Osmotic Potential Lab - This is a properly formatted lab report. The subject tested was potato and this PDF

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This is a properly formatted lab report. The subject tested was potato and this lab focused on osmosis through membranes. This lab focuses on the material of cell walls as well as osmosis itself, and includes a works cited page and well-presented experiment information. ...

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SBI4U October 8th, 2017 Osmotic Potential Introduction: This experiment will investigate the trends in osmotic potential in biological systems. Osmosis takes place in all living cells. It is the movement of water from an area of high water concentration to an area of low water concentration relative to the solute concentrations on each side of a semi-permeable membrane. Semi-permeable membranes allow only water to pass between them. When comparing two fluids on either side of a semipermeable membrane, a hypotonic solution refers to a solution that has less solutes comparatively to water, and a hypertonic solution refers to a solution that has more solutes comparatively to water. In a situation where a hypertonic and hypotonic solution are on either side of a semi-permeable membrane, the osmotic potential will be higher in the hypertonic solution, as the hypertonic solution has a lower concentration of water respectively. Water will travel from the hypotonic solution to the hypertonic solution until the fluids reach tonicity, meaning equal osmotic potential, resulting in a system of equilibrium. Once the system has reached equilibrium, the water will not travel anymore. Biological systems rely on having specific concentrations of solutes inside cells depending on the water demand of that cell. Plants in particular require the root to have a higher concentration of solutes than the soil outside of the semi-permeable membrane in order to have water diffuse into the plant to survive. This is true for the plant Solanum tuberosum, commonly known as potato. The purpose of this lab is to examine osmotic potential in a potato. This will be achieved by modifying the concentration of salt water solution outside the potato per trial. A small piece of potato will be placed in a test tube of salt water solution of varying concentrations. The potato will be left to sit in the solution for two hours, and then it will be removed. The initial mass will be compared with the final mass of the potato in order to calculate how much water was gained or lost from the potato piece due to osmosis. It is anticipated that the potato piece will lose more mass in solutions with a higher concentration of salt than in solutions with a lower concentration of salt. In systems with a higher salt concentration, the fluid containing the salt will be hypertonic to the fluid inside the potato piece, and so the water will flow out from the potato cells, through the semipermeable membranes, and into the salt water solution until the system reaches equilibrium. Materials: test tube rack x12 test tubes 10mL graduated cylinder 120mL salt water solution (0%, 0.75%, 1.5%, 2.25%) potato paper towel

Procedure:

sharp knife milligram electronic scale stopwatch plastic wrap marker tweezers ruler

1) Using knife, peel skin off potato and cut out 12 rectangular potato pieces roughly 2.5 x 0.7cm in dimension. 2) Measure 10mL of water in a graduated cylinder and place in a test tube. Repeat this step for two more test tubes. 3) Measure 3 potato pieces with scale and record the mass. Place one measured potato piece in each test tube with a solution. 4) Cover test tubes with plastic wrap and label test tube with marker accordingly to the mass of potato piece in each test tube. Let sit for two hours. 5) After two hours, remove potato pieces with tweezers and pat dry with paper towel. Measure and record the mass of the 3 potato pieces with the scale. 6) Rinse out test tubes. 7) Repeat steps 2-6, substituting water for 0.75%, 1.5% and 2.25% salt water solutions. Observations: Table 1: The Change in Mass of a Potato Piece after being Soaked in 10 mL of Varying Salt Concentrations for 2 Hours Change in Mass (%) Salt Concentration (%)

Trial 1

Trial 2

Trial 3

Average

0.00

25.3

-0.02

9.57

11.6

0.75

-2.89

-0.79

-2.26

-1.98

1.50

-7.12

-11.1

-10.1

-9.44

2.25

-10.2

-14.3

-8.02

-10.8

Figure 1: The Average Percent Change in Mass of a Potato Piece after being Soaked in Varying Concentrations of Salt Solutions for Two Hours Discussion: The purpose of this experiment was to investigate trends in osmotic potential. This was done by examining osmosis in a potato. Potato pieces were placed in test tubes containing solutions of varying salt concentrations for two hours, and then the initial mass was compared with the final mass of the potato to determine whether water was gained or lost due to osmosis. It was predicted that the potato piece would lose more mass in solutions of higher salt concentration than that in lower concentrations, because the solution will be hypertonic to the fluid inside the potato in higher salt concentrations, and will therefore have higher osmotic potential, causing water to transport from the potato and into the salt water concentration until the system is isotonic. This lab proves the hypothesis was correct, as figure 1 displays the final mass of the potato decreasing by percentage as the salt water concentration increases. In Figure 1, it illustrates that in salt water concentrations of 0%, the potato piece gained mass. This is because in 0% systems, the concentration of solutes to water is greater inside the potato than outside, resulting in higher osmotic potential inside the potato. The water from the solution will travel through the semipermeable membranes of the potato cells until the fluids are of equal tonicity. This information is evidence that osmosis occurs to establish isotonic equilibrium. In Figure 1, an inverse relationship between the percent change in the mass of the potato and the salt water concentration can be observed. As the salt concentration increased, the percent change decreased, meaning the final mass was less than the initial mass of the potato. This suggests that as the salt concentration increased, the solution went from hypotonic in 0% concentrations, to hypertonic in all other tested salt water concentrations. It is evident that the other tested salt water concentrations were hypertonic because the average change in mass in those trails were all negative, as seen in Figure 1, meaning that the final potato mass was

lighter than the initial potato mass. The explanation for the final mass being lighter is that the water moved from inside the potato to the salt water solution until the system reached equilibrium, directly following the principles of osmosis. This information further proves that osmosis takes place to establish isotonic equilibrium, and does not have a preference of travelling direction through a semipermeable membrane. In conclusion, this lab revealed that the increase of solute concentration creates a trend in osmosis, as the rate of osmosis increases in systems with higher solute concentrations on one side of a semipermeable membrane to reach tonicity. It would have been more definitive to use smaller increases of salt concentration to determine the exact concentration that isotonic potential exists in without the system having to go through osmosis first, however this lab did affirm that isotonic potential is in concentrations somewhere between 0.01% and 0.74%. Being knowledgeable about the trends in osmosis is useful tool to have. Osmosis works until a system involving a semipermeable membrane reaches equilibrium in tonicity, regardless of whether the water is being taken from inside the cell or from the fluids outside the cell. Cells can die due to osmosis, as when the concentration of solutes outside the cells is higher, resulting in higher osmotic potential, this causes the water from the cells to travel outside the cell, whether water was vital to the cells survival or not. This information can be applied to weed killing, as if unwanted plants are surrounded in solutions with a high solute concentration, this will kill the plants without introducing harmful chemicals into the environment.

Appendix A: Calculation Used to Calculate Average for Table 1:

Calculation Used to Calculate Change in Mass for Observations:...