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Biology report:water potential

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Introduction

Comparing the water potential of two plant tissues Biology report No. 3 Name : Nebojsa Radisic Mentor: Bernarda Devetak School: Druga Gimnazija Maribor Date: 9. 11. 2007. Introduction Osmosis is defined as a spontaneous movement of water molecules across a semipermiable membrane. Membranes of cells are usually impermiable to large - molecule organic compounds such as polysaccharides, though permiable to water and other, smaller organic compounds. During the process of osmosis, the H2O molecules move down the solute concentration gradient. This means that the water moves from an area of lower solute concentration to an area of a higher solute concentration, thereby increasing the osmotic pressure in the second area, and decreasing it in the first. The vaster the amount of H2O molecules the bigger their potential energy is, also known as water potential. Furthermore, a hypertonic environment of a cell (i.e. the concentration of solutes outside of the cell surpasses the concentration inside it) will extract the water from the cell, whereas a hypotonic solution will "inject" water molecules inside the cell, increasing its size and pressure inside it. ...read more.

Middle

of sucrose in solution (mol/dm?�) 0 0,2 0,4 0,6 0,8 1 Masses of specimens before and after submerging the samples into the solution (in grams) Sample No. 1 4,32 5,87 4,6 5,06 4,21 4 4,47 3,87 4,6 3,06 4,31 3,28 Sample No. 2 4,38 5,28 4,52 4,85 4,76 4,59 4,39 4,01 4,31 3,39 4,29 3,13 Sample No.3 4,75 5,68 4,66 4,97 4,36 4,23 4,48 3,92 4,6 3,53 4,25 3,09 Table 3 - Change in potato samples' masses after being submerged into sucrose solutions of different concentrations By processing the aquired data above, we came up with average percentage changes in masses of samples and presented them in Graph 1. Graph 1 - Percentage of changed mass in samples Experiment 2 Materials and methods Samples of apple and potato, sized 1 x 1 x 4 cm, two of each; filter - paper; two eprouvettes; Benedict solution (reacting when in contact with reducing sugars, in this case, sucrose) and iodine solutions (sensitive to starch), 2ml of each. Primarily, the two samples were samshed to form a jelly - like mass, which was then added a small amount of water, enough to rise the mass of the specimen to 2 ml. ...read more.

Conclusion

The best method for obtaining optimal mass would have been drying the samples using the laboratory dryer, with all the samples dryed at the same temperature, for the same time, though not completely extracting water from samples. Refferences * ,,Zanimljiva biologija'', I. I. Akimu�kin, 1975, Nolit, Beograd * 1 http://www.cookitsimply.com/nutritional/potatoes-white-and-skin-raw-0090-01n1354.html * www.wikipedia.com * 1 http://www.cookitsimply.com/nutritional/apples-raw-with-skin-0090-0p9003.html Suggestion on methods for the experiment As a method of comparing water potentials in two different plant tissues, I suggest one of the following, with samples of apple and potato tissues, sized 1cm3 being used as speciments analyzed in each method. 1) We should use Benedict solution, which will, after submerging the samples into the solution, react with sucrose, subjected to a certain temperature, thus testing the existence of sucrose in tissue. 2) Since iodine reacts with starch, submerging the samples into the solution would prove/dissaprove the existance of starch in tissue. 3) Finally, I suggest drying the samples in a "lab - oven", at approximatelly 150� , for around 2h, with measuring the speciment mass before and after, when we get completely dry mass. After calculating the change in percentage of mass, we would be able to deduce the tissue with higher water potential. ...read more.

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