Diffusion, Osmosis, and Water Potential Lab Report Activity A: Diffusion Background: Diffusion is the movement of molecules from areas of higher concentration to areas of lower concentration. Two specific kinds of diffusion are active transport and passive transport. Active transport is the movement of molecules through a cell membrane through processes that require the use of energy. Passive transport is the movement of molecules through a cell membrane without the use of energy. Question: If starch solution is placed inside a semi-permeable membrane which is surrounded by distilled water with IKI solution, in what direction will the molecules move? Hypothesis: The factors of this experiment which are to be controlled, are the amount of distilled water and IKI solution that are in the beaker, the size of beaker, the amount of sucrose solution in the dialysis tube, the size of the dialysis tube, and the time each dialysis tube is submersed in the beaker. Throughout this experiment we will look for any color change in the beaker or dialysis bag and therefore, will be taking qualitative measurements. The independent variables are the different concentrations of Starch solutions. The dependent variables are the initial and final colors of the solutions. If a dialysis tube with starch solution in it, is placed in a beaker filled with distilled water and IKI solution, a color change, of purple or blue, in the beaker will be observed. Materials: Dialysis tubing, beakers, starch solution, distilled water, iodine-potassium iodine (IKI) solution, dropping pipette, glucose test strips, funnel. Procedure: Control Test 1. Pour 5 ml of distilled water into the test tube labeled IKI. Add approximately 5 ml of IKI solution to the water and mix well. Be aware that the IKI solution can irritate the skin, mouth, and eyes, and can stain skin or clothing. Record the solution color in Table1. 2. Pour 5 ml of distilled water into the test tube labeled Starch. Add approximately 5 ml of Starch solution to the water and mix well. Record the solution color in Table 1. 3. Pour 5 ml of distilled water into the test tube labeled Starch + IKI. Add approximately 5 ml of Starch solution to the water and mix well. Add approximately 5 ml of IKI solution to the water and mix well. Record the solution color in Table 1. Diffusion Test 4. Obtain a piece of dialysis tubing that has been soaked in water. The tubing should be soft and pliable. Roll the tubing between your thumb and index finger to open
it. Close one end of the tube by knotting it or tying it off with string. This will form a bag. 5. Using a small funnel, pour 15 ml of starch solution in the dialysis bag. Smooth out the top of the bag, running it between your thumb and index finger to expel the air. Tie off the open end of the bag. Leave enough room in the bag to allow for expansion. Record the initial color of the solution in the bag in Table 2. 6. Pour 160-170 ml of distilled water into a beaker. Add approximately 4 ml of IKI solution to the water and mix well. Record the initial color of the solution in the cup in Table 2. 7. Immerse the dialysis bag in the solution in the cup. Make sure that the portion of the bag that contains the starch solution is completely covered by the solution in the cup at all times. 8. Record the color of the solution in the cup in Table 2. 9. Wait 30 minutes. Record final colors of the solutions in Table 2. Results: Table 1: Control Test IKI Starch Starch + IKI Color of Solution Golden Clear Dark blue, near black brown/yellow Table 2: Diffusion Test Inside the Dialysis Tubing Inside the Beaker Initial Color of Solution Clear Light yellow Final Color of Solution Dark purple/ blue Light yellow The final color of the solution inside of the dialysis tubing was the same color, dark purple/blue, as when starch and IKI were added together in the Control Test. The color of the solution inside the beaker was the same during the Control Test, a shade of yellow. Conclusions: Based on the data we collected, our hypothesis was proved incorrect. Our hypothesis stated that the color change would occur in the beaker but it occurred in the dialysis tubing. This information tells us that the IKI solution had a higher concentration and therefore diffused into the starch solution which had a low concentration of molecules. One possible source of error that may have occurred during this experiment, was that there may have been air bubbles that weren t expelled before the dialysis bag was tied off. Another possible source of error was that though the dialysis bags were measured at the same size, when tied off, they were tied off unequally. Evaluation: This procedure was successful in that it allowed you to compare the final results with the control test. It was also successful as the final colors of the solution were very clear in their meaning. This was a fairly simple experiment and the procedure was easy to follow and as such, needs no major changes.
Activity B: Osmosis Background: Osmosis is the diffusion of water molecules across a semi-permeable membrane. Solutions which have the same solute concentration are called isotonic. A solution which has a higher solute concentration than another solution is called hypertonic. A hypotonic solution is a solution which has a lower solute concentration than another solution. Water will move in whichever direction has a higher solute concentration because that solution will have a lower water concentration and water has its own concentration gradient. Question: If different concentrations of sucrose solution are placed inside a semipermeable membrane which is surrounded by distilled water, in what direction will the water move? Hypothesis: The factors of this experiment which are to be controlled, are the size of beaker, the amount of sucrose solution in the dialysis tube, the size of the dialysis tube, and the time each dialysis tube is submersed in the beaker. Throughout this experiment we will look for any change in the mass of the dialysis bags and therefore, will be taking quantitative measurements. The independent variable is the different concentrations of sucrose solutions. The dependent variables are the initial and final masses (g) of the dialysis bags. If the molar concentration of sucrose becomes increasingly higher, then the dialysis bag will have an increasingly higher mass. Materials: Dialysis tubing, beakers, distilled water, funnel, sucrose solutions, balance Procedure: 1. Pour ~150 ml of distilled water into a beaker. Label the beaker with the concentration of sucrose that will be tested. 2. Obtain a piece of dialysis tubing that has been soaked in water. The tubing should be soft and pliable. Roll the tubing between your thumb and index finger to open it. Close one end of the tube by knotting it or tying it off with a piece of string. This will form a bag. 3. Using a small funnel, poor ~15 ml of sucrose solution into the dialysis bag. Smooth out the top of the bag, running it between your thumb and index finger to expel the air. Tie off the open end of the bag. Leave room in the bag for expansion. 4. Dry the bag gently with a paper towel and then determine its mass. Record this as the initial mass in Table 3. 5. Immerse the dialysis bag in the water in the beaker. Make sure that the portion of the bag that contains the sucrose solution is completely covered by the water in the cup at all times. Wait 30 minutes before continuing to the next step. 6. After 30 minutes, remove the bag from the beaker and dry it gently with a paper towel. (It should be as dry as it was before you measured the initial mass.) Mass the bag and record the final mass in Table 3. Finally, determine the change in mass of the bag and record this data in Table 3.
Results: Table 3: Osmosis Test Contents in Dialysis Bag 0.0 M 13.02 13.11 0.09 0.69 0.31 (Distilled Water) 0.2 M 12.93 13.69 0.76 5.8 5.27 0.4 M 13.95 15.35 1.4 9 11.35 0.6 M 15.25 17.34 2.09 13.7 14.66 0.8 M 15.47 18.15 2.68 17.32 16.22 1.0 M 15.87 19.33 3.46 21.8 21.68 The data shows an increase in the change in mass as the molar concentration of sucrose increases. It also shows that the class average of the percent change in mass was lower than our group s data during the 0.0 M, 0.2 M, 0.8 M, and 1.0 M tests. During the 0.4 M, and 0.6 M tests however, the class average was higher. Graph 1: Osmosis Test 25 20 15 10 5 0 Initial Mass (g) Final mass (g) Change in Mass (g) Your % Mass Initial Mass (g) Change in Mass (g) Your % Mass Class Average of % Mass Class Average of & Mass Conclusions: The results of this experiment supported our hypothesis, which stated that the higher the molar concentration of sucrose, the more the bag would weigh. The data collected showed this by the increase in the change in mass. This information tells us that the sucrose solution in the dialysis bag had a higher solute concentration than the beaker solution, and was therefore hypertonic. Because it was hypertonic, it had a lower water concentration while the beaker solution had a higher water concentration. The water, through osmosis, therefore moved from the beaker into the dialysis bag. One possible source of error, once again, that could have occurred, was for air bubbles to be trapped in with the dialysis bag solution. Also, another possible source of error could have been a mistake in the measuring of weight. The 0.0 M sucrose solution may have been initially weighed incorrectly which may attribute to it having a greater percent change in mass.
Evaluation: This procedure was successful in that it was simple and easy to follow. It also was successful as it led to clear results. The procedure was very specific in its directions which greatly limited any potential error. Activity C: Potato Diffusion; Water Potential Background: Water potential is the quantification of the tendency of water to diffuse from one area to another. The net movement of water is always from an area of high water concentration to an area of low water concentration. It is used to predict the direction that water will move through the use of an equation. = S + P or Water Potential = Solute Potential + Pressure Potential Question: If a potato cylinder is placed inside different concentrations of sucrose solutions, in what direction will the water move? Hypothesis: The factors of this experiment which are to be controlled, are the size of beaker, the amount of sucrose solution in the beaker, and the time each potato cylinder is submersed in the beaker. Throughout this experiment we will look for any change in the mass of the potato cylinders and therefore, will be taking quantitative measurements. The independent variable is the different concentrations of sucrose solutions. The dependent variables are the initial and final masses (g) of the potato cylinders. No hypothesis was formed in advance. Materials: Beakers, balance, distilled water, cork borer, sucrose solution, potato Procedure: 1. Pour 100 ml of the assigned sucrose concentration solution into a labeled beaker. 2. Use a cork borer (approximately 5 mm in inner diameter) to cut six potato cylinders. Cut each cylinder to approximately 1 cm in length. Do not include any skin on the cylinders. 3. Keep your potato cylinders in a dry, covered beaker until it is your turn to use the balance. 4. Determine the mass of the six cylinders separately and record the initial masses in Table 4. Put the six cylinders into the separate beakers containing the different concentrations of sucrose solution. 5. Cover the cup with plastic wrap to prevent evaporation. 6. Let stand overnight. 7. The next day, record the temperature of the liquid in the cup in Table 4. It will be used later in calculations of osmotic potential. 8. Remove the cores from the beakers, blot them gently on a paper towel, and determine their masses. 9. Record the final masses in Table 4 and calculate percent change in mass.
Results: Table 4: Potato Diffusion Test Contents in Beaker Initial Mass Final Mass Change in Mass % Change in Mass Temp. (Kelvin) 0.0 M 0.69 0.86 0.17 24.63 25 (Distilled Water) 0.2 M 0.69 0.66-0.03-4.35 25 0.4 M 0.69 0.48-0.21-30.43 25 0.6 M 0.69 0.37-0.32-46.37 25 0.8 M 0.69 0.40-0.29-42.03 25 1.0 M 0.82 0.47-0.35-43.68 25 Graph 2 (Part 1): Potato Diffusion Test 1 0.8 0.6 0.4 0.2 0-0.2 Initaial Mass Final Mass Change in Mass % Change in Mass -0.4-0.6 Graph 2 (Part 2): Potato Diffusion Test 30 20 10 0-10 -20 1 2 3 4 5 6 % Change in Mass Temperature -30-40 -50
Table 5: Water Potential Concentrations Water Potential = S + P 0.0 M = (1 0.0 0.831 25) + 0 = 0 0.2 M (1 0.2 0.831 25) + 0 = 4.15 0.4 M (1 0.4 0.831 25) + 0 = 8.31 0.6 M (1 0.6 0.831 25) + 0 = 12.46 0.8 M (1 0.8 0.831 25) + 0 = 16.62 1.0 M (1 1.0 0.831 25) + 0 = 20.77 Graph 3: Water Potential 25 20 Water Potential 15 10 Water Potential 5 0 0.0 M 0.2 M 0.4 M 0.6 M 0.8 M 1.0 M This data shows a decrease in the change in mass in all the solutions with sucrose (not 0.0 M sucrose). In the distilled water test though, the change in mass increases. Also, the water potential increased at a steady, linear rate as the sucrose concentration increased. Conclusions: Despite not having a hypothesis, the results of this experiment showed that change in mass was generally negative, or in other words, water diffused from the potato into the beaker solution. The reason that this occurred in the 0.2 1.0 sucrose solutions is that there was a higher concentration of starch in the solution than in the potato, making the potato hypotonic. In the 0.0 M sucrose solution however, this was not the case because there was a higher concentration of starch in the potato, making it hypertonic. One possible method of error that could have occurred, was the incorrect measuring the potato cylinder. This could have occurred to the potato cylinder used in the 0.6 M sucrose solution as the percent change in mass was slightly larger than it should have been.
Evaluation: This procedure was fairly explanatory but could have been better in describing how to find the water potential. It was successful however, in providing clear results as to how the diffusion occurred.