Osmosis Lab Report
Abstract
Evaluating how osmosis and diffusion occur in simulated labs can further our knowledge on how they really occur in a human body. Osmosis is the the passage of water across a membrane from an area of high concentration to an area of low concentration. Diffusion is when molecules move outward of the cell to reach an equilibrium of molecules inside and out of the cell. Osmosis and diffusion are very similar in the basics of what happens, but the difference occurs where diffusion uses molecules in an atom whereas osmosis deals with passage of water across a membrane.
Introduction
When done properly, we observed pretty drastic weight changes with both diffusion bags and the sweet potato used to simulate diffusion and osmosis. Because the diffusion bags will be sitting in different levels of sucrose molarity, we can determine there will be differences observed in every situation. The same statement could be said about the sweet potato used in the second lab performed. Both osmosis and diffusion will be demonstrated well using both the diffusion bags and the sweet potato.
Methods
This study was conducted at New Tech High School, in Kim Wootton’s Biology classroom, on September 25th, 2014. On day one of our experiment we used six strips of dialysis tubing and six types of water with different amounts of sucrose, on of them being distilled water as our control group. Our first step was tying one end of the tubing and then pouring in 20 mL of distilled water, and then tying the other end of the tube. We did this water that contained 0.2M, 0.4M, 0.6M, 0.8M, and 1.0M of sucrose. Once all the tubes were secured we recorded their weight and then placed each tube in a beaker filled with water for twenty minutes. Once we reached the end of the twenty minutes we took the tubes out of the beakers and measured it once again so that we could find the percent change in mass.
On the second day our experiment we decided to test how different solutions with sucrose would react to cores from a sweet potato. First we filler six beakers with 20 mL of water, each with a different amount of sucrose, 0.2M, 0.4M, 0.6M, 0.8M, and 1.0M as well as distilled water. Then we cut the core of a sweet potato until we had seven pieces that were the same size. We recorded the weight of each piece before placing six piece in the beckers and placing one on a paper towel so that we would have a control to compare our data to. We then waited twenty minutes so that the pieces had enough time in the beaker. We then took out the pieces individually and dabbed them on paper towels so that we wouldn’t get any excess water altering the weight. Once we weighed all the pieces of sweet potato we recorded our findings, and found the percent change in mass.
Results
For day one, we had 6 strips of dialysis tubing with different solutions in each bag. The first bag had just distilled water that had an initial mass of 37.8 g and after the 20 minutes, the mass had increased .5% (2 g). The second bag had 0.2 M of sucrose that had an initial mass of 39.7 g and after 20 minutes, the mass had increased 3.52% (1.4 g). The third bag had 0.4 M of sucrose that had an initial mass of 39.0 g and after 20 minutes, the mass had increased 5.13% (2.0 g). The fourth bag had 0.6 M of sucrose that had an initial mass of 34.6 g and after 20 minutes, the mass had increased 7.23% (2.5 g). The fifth bag had 0.8 M of sucrose that had an initial mass of 42.6 g and after 20 minutes, the mass had increased 11.27% (4.8 g). The second bag had 1.0 M of sucrose that had an initial mass of 48.2 g and after 10 minutes, the mass had increased 5.8% (2.8 g).
For day two, we had 7 pieces of a sweet potato which we soaked in different solutions for 25 minutes each. The potato on the paper towel had a decrease in mass from 2.5 g to 2.3 g. The second potato was soaked in distilled water with an initial mass of 2.3 g and after the time passed, the mass increased 4.35% (.1 g). The third potato was soaked in a blue solution with an initial mass of 1.9 g and after the time passed, the mass increased 5.26% (.1 g). The fourth potato was soaked in a purple solution with an initial mass of 1.9 g and after the time passed, the mass increased 10.53% (.2 g). The fifth potato was soaked in a yellow solution with an initial mass of 2.1 g and after the time passed, the mass increased 4.76% (.1 g). The sixth potato was soaked in a green solution with an initial mass of 2.4 g and after the time passed, the mass increased 4.17% (.1 g). The seventh potato was soaked in a red solution with an initial mass of 2.3 g and after the time passed, the mass increased 8.69% (.2 g).
Discussion
In nature, water diffuses from high potential to low potential environmental. High potential water has a lower concentration of solutes and vice versa. Therefore in the experiment given, the bag of water mixed with sucrose had a lower water potential than distilled water. As a result, as the molarity increased, the percent mass of the bag also increased due to the fact that water clusters around molecules of a solute. The distilled water that was placed in distilled water is known as isotonic. This means that the concentrations were equal and thus no movement occurred. On the day 2 experiment, a form of osmosis occured known as hypotonic. Essentially, when a potato slice was exposed to high water potential, it expanded and gained mass.
Conclusion
Once we finished the two labs, we noticed many things. From day one you can see that with each bag that contained more and more sucrose, the mass would increase more and more. The higher the amount of sucrose, the more increase in mass the bag would have. From day two, there weren’t many changes in the mass of the potatoes, all of the potatoes increased mass in a small amount and the only potato to decrease was the potato not in a solution at all. The potato sitting out on the paper towel must have dried out over the twenty five minutes in order for the mass to decrease.
Sources Cited
Wootton, K. (2014). AP Biology Lab - Osmosis. Retrieved from OsmosisDiffusionLab.doc