The purpose of this experiment was to see how diffusion worked within starches, glucose, and iodine. It also is to look at an example of selectively permeable walls.
A selectively permeable membrane is set up so molecules or ions can not be too big. Only molecules of a certain side are allowed to go through the membrane wall. The molecules that are supposed to go through even need help from protein carriers.
We soaked a piece of dialysis tubing in water and tied one end to make it a bag. We then filled it with a substance that was 15% glucose and 1% starch. We placed the bag into a a solution that was part iodine and part water. After a few minutes the solution inside the bag turned blue.
In the lab, the difference between the initial presence of glucose was 15%. As the iodine diffused into the dialysis tubing, the glucose and starch turned blue. This is an example of a selectively permeable membrane. The iodine goes inside the dialysis tube and the glucose comes out. The cup of iodine and the dialysis tube went through diffusion as well. When the two sections hit equilibrium the glucose presence was 5% in both.
This lab shows that diffusion and a selectively permeable membrane go hand in hand. Diffusion can happen with any type of membrane really but works best with a selectively permeable membrane. Our lab worked but didn't work as well as it could have. We put too much water in our iodine and water solution so it took almost twice as long for our tube to become fully blue.
Reece, Jane B., and Neil A. Campbell. "Membrane Structure and Function." Campbell Biology. Harlow: Pearson Education, 2011. N. pag. Print.
Purpose: The purpose of this experiment was to see what would happen when a membrane that was selectively permeable was placed in either a hypotonic, hypertonic, or isotonic. This was being tested in relation to the concentration of the substances. We wanted to see which would move through the membrane by a process called osmosis. The independent variable would be the molarities of sucrose and the dependent variable would be the mass of the bags.
Introduction: In this experiment, we were dealing with the process of osmosis. Osmosis is the diffusion of water across a selectively permeable membrane. If we think about the example of the U-shaped glass tube with a selectively permeable membrane in the center, the water will want to move to the side with the higher solute concentration. If you think of the solute and solvent as a ratio, the solvent moves to even out the ratio on the side with a lower solute concentration.
Methods: First, we needed to obtain six strips of dialysis tubing. We tied off the tubing to make a bag and filled them with 5 different molarities of sucrose and one filled with distiller water (our control group). You then closed the bag leaving enough room for osmosis to occur. After the bags were filled, we took the mass of each. We then took the bags back to our table, put them in cups labeled with which solution it was. We filled the cups with water and let them sit for about 30 minutes. After 30 minutes had passed, we removed the bags from the cups, and weighed them once again.
Graphs and charts:
Discussion: By looking at the data of this lab alone, I am not sure I would understand the relationship between Molarity and mass. The trend we should be seeing is as the Molarity gets larger, so should the percent change of the mass. As the Molarity increases, it takes more water to try and balance out the solution inside and out a state that we call equilibrium. The water naturally wants to balance out the concentration across the membrane. I don't think that our data necessarily showed that. Just by observing the lines that the plotted data makes (both class average and lab group) it zig-zags. In a perfect world, the lines would just gradually slant upwards. This discrepancy in data could be due to the dialysis bags not being filled with the same amount of liquid. It could possibly be due to amount of liquid in the cup, or an error in the weighing process. The results of the lab were what I expected them to be because I knew that since Bag F had the highest concentration of sucrose, it would take the most water to balance. Our data wasn't what I expected because I thought that like I said the lines would just go up not up and down.
Conclusion: Overall, I think that our data was helpful to see a trend I was already aware of. Had I not known what I was looking for our data would not have lead me in the right direction. Our lab data shows however, that the membrane was selectively permeable and that therefore the mass will increase.
References: Reece, Jane B. Campbell Biology. San Francisco: Pearson Benjamin Cummings, 2011. Print.
Lab One Diffusion and Osmosis. College Board
Purpose: The purpose of this experiment is to analyze the water potential of potato cells, and it's correlation to the molarity of sucrose solutions. The independent variable was the various molarities of the sucrose solutions and the dependent variable was the final mass of the potato cylinders. They were soaked in water as well as a control.
Introduction: Molecules in cells are constantly moving and bumping into each other. They have a tendency to move from areas of higher concentration to areas of lower concentration in a process called diffusion. Osmosis is the diffusion of water molecules through a selectively permeable membrane (one that only allows certain substances to diffuse across it.) Waters tendency to leave one area for another is measured by water potential (which is 0 in pure water.) 2 factors most influence water potential. The first is solute potential, which is the effect that the solute potential has on the solution's water potential. Water movement is also directly proportional to the pressure potential of a system, which limits the expansion of cells by exerting pressure back into the cell if it fills too much. Diffusion and osmosis are crucial in maintaining balance in the concentrations of various substances inside and out of the cell membrane.
Methods: We cut cores out of a potato and soaked them in sucrose solutions of various concentrations. We weighed them before and after soaking, and then calculated the mass difference and it's relationship to the sucrose concentration.
Graphs and Charts:
Discussion: The most noticeable trend in our data is that the potatoes gained mass when soaked in water and 0.2M sucrose, but began to lose mass once the cores were placed in a sucrose solution of 0.4M and up. This most likely is because potatoes contain sucrose, and its concentration in potatoes is between 0.2 and 0.4M. When soaked in solutions of 0.0 and 0.2M, sucrose rushed out of the potato and into the water, while water rushed into the cores. This is why the potato cores gained mass when soaked in solutions of lower concentrations. However, when the potatoes were soaked in solutions with a higher concentration, water rushed out and they lost mass. The trend of continually lowering mass continued until our final test, 1.0 M sucrose. This could very well be an error in our experimentation, but since the other groups in the class had similar result I think it was the pressure potential of the potato cores limiting their water intake.
Conclusion: The potato cores gained mass in solutions of 0.2M and less and lost mass in solutions of 0.4M and more. This leads to the conclusion that the sucrose concentration of potatoes is around 0.3M. It stopped losing mass at 1.0M sucrose however, possibly due to error in experimentation or possibly the potato exerting pressure on tats interior to stay the same size.
Campbell Biology Ninth Edution
The purpose of this lab was to see how water and salt can affect the onion. It also shows how plasmolysis shrinks the cytoplasm. The independent variable is the salt concentration and the dependent variable is the tonicity of the onion.
Introduction: Cells have a tendency to move and bump into each other constantly. Diffusion is the result of this contact. Diffusion is the random movement of molecules to an area of lower concentration from an area of higher concentration. Osmosis is a variation of diffusion. This is the diffusion of water molecules through a selectively permeable membrane from a region of higher concentration to a region of lower concentration. Water potential is the measure of free energy of water in a solution. Dialysis is the movement of a solute through a selectively permeable membrane. When plant cells are placed in a hypertonic solution they lose water in a process called plasmolysis. Conversely, when placed In a hypotonic solution hey take in water and become turgid, and in an isotonic solution water flows in and out at an even rate and the cell becomes flaccid. This experiment takes place to measure the osmosis of water in and out of an onion cell.
Methods: First, you are to obtain the epidermis of an onion. After doing so prepare a wet mount and observe the onion under 100x magnification. Record what you see, and then add a couple drops of 15% salt solution. Draw the solution across the onion using a paper towel. Observe and then record the difference. Once that is done, flood the onion epidermis with water and describe what happens.
Graphs/Charts/Data: First photo is the onion cell when it is turgid and the second photo is the onion cells flaccid or plasmolyzed.
Discussion: Part E of the lab centers around plasmolysis. Plasmolysis is, "a phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment". In the case of onions, the plasma membrane is pulling away from the cell because of the 15% salt solution. In a normal hypertonic solution, onion cells would still have its plasma membrane pull away, but the salt helps draw the water out of the cell, which we can see by the change of color in the pictures. When the onion is flooded with fresh water again, it returns to its normal color and shape. We are placing the cell back into a hypotonic solution and the cell is turgid again.
Conclusion: Looking at the data, the onion seems to become more plasmolyzed. The more salt outside the cell, the more water has to rush out of the onion to balance the concentrations. The onion cells become turgid as salt is decreased and plasmolyzed as salt is added.
References: Campbell Biology Ninth Edition
Lab One: Diffusion and Osmosis College Board