Estimating Osmolarity by Change in Weight
By: Sondus Kahil
27 February 2012
TA- Ashley Hintz
Biology 200A-section 002
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...
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. .
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