BIOL 1208 Lab Report Cover Sheet I certify that the writing in this assignment is my individual work and is my sole intellectual property. It does not contain the ideas or writing of other individuals/authors. _Alexandra DeWitt_______________5/1/13____________ AuthorDate _10_________ Lab Section # Increasing Sucrose Concentrations Causes the Osmotic Concentrations of Disks of Potato Tubers to Decrease Abstract: Introduction: The biological membranes are composed of phospholipid bilayers, each phospholipid with hydrophilic heads and hydrophobic tails, and proteins.
This arrangement of the proteins and lipids produces a selectively permeable membrane.
Many kinds of molecules surround or are contained within cells, but water is perhaps the single most important molecule in any living system (Hayden and McNeil 2012). Since water molecules are so small, they are constantly going into and out of the cell. Osmosis is a situation where more water molecules are moving across the membrane in one direction than the other (Hayden and McNeil 2012). During osmosis the net movement of water molecules will be from a solution that has a lower osmotic concentration to a solution that has a higher osmotic concentration.
When a solution has a higher concentration of solute within the cell than out, it is called hypertonic. When a solution has a lower concentration of solute within the cell than out, it is called hypotonic. And when there are equal concentrations inside and out of the cell, it is called isotonic. The relative osmotic concentration can be determined by a change in mass of the tissue. The purpose of this experiment is to calculate the mass/change in mass of plant tissue, in our case potato tubers. The change in mass of the potato tuber disk determines the osmotic concentration.
After soaking the potato tubers in different concentrations of sucrose, then calculating the percent change in mass, we can determine the osmotic concentration. The null hypothesis is that the molarity of sucrose will not change the osmotic concentration of the potato tuber. It is hypothesized that the higher the molarity of sucrose solution the lower the osmotic concentration. If the hypothesis is true then the change in mass of the potato tuber disks would decrease as the concentration of the sucrose solution is increased.
Materials and Methods: To determine the percent change of mass of the living tissue we used potato tuber cells. The potato tubers were cut into segments of equal width, approximately 4 cm, and placed in a wet towel to prevent the tissue from drying out. Then each segment was sliced into small disks, approximately 2mm. Once the segment was sliced the disks were placed in a beaker and rinsed with tap water. A weigh boat, containing the potato tuber disks, and balance was then used to determine the mass of each of the potato tuber segments.
This was repeated for the other six potato tuber segments. Once the initial mass of each segment was collected, the disks were then incubated each in a different concentration of sucrose; 0. 0 M, 0. 1 M, 0. 2 M, 0. 3 M, 0. 4 M, & 0. 5 M, for one hour. While the disks were incubating each potato-sucrose solution was swirled every ten minutes. Once each segment was incubated for an hour, each solution was removed of the disks and the disks were blotted on a paper towel and then weighed again. The final mass was recorded.
We then used the initial mass and final mass to determine the change in mass of each segment. Results: Measuring the initial mass and final mass of the potato tubers to find the change in mass, then dividing that number by the initial mass and multiplying by 100 determined the percent change in mass. The percent change in mass decreased as the sucrose concentration increased (Figure 1). The percent change in mass decreased as sucrose concentration increased, therefore, relative osmotic concentration also decreased as sucrose concentration increased.
The osmotic concentration was greater than zero in sucrose solutions of 0. 0. The osmotic concentrations were less than zero in sucrose solutions of 0. 1, 0. 4, and 0. 5 M. The osmotic concentrations were zero in sucrose solutions of 0. 2 and 0. 3 M. At sucrose concentration 0. 1 M the change was negative which does not fit the trend line, but if the experiment was repeated a few times that would probably change. The percent changes in mass from 0 to 0. 5 M was very dramatic. Figure 1: Percentage change in potato tuber mass vs. sucrose concentration.
The percent change in mass decreased as the sucrose concentration increased. Relative osmotic concentration was measured as the percent change in mass of sucrose concentration over one hour. Discussion: Cells need waterthis cell was hypertonic, meaning the solution had more solute; these cells were hypotonic, meaning the solutions had less solute; these cells were isotonic, meaning the solution had equal solute. Wischusen, William, Jolissaint, Ann, Reiland, Jane, and Pomarico, Steven. 2012. Biology 1208/1209: Biological Laboratories for Science Majors. Hayden McNeil, Plymouth, Michigan.
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