Running Head: ESTIMATING OSMOLARITY 1

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1 Running Head: ESTIMATING OSMOLARITY 1 Lab Report on Estimating Osmolarity of Potato cells by Change in weight Name Class Instructor Date

2 ESTIMATING OSMOLARITY 2 Abstract This experiment was carried out with an aim of estimating the Osmolarity of potato cells by weight. The materials used were 7250ml beakers, a razor blade, a metric ruler, a balance, Petri dish, a metric ruler, aluminum foil, paper towels, forceps, sharpie, one large potato tuber, 0 molar deionized water and sucrose solutions ( 0.1, 0.2, 0.3,0.4, 0.5 and 0.6M). The potato cylinders were cut it pieces of length 5cm and replaced in sucrose solution and salt solution of different Morality. They were then removed and weighed. The procedure was repeated several times until all samples were weighed in the chronological order. Two tables were constructed, one for salt solution and the other for sucrose. A graph of percentage change in mass against concentration of solutions was constructed. It was found that, salt had greater osmotic effect than sucrose. In table 1, the percentage change in mass decreased from 9.72% to -2.67% as sucrose concentration increased from 0.0M to 0.6M. The Osmotic concentrations were grater than zero in sucrose solution of 0.0M, 0.1M, 0.2M,0.3M and 0.4M meaning that these cells were hypertonic. On the other hand, the osmotic concentrations were less than zero in sucrose solution of 0.5M and 0.6M signifying that, these cells were hypotonic.in table 2, the percentage change in mass decreased as the concentration of salt solution increased. Osmotic concentrations were grater than zero in salt solution of 0.0M, 0.1M and 0.2M meaning that these cells were hypertonic. On the other hand, the osmotic concentrations were less than zero in salt solution of 0.3M, 0.4M, 0.5M and 0.6M signifying that these cells were hypotonic. Using the graph constructed, the Osmolarity of salt was found to be 0.27M while that of sucrose was found to be 0.54M.

3 ESTIMATING OSMOLARITY 3 Introduction According to Baumgarten and Feher (1998), osmosis has been experimented from 1700s to 1870s. Nevertheless, it s cause is still being disputed by biologists (p.216). In attempt to explain its cause, a model based on water concentration was put forward (Weiss, 1996). Salisbury and Rose (1992) observed that the addition of solute to a solution reduces water concentration (p.39). Wolf, Brown and Prentiss (1982) points out that, sucrose solution (955g/L) containing 2.0 Morality has less water concentration than a salt (NACL) solution of 0.2 Morality. The maintenance of a constant state of cell is attained by regulating the movement of materials across cell cytoplasm, organelle and plasma membranes (Weiss, 1996). Wolf et al argues that both the external cell environment and cytoplasm contain water (a solvent) and many inorganic and organic materials which act as solutes. The membranes of organelle and plasma are semipermeable which permit easy movement of water but controls solutes movement across the cell. These movements of materials across the cell membranes are aided by energy packet called Adenosine Triphosphate abbreviated as ATP (Weiss, 1996). However, some materials do not depend on ATP to move across the membrane provided the cell membrane permits them to pass through. Salisbury and Rose (1992) defines osmosis as the movement of water molecules from a region of high concentration to a region of low concentration through a semi-permeable membrane. When one side of a cell membrane has a higher concentration than the other, a concentration gradient is created which allow movement of water from where the concentration is high to where the concentration is low(weiss, 1996)). Those substances which experience this phenomenon are referred to as Osmotically Active Substances abbreviated as OAS. Hypertonic solution is a solution in which it has greater Osmolarity than the solution on the other side of the membrane. Hypotonic solution is a solution which has a lower Osmolarity than the other side of

4 ESTIMATING OSMOLARITY 4 the membrane. However, isotonic solution is solution which both side of the membrane has equal or same Osmolarity (Weiss, 1996). The aim of this experiment is to estimate the Osmolarity of potato cells by change in weight. Materials and Methodology To carry out this experiment, the following materials were used: 7250ml beakers, a razor blade, a metric ruler, a balance, Petri dish, a metric ruler, aluminum foil, paper towels, forceps, sharpie, one large potato tuber, 0 molar deionized water and sucrose solutions ( 0.1, 0.2, 0.3,0.4, 0.5 and 0.6M) Seven beakers were labeled 0.0M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M and 0.6M. 100Ml of the sucrose solution was added to the correct beaker. Seven undamaged potato cylinders of length 5cm were obtained using a sharp cork borer. The potato cylinders were lined up and cut into a uniform length of 5cm while removing the peel from the end. They were then put into a Petri dish and kept covered to prevent them from drying out. The potato cylinders were then removed from the Petri dish and placed between paper folds of a paper towel in order to blot the sides and end. The potato cylinders were weighed to the nearest 0.001grams by placing them on the aluminum sheet on the balance. The weight was then recorded in the table in the result section. After being weighed, the cylinders were immediately cut lengthwise into two long halves and then transferred into the beaker containing water and time noted and recorded. Steps 6 and 8 were repeated with each cylinder, placing potato cylinders in appropriate incubating solution ranging from 0.1 and 0.6M. Incubation was then done for one and a half hours. The beaker was swirled after every 10 to 15 minutes as the potato cylinders incubate. The time when the potato cylinders were removed at the end of the incubation period and the total

5 ESTIMATING OSMOLARITY 5 time the incubation took was recorded in Table 1. The potato pieces were removed from the first sample and blotted on a paper towel removing the excess solution only. The potato pieces were then weighed and the final weight recorded in table 1. The procedure was repeated until all samples were weighed in the chronological order in which they were originally placed in the test solution. The sucrose solutions were replaced with salt solutions and the procedure repeated. All the data was recorded in the result section. Results Figure 1 Table Showing Sucrose Morality, Final weight, Initial weight, Weight change and Percentage change in weight Sucrose Morality Final Weight Initial Weight Weight Change % Change in weight As the above table shows, the percentage change in mass decreased from 9.72% to % as sucrose concentration increased from 0.0M to 0.6M. The Osmotic concentrations were grater than zero in sucrose solution of 0.0M, 0.1M, 0.2M,0.3M and 0.4M meaning that these cells were hypertonic. On the other hand, the osmotic concentrations were less than zero in sucrose solution of 0.5M and 0.6M signifying that, these cells were hypotonic.

6 ESTIMATING OSMOLARITY 6 Figure 2 Table Showing Salt Morality, Final Mass, Initial Mass, Mass change and Percentage Change in Mass of potato cylinders Salt Morality Final Mass(g) Initial Mass(g) Mass Change(g) % Change in Mass As the above table shows, the percentage change in mass decreased as the concentration of salt solution increased. Osmotic concentrations were grater than zero in salt solution of 0.0M, 0.1M and 0.2M meaning that these cells were hypertonic. On the other hand, the osmotic concentrations were less than zero in salt solution of 0.3M, 0.4M, 0.5M and 0.6M signifying that these cells were hypotonic.

7 ESTIMATING OSMOLARITY 7 Figure 3 Graph of Percentage Change in Mass against Concentration of Solutions As the above graph shows, salt (which is an ionizing substance) has greater osmotic effect than sucrose (which is not ionizing substance). This is because 1 molar concentration of complete dissociated salt will have an Osmolarity of 2osmo/L. On the other hand, I molar concentration of complete dissociated sucrose will have 1osmol/L. From this graph, the Osmolarity of salt is 0.27M (Where the salt line cuts the X-axis) while the Osmolarity of sucrose is 0.54M (Where the sucrose line cuts the X-axis) Discussion The potato tissues were used to estimate the relative osmotic concentration by measuring their percentage mass change. As sucrose concentration increased from 0.0M to 0.6M in table 1, the percentage change in mass of potato tissues decreased from 9.72% to -2.67%. The Osmotic concentrations were grater than zero in sucrose solution of 0.0M, 0.1M, 0.2M,0.3M and 0.4M

8 ESTIMATING OSMOLARITY 8 meaning that these cells were hypertonic. On the other hand, the osmotic concentrations were less than zero in sucrose solution of 0.5M and 0.6M signifying that, these cells were hypotonic. In table 2, the percentage change in mass decreased from 8.37% to % as the concentration of salt solution increased from 0.0M to 6.0 M.The Osmotic concentrations were grater than zero in salt solution of 0.0M, 0.1M and 0.2M meaning that these cells were hypertonic. On the other hand, the osmotic concentrations were less than zero in salt solution of 0.3M, 0.4M, 0.5M and 0.6M signifying that these cells were hypotonic. The graph showed that, salt (which is an ionizing substance) had greater osmotic effect than sucrose (which is not ionizing substance. The Osmolarity of salt was found to be 0.27M while that of sucrose was found to be 0.54M (estimating from the graph). Conclusion The experiment was successful since its aim was achieved. The experiment found out that salt has greater osmotic effect when compared to sucrose. Due top experimental errors while carrying out this experiment, my figures were a bit different compared to that of other experiments done on the same topic. The osmolarity of salt in this experiment is 0.27M and that of sucrose 0.57M.

9 ESTIMATING OSMOLARITY 9 References Baumgarten, C. M. and J. I. Feher (1998). Osmosis and the regulation of cell volume. Pp in N. Sperelakis (Ed.), Cell Physiology Source Book, 2nd Ed. Academic Press, San Diego, 1095 pp. Salisbury, F.B. and C.W. Ross (1992). Plant Physiology, 4 th Ed. Wadsworth Publishing Co., Belmont, CA. Weiss, T.F. (1996). Cellular Biophysics, Vol. 1: Transport. MIT Press, Cambridge, MA. Wolf, A.V., M.G. Brown and P.G. Prentiss (1991). Concentrative properties of aqueous Solutions: Conversion tables. Pp D227-D276 in R.C. West and M.J Astle, CRC Handbook of Chemistry and Physics, CRC Press, Boca Raton, Florida