Diffusion and Osmosis free essay sample

Diffusion and Osmosis Osmolarity of Plant Cells In this class, we learned about hypertonic, hypotonic, and isotonic solutions. Hypertonic solutions have a higher concentration of solutes outside of the membrane, hypotonic solutions have a lower concentration of solutes outside the membrane, and isotonic solutions have an equal amount of solutes inside and outside of the membrane (Morgan Carter, 66). When the solute concentration is not equal, the water concentration is not equal, so water will move from a higher concentration to a lower concentration in a process called osmosis. In this experiment, we cut 4 pieces of potato, weighed them, and let each soak in a different sucrose solution for about an hour and a half. Our solutions consisted of distilled water (. 0 sucrose molarity), . 1 sucrose molarity, . 3 sucrose molarity, and . 6 sucrose molarity. Our question was â€Å"which solutions are hypertonic, which are hypotonic, and which are isotonic? †. This can all be determined through weight change. We will write a custom essay sample on Diffusion and Osmosis or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page We hypothesized that distilled water would be a hypotonic solution, the . 1M would be a hypotonic solution, the . 3M would be an isotonic solution, and the . 6M would be a hypertonic solution. We thought that . M would be the isotonic solution because its molarity is in the middle. If . 3M is in fact an isotonic solution, then the water concentration is the same inside and outside of the membrane and there should be no water movement resulting in no weight change. If distilled water and . 1M are hypotonic solutions, then the concentration of water is higher on the outside, so water will move into the potato where water concentration is lower, causing a weight gain. Finally if . 6M is hypertonic, then water concentration is lower on the outside, so water will move from the inside of the potato to the solution, causing the potato to lose weight. After about an hour and a half we took the potato pieces out of the solutions they were soaking in, patted the water off of them, and weighed them for a second time. The initial weight and final weight was recorded, which can be seen in Table 1. The potato piece that was soaking in the distilled water had a 3. 1% weight gain, and the potato piece that was soaking in . 1M sucrose had a 2. 1% weight gain. The potato piece had no weight change in the . 3M sucrose solution. And the potato piece that was soaking in . 6M sucrose solution had a 5. 7% weight loss. The weight changes can be easily seen in Graph 1. Table 1: Change in Weight |Sucrose Molarity: |0M |0. 1M |0. 3M |0. 6M | |final weight (g) |16. 4 |14. 7 |17. 7 |13. 2 | |initial weight (g) |15. 9 |14. 4 |17. 7 |14 | |weight change (g) |0. 5 |0. 3 |0 |0. 8 | |%change in weight |3. 10% |2. 0% |0% |5. 70% | Graph 1: [pic] As you can see, the results supported our hypothesis. Distilled water is a hypotonic solution, which makes sense because there is no concentration of solute in it. The water moved to the potato because the potato has more sucrose concentration, meaning a lower water concentration. The potato that was soaking in . 1M sucrose solution also gained weight as an effect of having a lower water concentration inside, but its weight gain percentage was lower because the solution had more solute than the distilled water. The potato soaking in . M sucrose solution had no change because the concentration of sucrose was the same in the potato as it was in the solution, as we predi cted. The potato lost weight in the . 6M sucrose solution because the amount of sucrose inside the potato was less than the solution causing water movement from the potato to the solution. These results clearly demonstrate the process of osmosis. The water moved from a region where concentration is higher to a region where concentration is lower in every case, just like it would in a cell. Of course there is always a possibility of human error in weighing, labeling, and so on. One mistake our group made was that we forgot to look at the time when we put the potatoes in the solution, so we took them out a couple minute after the group next to us took theirs out, since we started at about the same time. When our results were compared to the results of other groups, they still seemed to match up. Repeating the experiment multiple times would give even clearer results. Diffusion of Starch, Salt, and Glucose Diffusion is when molecules move from an area where they are high in concentration to an area where they are low in concentration (Morgan Carter, 66). In this experiment, we tested the ability of certain substances to pass through a semi-permeable membrane in the process of diffusion. Our semi-permeable membrane was dialysis tubing that was presoaked in water. We tied one end of the tubing with string, filled it with a solution that contained starch, salt, and glucose, and then we tied the other end. We weighed it, so we could later weigh it to discover if there was any weight change. We then placed the dialysis tubing into a beaker of distilled water. Our question was â€Å"which of these substances would be able to pass through the dialysis tubing, or semi-permeable membrane? †. After we let the tubing soak for 30 minutes, we could test for the presence of starch, salt, and glucose using 3 tests (iodine test for starch, silver nitrate test for salt, and Benedict’s reagent for glucose). Our hypothesis was that we would find the presence of all three substances in the distilled water. We thought this because we knew that molecules naturally diffuse when surrounded with an area with less concentration, but we didn’t know how much the semi-permeable membrane would interfere. Our other hypothesis was that water would enter the tubing as substances escaped it. We thought that due to osmosis, the water would move from the area of higher concentration (outside the tubing) to the area of lower concentration (inside the tubing). If our hypothesis was correct and all substances made it through the membrane, then we would expect to see the tubing gain weight and the original distilled water test positive for each substance, using our 3 tests, after the 30 minutes. To carry out the tests we had a positive control for each substance. The positive controls allowed us to see the results of the tests when we knew the solution contained the substances being tested for. We filled 3 test tubes with the starch/salt/glucose solution (positive controls) and 3 test tubes with the distilled water that the dialysis tubing had been soaking in. We put three drops of iodine in a positive control test tube, and three drops into a distilled water test tube to test for starch. Then we put five drops of silver nitrate into a positive control test tube, and five drops into a distilled water test tube to test for salt. Lastly, we put five drops of Benedict’s reagent into a positive control test tube, five drops into a distilled water test tube, and placed them both into boiling water to test for glucose. We recorded the color of each, which can be found in Table 2. We also weighed the tubing after it had soaked for 30 minutes and recorded it with the initial weight, which can be found in Graph 2. Table 2: Results of Diffusion Tests Test tube |Initial color |Final color | |starch pos control |cloudy, white |dark purple | |starch experiment |clear |yellow | |salt pos control |cloudy, white |cloudy, white | |salt experiment |clear |cloudy, white | |glucose pos control |cloudy, white |orange | |glucose experiment |clear |orange | Graph 2: [pic] If we look at Table 2 we see that we got the same color in the distilled water as we got in the positive control for the salt test and the glucose test, meaning that the distilled water tested positive for those substances. For the starch test, the positive control turned dark purple, but the distilled water turned yellow, meaning that it tested negative. If these results are correct, then starch was unable to pass through the semi-permeable membrane. This made our hypothesis false, but not completely. We were still correct about the salt and the glucose making it throught the membrane. Our other hypothesis was correct. Graph 2 displays a weight gain showing that osmosis occured, like predicted. Just like with every experiment, there is room for human error. In this experiment, a mistake that could easily be made is with tying the ends of the tubing and making sure there is no leaks. That mistake could even go unnoticed leading to false results, because it makes it look like the substances made it through the membrane when in actuallity the substances accidently spilled into the distilled water. I think these experiments were successful in demonstrating diffusion and osmosis. The diffusion experiment clearly showed that substances move down a concentration gradient until concentration is equal everywhere, unless something is holding the substances back, like a membrane. The osmosis experiment showed that water always moves down its concentration gradient also. They both showed a search for balance, or equilibrium, on a level that is hard to see without investigation. References Morgan, J. G. and M. E. B. Carter. 2013. Energy Transfer and Development Lab Manual. Pearson Learning Solutions, Boston, MA.    |Points |Self-Assessment |Total Earned | |Introduction |2 |  2 |   | |Results |2 |  2 |   | |Figures/Tables |3 |  3 |   | |Discussion |3 |  3 |   | |Total |10 |  10 |   |