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 0.5M 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 0.6M 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...