Words: 886
Osmosis Lab Introduction: In order for cells to interact with their environment, molecules must be able to move through the cell membrane. Movement within the cell occurs by diffusion. Molecules move through the cell membrane by osmosis. Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration. This happens because of random molecular motion. Molecules move around randomly until there is an even mixture throughout cell and mixture.
The overall effect is that molecules move down a concentration gradient from a region of high concentration to a region of low concentration which is passive transport. Osmosis is the movement of molecules down a concentration gradient and at the same time through a membrane. Selectively permeable membranes only allow certain molecules to go through the membrane into or out of a cell. For example, water can cross the membrane while a salt solution cannot. If there is a concentration gradient across the membrane, water will move across the membrane down the concentration gradient while the salt cannot.
If there is more salt and less water inside a cell than outside, water will flow into the cell from the surrounding environment. This process is called osmosis. When the environment outside a cell has a lower concentration of dissolved molecules than inside the cell, the solution is hypotonic, and water will move from the solution into the cell. If the surrounding solution has a higher concentration of dissolved molecules than the cell, the solution is hypertonic. In that case, water will move from the cell out into the surrounding solution.
An isotonic solution is when the concentration of dissolved molecules is the same inside and outside the cell, and there is no net movement of water across the membrane. When cells are placed in a hypertonic solution, water flows out of them and they shrivel up. When cells are placed in a hypotonic solution, water flows into them. If the cell does not have a cell wall, it will burst in a hypotonic solution. The purpose of this lab is to observe the effect of isotonic, hypotonic, and hypertonic solutions on potato cells.
Independent variable: Sucrose concentration Dependent variable: Potato weight Hypothesis: I hypothesize that when the sucrose concentration is higher, the weight of the potato cylinders will decrease and when there is less sucrose concentration, the weight of the potato cylinders will increase. Materials: Potatoes Petri dish Scale Cork borer Beakers Wax wrap Water Sucrose solution (0. 2M, 0. 4M, 0. 6M, 0. 8M, 1. 0M) Method: 1) Get 3 of the sucrose solutions that are in beakers (either 0M, 0. 2M, 0. 4M or 0. 6M, 0. 8M, 1. M) 2) Use a cork borer to cut four potato cylinders for each beaker (a total of 12 potato cylinders since you will have 3 beakers). 3) Weigh each set of 4 potato cylinders on a scale. 4) Put 4 of the potato cylinders in each solution. 5) Cover the beakers with wax wrap. 6) Let it stand overnight. 7) Remove the potato cylinders from the solution and blot them gently on a paper towel. 8) Weigh each set of 4 potato cylinders. Data: Sucrose Concentration (M)| Mass before solution (g)| Mass after 1 day in solution (g)| Difference (g)| Percent change (%)| 0. | 3. 04| 3. 43| 0. 39| 12. 8| 0. 2| 3. 61| 3. 66| 0. 05| 1. 39| 0. 4| 3. 36| 2. 96| -0. 40| -11. 9| 0. 0| 3. 37| 4. 24| 0. 87| 25. 8| 0. 2| 2. 27| 2. 81| 0. 09| 3. 96| 0. 4| 3. 22| 2. 64| -0. 58| -18. 0| 0. 0| 5. 00| 5. 60| 0. 60| 12. 0| 0. 2| 5. 91| 6. 23| 0. 32| 5. 41| 0. 4| 5. 40| 4. 54| -0. 86| -15. 9| 0. 6| 4. 87| 3. 73| -1. 14| -23. 4| 0. 8| 4. 89| 3. 67| -1. 22| -24. 9| 1. 0| 4. 63| 3. 78| -0. 85| -18. 4| 0. 6| 5. 95| 3. 48| -2. 47| -41. 5| 0. 8| 5. 68| 4. 74| -0. 94| -16. 5| 1. 0| 3. 90| 3. 98| 0. 08| 2. 05| 0. 6| 4. 98| 3. 67| -0. 81| -16. 3| 0. | 4. 03| 2. 89| -1. 14| -28. 3| 1. 0| 4. 15| 2. 91| -1. 24| -29. 9| Sucrose Concentration (M)| Average Percent Change (%)| 0| 16. 9| 0. 2| 3. 59| 0. 4| -15. 3| 0. 6| -27. 1| 0. 8| -23. 2| 1| -15. 4| Conclusion: This lab was able to show the effects isotonic, hypertonic, and hypotonic solutions on potato cells. Osmosis was clearly shown since the potato cylinders decreased or increased at different concentrations of sucrose. The results supported my hypothesis because for the 0. 0 sucrose concentration the average percent change in mass was 16. 9%. For the 0. concentration the percent change was 3. 59%. For the 0. 4 concentration the percent change was -15. 3%. For the 0. 6 concentration the percent change was -27. 1%. For the 0. 8 concentration the percent change was -23. 2%. For the 1 concentration the percent change was -15. 4%. The reason for the change in mass is the process of osmosis. When the sucrose concentration was 0, the cores gained weight because the concentration in the potato cells was different from the concentration outside, which was a hypertonic solution. When the sucrose concentration was 0. , it was an isotonic solution, so there was no major difference in mass. When the concentrations of sucrose were higher (0. 4, 0. 6 and 0. 8), the outside solution was hypotonic because there was a decrease in the potato weight. Evaluation: One of the groups seemed to have weighed their 1M sucrose concentration incorrectly or have done something incorrectly since that data came out to be much different than the rest of the 1M sucrose concentrations from other groups. This affected the average percentage and the graph. Other than that, no errors were made in the experiment.
One improvement that could be done to the experiment would be to do the experiment multiple times in each group to get more accurate data. Also, the size of the potato cores could have been measured with more precision so that each potato core was the same weight. Another improvement could be for every group to do all the concentrations. For future studies, other types of cells could be used and more typed of sucrose concentrations could be used as well. The isotonic concentration is 0. 22M. ? = -1(0. 22 mole)(0. 0821 liter bars/mole ?? K)(297. 1K) ? = -5. 37 liter bars