to time constraints we took them out a little earlier. After removing the cylinders from each sample we blotted each with a paper towel to remove excess solution only.
After doing this my group and I recorded the final weights of each of the cylinders in the chronological order in which they were initially placed, and recorded it in our table. After recording our data we finally calculated the percent weight change for each of the cylinders. Our group then decided what the variables were and agreed that the independent variable was the concentration of the sucrose solution and the dependent variable was the percent change in weight. This experiment was repeated only once in the given time we had.
Results:
The osmotic concentration was determined by measuring the percent change in mass of the potato cylinders. Change in mass was measured of seven solutions, each containing different levels of concentration 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6M. The percent change in mass decreased as sucrose concentration increased, therefore, relative osmotic concentration also decreased as sucrose concentration increased. However, the osmotic concentration of 0.3 M sucrose solution was relatively greater than that of 0.2 M sucrose solution.
In sucrose concentration 0.6 M, the osmotic concentration decreased almost double from that of 0.5, and significantly from those of all other sucrose concentrations. The osmotic concentrations were greater than zero in sucrose solutions of 0, 0.1, 0.2, and 0.3 M; these cells were hypotonic, meaning the potato had more solute. The osmotic concentrations were less than zero in sucrose solutions of 0.4, 0.5, and 0.6 M; these cells were hypertonic, meaning the solutions had less solute. Osmotic concentration decreased as sucrose concentration increased and cells became more concentrated. Table 1: Data for Experiment Estimating Osmolarity by Change in Weight Sucrose Molarity (M)|0.0|0.1|0.2|0.3|0.4|0.5|0.6|
Final weight (g)|2.57|2.43|2.48|2.24|2.21|2.05|1.82|
Initial weight (g)|2.23|2.18|2.28|2.03|2.24|2.19|2.06|
Weight change (g)|0.34|0.25|0.20|0.21|-0.3|-1.4|-0.24|
% change in weight|15.2%|11.5%|8.8%|10.3%|-1.3%|-6.3%|-11.7%|
Discussion:
When starting this experiment my group and I formulated and agreed upon the hypothesis of ““if the concentration of the sucrose solutions in which the potato cylinders are in is changed, then I hypothesize that the final weight of the potato will also change.” My group and I also agreed upon the prediction of “if the weight of the potato tuber changes when submerged in different sucrose concentrations, then I predict the weight change will decrease as the sucrose concentration increases.” After conducting the experiment and obtained our results, we found that our results support our hypothesis and prediction. The experiment supported our prediction because the sucrose solution diffused from areas of high concentration to areas of low concentration, thus affecting the final weight of potato cylinders when submerged in varying amounts of sucrose concentrations. According to the article Diffusion, Osmosis and Cell Membranes,”There are two ways that the molecules in a solution move: passive transport and active transport. Active transport requires that the cell use energy that it has obtained from food to move the molecules (or larger particles) through the cell membrane. Passive transport does not require such energy expenditure, and occurs spontaneously (Mccandless 1998).
Because the molecules in the sucrose solutions in our experiment were moving with the gradient meaning they were moving form areas of high concentration to areas of low concentration we found that the movement of the molecules was passive transport. The principle means of passive transport is diffusion. Diffusion is the movement of molecules from a region in which they are highly concentrated to a region in which they are less concentrated. In the solutions ranging from 0.0-0.3M the potato acted as the ‘system’ and the solution concentration inside the system was greater than outside which was the sucrose solution, so water diffused into the system (potato) and caused it to become bloated. In the sucrose solutions 0.4-0.6 it was hypertonic because the solution concentration was larger than the system’s concentration so the cylinder decreased in size. This experiment allowed us to take a closer look at the biological process of life and how and why it works the way it does.
This experiment allowed us to a take a deeper look into the mechanisms of diffusion and osmosis and apply it real life examples. According to the book, Cell and molecular biology: concepts and experiments,” When a diluted solution and a concentrated solution are separated by a membrane, there is a net transfer of the solvent from the diluted solution to the concentrated one. Entry of water into root hairs and movement of water within the plant body are good examples of osmosis” (Karp 1991). Osmosis plays a significant role in life first, “the entry of water in to the roots from the soil takes place by this process, cell to cell diffusion of water is controlled through this process, young cells require turgid condition for their growth which is fulfilled by osmosis, and last turgidity of cells is maintained by the process of osmosis” (Karp 1999).
A few errors were made in the experiment but none were significant enough to heavily affect our results. For example, the lengths of the individual potato cylinders may have differed slightly; we may have made mistakes when measuring a specific amount of the sucrose concentrations. We also believe that the potato cylinders should have been incubated longer, ours incubated for 1 hour 10minutes and the instructions said to incubate for at least 1.5 hours.
For the most part these mistakes seemed to be small and not significant because in the end our prediction and hypothesis was supported. I thought that this was an interesting lab to participate in especially because this experiment has been conducted several times by other biology labs, I don’t really believe there were any significant weaknesses to our experiment except maybe the time. It would have been better to have more time to further explore our results. This experiment was conducted smoothly and without complications, and even better supported our prediction. Some questions that would be interesting to be answered by further research is would temperature affect the rate of diffusion in sucrose concentrations?
Works Cited
Freeman, Scott. “Lipids, Membranes, and the First Cells.” Biological Sciences. 4th ed. Vol. 1. Boston: McGraw Hill, 2011. 90-91. Print. Karp, Gerald. Cell and Molecular Biology: Concepts and Experiments. New York: J. Wiley, 1999. Print Marvel, Stephen C., and Megan V. Kepler. “A Simple Membrane Osmometer System & Experiments That Quantitatively Measure Osmotic Pressure.” The American Biology Teacher 6.7 (2009): 355-62. Print. Mccandless, John. “BIOLOGY.ARIZONA.EDU.” BIOLOGY.ARIZONA.EDU. University of Arizona, 27 Feb. 1997. Web. 26 Feb. 2012. .
