Diffusion Through the Cell Membrane with Osmosis 1
Diffusion Through the Cell Membrane with Osmosis Lizzie Ochs Honors Biology, Period 4 Cardinal Wuerl North Catholic High School April 30, 2018
Diffusion Through the Cell Membrane with Osmosis 2 Introduction:
There are two types of cell transport, active transport, and passive transport. For a cell to use passive transport means that the cell is moving from high to low concentration and it is moving with the concentration gradient, until it reaches equilibrium. This also means that the cell requires no ATP, or extra energy from the cell to perform its functions. Active transport requires ATP, and moves against the concentration gradient, from low to high conce ntration. (Biggs, et al., 2012) For a cell to be called selectively permeable means that it is always permeable to water meaning water can always pass through with the help of aquaporins. But, the th e cell is also semi permeable because it lets certain things in at certain times by choice. (Biggs, et al., 2012) Osmosis is the movement of water from high to low con centrations across the plasma membrane. There are three types of osmotic solutions kn ow as hypotonic, isotonic, and hypertonic environments. (Le Bach Pham, Sarah Malburg 2013). A hypotonic environment is when there is a high concentration conc entration of water outside the cell and a low concentration of pure water inside the cell. This causes the water to move into the cell. This movement of water into the cell can cause c ytolysis, the bursting of your red blood cells. (Biggs, et al., 2012) This relates to real world situations because of something called hazing, that can happen in college. One form of hazing that is quite dangerous to your body is drinking gallons of water at a time. When you drink all of this water, you are placing pla cing your cells into a hypotonic environment, causing your cells to burst. This can be extremely ex tremely harmful, and it even causes death. An isotonic environment is when the cell is in equilibrium. This Th is means there is an equal amount of solutes and water inside and outside of the cell. An example of this is our red blood cells right now that should be in an isotonic environment. (Biggs, et al., 2012) A hypertonic environment it when there is high concentration of water inside the cell and a low concentration of water outside the cell. This
Diffusion Through the Cell Membrane with Osmosis 3 causes the water to rush out of the cell. This causes the cell to shrivel. (Biggs, et al., 2012) An example of this would be when turgor pressure decreases. This happens in plant cells when they are placed into a hypertonic environment. Plants do not like this osmotic environment. Another example of this environment would be plasmolysis. This is what happens when a plant is in a hypertonic environment and it wilts. Dialysis tubing is tubing that can be opened when soaked in water. In this experiment it is used to represent a cell membrane. It will have the same functions as a cell membrane would. This means the dialysis tubing is accurate in helping to represent the movement of substances across the cell membrane. (Le Bach Pham, Sarah Malburg 2013) The major purposes of this lab are to help students understand osmosis showing a simulated p ermeable membrane using dialysis tubing, to see the effects of osmosis in an isotonic, hypertonic, and hypotonic h ypotonic environment, to then see the mass change of the simulated cells, and to see what else the dialysis tubing (simulated cell membrane) is permeable to. For the setup of the lab, there are 4 beakers that contain 200 mL of pure water, and there is one beaker that contains 200 2 00 mL of an 60% glucose solution. In set-up 1 there is a simulated cell filled with 5mL of water placed into 200mL 2 00mL of water. In set-up 2 there the re is a simulated cell filled with 5 mL of a 20% glucose solution placed into 200 mL of o f water. In set-up 3 there is a simulated cell filled with 5mL of 40% glucose placed into a beaker filled with 200 2 00 mL of water. In set-up 4 there is a simulated cell filled with 5mL of 60% glucose placed into a beaker with 200mL of water. In set-up 5 there the re is a simulated cell filled with 5mL of water placed into a beaker with 200mL of 60% glucose. And finally, in set-up 6 there is a simulated cell with 5 mL of 80% glucose solution placed into a beaker with 200mL of 60% glucose. (Diffusion Through Cell Membrane Lab Guide, 2018)
Diffusion Through the Cell Membrane with Osmosis 4 The dependent variable for part one was the mass of the simulated cell. The independent variable for part one was the amount of glucose or what type of osmotic environment the cell is placed into. The dependent variable for part two was the color change. The independent variable for part two was the placement of the starch. Some constants for part one would be the amount of solution in the simulated cell (5mL), the solution amount for each beaker (200mL), how the dialysis tubing is tied, the same dialysis tubing is used, same string is used, how the simulated cells are timed, drying the cells off before you weigh them, and how ho w you dry the simulated cells. Some constants for part two would be amount of iodine (20 drops), half a spoonful of starch, washing the simulated cell thoroughly before putting it in the solution, and the amount of water in the beaker. The control group for part one is set up one, water in water. The experimental exp erimental group for part one is the other o ther five beakers. The control group for part two is the original set up with yellow water and white starch in the simulated cell. The experimental group for pa rt two is the after, with clear water and dark purple/black pu rple/black color inside the simulated cell. (Diffusion Through Cell Membrane Lab Guide, 2018) My hypotheses for part one would be as follows. If you place the simulated cell with water in the beaker with water, then the mass of the simulated cell will stay the same because it is being placed into an isotonic iso tonic environment. If you place the simulated cell with 20% glucose into a beaker filled with water, then the mass m ass of the simulated cell will increase because the cell is being placed into a h ypotonic environment, and water will rush into the cell. This is because there is a higher concentration of water outside the cell. If you place the simulated cell with 40% glucose into a beaker filled with water, then the mass of the simulated cell will increase because the cell is once again being placed into a hypotonic environment, where water rushes into the cell. If you place the simulated cell with 60% glucose into a beaker beake r of water, then the mass of the
Diffusion Through the Cell Membrane with Osmosis 5 simulated cell will decrease because the cell is be ing put into a hypertonic h ypertonic environment, where water rushes out of the cell because there th ere is a higher concentration of water inside the cell. If you place a simulated cell with pure water into a 60% glucose solution, then the mass of the simulated cell will decrease because the water will be placed into a hypertonic environment and water will rush out of the cell. If you pla ce a simulated cell filled with 80% glucose into a solution of 60% glucose, then the mass ma ss of the simulated cell will increase because the cell is being placed into a hypotonic environment, causing water to rush into the cell. This happens because there is a higher concentration of water inside the cell and the cell is trying to reach a state of equilibrium. My hypothesis for part 2 would be , if you place a simulated cell filled with a spoonful of starch into a beaker of water and dropped in 20 drops of iodine, then the simulated cell will be permeable to the iodine and the inside of the cell will turn a blue/dark purple color. This happens because the simulated cell (cell membrane) is permeable to the iodine, but not permeable to the starch. Materials Part 1
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Dialysis tubing
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20% glucose solution
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40% glucose solution
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60% glucose solution
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80% glucose solution
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Pure water solution
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200 mL clear beaker (x5)
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Electronic balance
Diffusion Through the Cell Membrane with Osmosis 6 -
Paper towels
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Stopwatch
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String
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Pipette (x5)
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10 mL graduated cylinder
Part 2
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200 mL clear beaker
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Pure water solution
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Dialysis tubing
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String
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Paper towels
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Iodine
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Potato starch
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10mL graduated cylinder
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Plastic spoon
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Pipette (x5)
Procedure Part I: Effect of Concentration on Rate of Diffusion
1. Gather all materials. 2. Take 6 pieces of dialysis tubing that have been soaking in water. 3. Take the tubing out of the water and fold the tubing down approximately an inch, then over, then across again.
Diffusion Through the Cell Membrane with Osmosis 7 4. Tie the first end of the dialysis tubing with string in a tight knot making sure it does not come untied. Cut the excess string. 5. Repeat this folding and tying process with all 6 of the dialysis tubes. 6. Get 5 clear beakers and fill each of them with 200mL of the correct solution. Fill 4 of the beakers with water, and 2 with 60% starch solution. 7. Fill each of the 6 dialysis tubes with 5 mL of solution. Fill two with pure water, one with 20% glucose, one with 40% glucose solution, one with 60% glucose solution, and another with 80% glucose solution. 8. Now, tie the other end of each of the dialysis tubes, using the same folding and tying process as before. 9. Get 6 paper towels and label the paper towels according to the type of solution that is in each dialysis tubing. Place each dial ysis tubing on the paper towel that is labeled for it. 10. Weigh each simulated cell with an electronic balance and record the weight in grams. 11. Make sure to remember which simulated cell is filled with which solution. 12. Make sure to place each simulated cell into the proper solution at the same time. Place the simulated cells filled with water, 20% solution, 40% solution, 60% solution into separate beakers of pure water. Place the second simulated cell filled with pure water into the 60% glucose solution. Finally, place the simulated cell filled with 80% solution into the beaker with 60% glucose solution. (80% cell and pure water cell will be in same beaker). 13. Leave the simulated cells in the solutions for 3 minutes. 14. Take the cells out of the solutions and lightly dry them on a paper towel. 15. Record the weight of the simulated cell after the three minutes in the solution in grams.
Diffusion Through the Cell Membrane with Osmosis 8 16. Place the cells into their same solutions for another three minutes (3-6 minutes). 17. Repeat steps 11-12. 18. Place the cells into their same solutions for another three minutes (6-9). 19. Repeat steps 11-12. Part 2:
1. Gather all materials. 2. Get a pre-soaked dialysis tubing and tie one end using this procedure: Fold down about an inch, fold over, and then fold down again. 3. Tie the first end of the dialysis tubing with tightly with string. Tie man y knots to make sure that the simulated cell does not come untied. 4. Cut the excess string. 5. Fill the simulated cell with about a half spoon full of potato starch. 6. Add roughly 5 milliliters of pure water to the simulate cell that already has potato starch in it. 7. Shake the simulated cell to mix the water and starch. 8. Tie the other end of the dialysis tubing using the same method mentioned before. 9. Wash the simulated cell in the sink with pure water, being sure that there is no potato starch on the outside of the simulated cell. 10. Pat dry the cell using a paper towel. 11. Fill a beaker roughly half full with pure water. 12. Place the simulated cell into the beaker. 13. Place 20 drops of iodine into the beaker with the simulated cell.