Osmosis is the diffusion of water through a selectively permeable membrane. A selectively membrane means that the cell membrane can only control over certain things that come in and out through the membrane. A membrane is just the structure surrounding the cell. Throughout osmosis, the cell could either get larger, or smaller. If the cell gets larger it means that it was put into a hypotonic solution, and result to the cell exploding. If the cell gets smaller, it means it was put in a hypotonic solution. If nothing happens to the cell, that means it was put in an isotonic solution. Once a cell starts to get smaller, it will shrivel. The difference between osmosis and diffusion is that diffusion is the process by which molecules move from an area of high concentration to an area of low concentration.
Methods: To test, and see the difference between osmosis and diffusion, my group and I conducted three different labs. The first lab we had completed was one where you put an Elodea leaf under the microscope. As step one we put it on a microscope slide, put a few drops of water on top of it, and observed it under the microscope. As step two, we put a few drops of salted water on the leaf, and observed it underneath the microscope. Then we compared the differences in the leaf before and after. After looking at the two different images, it was clear that osmosis had taken place. The leaf in the salt water had become more shriveled; you could also see it a lot better, obvious that something had taken place.
The second lab that we had done involved carrots, and took three days to complete. We first got two cups and filled them halfway with water, in one of them we out one tablespoon of salt. After labeling the salted cup, we then took two carrots. On each carrot we tied a piece of string to it, and soaking each of them in the water. Before we could put either of the carrots into a cup, we described the textures of them. We then put Carrot 1 into the water, while Carrot B went into the salted water. After about three days, we went back and got the carrots out of the water.
Some of the observations we had noticed was that Carrot 1 had gotten sturdier, much harder. Carrot 2 on the other hand had gotten rough spots, and pretty bendy overall. Both of the carrots had gotten bigger. Knowing that osmosis had taken place, the task was now to figure out if it was hypertonic, or hypotonic. Knowing that Carrot 1 had gotten bigger, and much firmer, we knew that hypotonic osmosis had taken place. Since Carrot 2 was supposed to get smaller, we assumed that hypertonic osmosis had taken place, because the carrot was supposed to shrink and get smaller, meaning that the salt would’ve pulled out the natural waters in Carrot 2.
The third lab we had done we tested the amount of glucose that would have diffused out of the baggie. First we took a graduated cylinder and poured 15ml of prepared glucose into it. Next we took a dialysis tube that had been soaking in water and tied a knot in one end. With the unknotted end, we carefully poured the 15ml of glucose in.
After tying a knot in the open end, noting the coloring of the bag, determining if glucose was present in the tube using an indicator strip and seeing that there wasn’t any we went ahead and put 250 ml of distilled water along with one ml of potassium iodide (IKI) and the dialysis bag into our beaker. Once we had noted that inside of the dialysis bag it was clear, the beaker was brown because of the IKI, and that there was glucose inside of the dialysis bag, but not the beaker, we were ready to wait 30 minutes to move onto the next set of steps.
After the long 30 minutes, we removed the dialysis bag from the beaker. Next we recorded data from the dialysis bag which was sugar, and glucose present. The color went from clear to a light blue, and there was still glucose present. The data from the beaker had also changed, the color had stayed the same, but the glucose present had changed, because in the beginning the beaker didn’t have any glucose, but now the distilled water had some. We knew that the glucose from the dialysis bag, had come out and into the beaker, and we knew that it had to be through diffusion because it wasn’t just water in the beaker.
Results: In doing these three labs, we had learned the difference between osmosis and diffusion and we had also learned some very important vocabulary. For our first lab we had done, with the leaf, we had learned that osmosis had taken place, and because of osmosis, the leaf had expanded a lot. The leaf became more visible underneath the microscope, but with the naked eye, it had become a lot smaller, and shriveled. In this lab hypertonic osmosis had taken place, because the salt from the salt water had brought the natural waters out of the leaf, and before you knew it the leaf under the microscope was much smaller. In our second lab we had discovered that both of the carrots went through a phase of osmosis. Carrot 1 had gone through hypotonic osmosis, where the water goes through the cell membrane.
The water moves from the outside in, which explains why the carrot was bigger, and why it was much more firm than Carrot 2 which had gone through hypertonic osmosis, meaning that the salt in the cup/beaker had gone through the cell membrane, and basically soaked up the natural water in the carrot, and transferring it into the water inside the cup causing for the carrot to be shriveled up and smaller. In our third lab, we had saw diffusion for the first time. It is almost just like osmosis, except osmosis is only water and salts, and sugars. In this lab we had used potassium iodide in the water, making it not only water. The experiment had gone well, and we got the results we had wanted.
The thin dialysis bag had a certain amount of sugar in it, while the beaker it was laying in had absolutely none. In the end, the beaker had shown a significant amount of sugar in it, and because the potassium iodide could not pass through the dialysis bag, the sugar went ahead and came out of the bag, making the process of diffusion complete. Discussion: All three of these labs worked out, and ended pretty well except our second lab, the carrot lab.
Our data had shown that the weight after being soaked for three days of the carrots weren’t any different, they had both gained weight. But that had made no sense to us because the carrot that was in the salt water should’ve shrunk and not gained weight. Some of the errors that could’ve gone wrong were that we may not have put enough salt in the cup for anything to actually take place. But because we had known what was supposed to happen, we had an idea of what actually happen, and the fact that the characteristics of everything of a shrunken cell had taken place, besides the fact that the carrot had gained a little bit of weight. References: Lab Worksheets.
Cellular Transport Vocabulary
AP Bio Lab 1 Osmosis and Diffusion Lab Activity
Elodea Leaf Lab
Acknowledgements: Thank you Miss. Pagano for teaching me the difference between osmosis and diffusion and for writing up these labs to help my classmates and I understand it better and much easier!