Figure 1: Slicer used to obtain pieces of potato with equal surface area What is the internal solute concentration of potato cell cytoplasm? There is no net movement of water across a semi permeable membrane between isotonic solutions Potato (Solanum tuberosum) cells placed into hypertonic solutions will lose water through osmosis and potato cells placed into hypotonic solutions will gain water through osmosis. The point at which the potato cell neither gains nor loses mass (water) is the point at which the solution is isotonic to the potato cell’s cytoplasm. Testing the Osmosis Model with Solanum tuberosum to Determine the Solute Concentration of Potato Cell Cytoplasm Research Question Prediction Model Like all living things, cells require nutrients for energy and materials as building blocks. Cells also produce waste from metabolic reactions which could be toxic unless eliminated. Solutes dissolved in external cellular fluids and internal cellular fluids (cytoplasm) may enter or exit the cell through the process of diffusion. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. Osmosis is the diffusion of water across a selectively permeable membrane. Water diffuses from hypotonic (lower concentration of solutes) solutions to hypertonic solutions (higher concentration of solutes). Therefore, a cell placed into a hypertonic solution will lose water to the surrounding solution and a cell placed into a hypotonic solution will gain water from the surrounding solution. The purpose of this investigation is to test the osmosis hypothesis while determining the internal solute concentration of potato (Solanum tuberosum) cell cytoplasm. Introduction Cut 512 pieces of potato of similar size without skin. Record the mass of each piece of potato. Place the potato pieces into individual test tubes. Add 0% NaCl solution to ¼ of the samples (128 test tubes). The volume should be sufficient to adequately submerge the entire piece of potato. Repeat step 4 and 5 with 1%, 2% and 3% solutions. After 24 hours, remove the potato pieces from each solution. Gently blot each potato piece with a paper towel and immediately record its mass. WASH and dry the test tubes. Methods Figure 2: All potato pieces were measured with an electronic balance Results Figure 3: Mean percent change in mass of potato pieces as a function of NaCl concentration. At 0% change in mass (see red circle), the solute concentration is equal to 1.5 % NaCl. Error bars are 95% confidence intervals. Table 1: ANOVA results for mean percent change in mass of potato pieces in NaCl solutions of 0%, 1%, 2%, and 3%. Statistics Conclusion The purpose of this study was to use the osmosis Model to determine the solute concentration of potato cell cytoplasm. We predicted that the concentration of potato cell cytoplasm would be equal (isotonic) to the surrounding solute concentration when the potato ceases to gain or lose mass. The mean percent change in mass of potato pieces placed into 0% and 1% NaCl solutions was a positive change (gained mass) and the mean percent change in mass of potato pieces placed into 2% and 3% NaCl solution was negative (lost mass). These data imply that the solute concentration of the potato cell’s cytoplasm was somewhere between 1% and 2%. A scatterplot of the mean percent change in mass as a function of solute concentration was used to estimate the concentration of potato cell cytoplasm. The trend line crossed the x axis at 1.5%, which was zero percent change in mass; therefore the point at which the internal and external solutions are isotonic. These results provide support for the osmosis hypothesis, which states that water will move cross a semi- permeable membrane from hypotonic solutions to hypertonic solutions. The cell membrane can selectively allow certain molecules to enter or exit through diffusion (passive transport). It can also move substances across itself against a concentration gradient (active transport), which requires energy in the form of ATP. These processes allow the cell to maintain fluid homeostasis. References F.H. Knight