Using dialysis tubing to model diffusion of a cell membrane and investigating the influence of solute concentration on osmosis
Purpose
* Discover how dialysis tubing diffuses the cell membrane * Explore the effect of solute concentration on osmosis
Background
A cell membrane is a very significant function in the human body. In one sense, it is used as a barrier to keep the enzymes, DNA, and metabolic pathways that bundles everything together. Cell membranes are also used as a gateway for waste projects that must be discharged and essential materials (oxygen, water, etc.) must enter through it. When a membrane is called semipermeable, it means that it will allow certain molecules or ions to pass through it by diffusion and occasionally specialized facilitated diffusion. When the cell membrane expends energy, it is known as active transport, or when the process is driven by kinetic energy, it is passive transport.
Hypotheses
Activity A: Diffusion
-If glucose can pass through the semi-permeable membrane, then the solution inside the dialysis tubing will test positive for glucose after 48 hours. -If starch can pass through the semi-permeable membrane, then the solution outside the dialysis tubing will turn black. -If iodine (IKI) can pass through the semi-permeable membrane, then the solution in the cup will turn black.
Activity B: Osmosis
-If sucrose molarity influences osmosis then % change in mass will increase as molarity increases.
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Materials
* Dialysis tubing
* Plastic cup
* Glucose/starch solution
* Distilled water
* Iodine-potassium iodide (IKI) solution
* Dropping pipet
* Glucose test strips
* Funnel
Procedure A
1. Pour 160-170 mL of distilled water into a plastic cup. Add about 4 mL of IKI solution to the water and mix well. Record the initial solution color in Table 1. Dip a glucose test strip into the solution and record the initial glucose test results in Table 1. Use the + symbol to indicate a positive test result for glucose and the symbol to indicate a negative result. Discard the used test strip.
2. Dip a fresh glucose test strip into the glucose/starch solution. Record the initial results in Table 1. Discard the used glucose test strip.
3. Obtain a piece of dialysis tubing that has been soaked in water. The tubing should be soft and pliable. Roll the tubing between your thumb and index finger to open it. Close one end of the tube by knotting it or tying it off with spring. This will form a bag.
4. Using a small funnel, pour 15 mL of glucose/starch solution in the dialysis bag. Smooth out the top of the bag, running it between your thumb and index finger to expel the air. Tie off the open end of the bag. Leave enough room in the bag to allow for expansion. Record the initial color of the glucose/starch solution in Table 1.
5. Immerse the dialysis bag in the solution in the cup. Make sure that the portion of the bag that contains the glucose/starch solution is completely covered by the solution in the cup at all times.
6. Wait 30 minutes before continuing.
Procedure B
1. Pour 160-170 mL of distilled water into a plastic cup. Label with the concentration of sucrose you will test 2. Obtain a piece of dialysis that has soaked in water. Roll the soft and pliable tubing between thumb and index finger to open. Close off one end of tube with string to form a bag. 3. Use a small funnel to four 15 mL of sucrose solution into dialysis bag. Run between thumb and index finger to expel the air. Tie off the open end of bag but leave enough room in the bag to allow expansion. 4. Dry the bag on paper town and determine mass. Record this as the initial mass in Table 2. 5. Immerse the dialysis bag into the water in the cup. Make sure the sucrose portion is completely covered in water the whole time. Wait 30 min before continuing 6. After 30 minutes, remove the bag from cup and dry with paper towels. Mass the bag and record final mass in Table 2. Finally, determine the change in the mass of the bag and record this data.
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Results
Activity A: To track diffusion among various molecules, studies were conducted during the initial set-up and 24 hours after the preliminary process was finished. On the first day, the solution inside the dialysis tubing was clear and when tested for glucose, resulted as positive. On day two, the solution outside the dialysis tubing was still amber in color. Nonetheless, the solution outside the dialysis tubing confirmed positive for glucose after 24 hours. By the third day, the solution inside the dialysis tubing was black in color after the 24 hour period and still tested positive for the presence of glucose. Activity B: In activity B, all of the dialysis bags gained mass, except for the bag which contained the 0.0 M solution. The bag with a 0.2 M solution had a percent mass gain of 6%. The 0.4 M solution resulted in a percent gain of 15%, the 0.6 M solution lead to an increase of 34% and the 0.8 M solution resulted in a mass expansion of 56%.
Conclusion:
The trends in the data support the hypotheses that the sucrose molarity influences osmosis and that the percentages change in mass as molarity increases with the action of diffusion. The hypotheses also proved correct in the case of starch passing through the semi-permeable membrane, and turning the solution outside the dialysis tubing black, as well as the glucose and the IKI testing positive after 48 hours of submergence. However, the IKI solution resulted in an amber color instead of black outside of the dialysis tubing, a fault which may indicate mechanical error, and must be accounted for in future experiments. The accuracy of the results could be improved with better consistency among dialysis tubing.
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The Effect of Concentrations of Starch and Sugar Solutions on Synthetic Semi-Permeable Membranes By: Jamie Hardy Question: Is dialysis tubing selectively permeable? Hypothesis: If one has dialysis tubing, which is dipped in water, filled with Gatorade and starch and is left for 15 minutes, the sugar in the Gatorade will exit the dialysis and into the water. So the dialysis is semi-permeable. ...
Every bag was secured inversely, leaving a large amount of room for error. Similarly, the quantities of solutions poured were very similar, but measurements were not exact. In the future, the experiment would need to be generated with precise measuring techniques and more isolation among groups to generate better results. The use of dialysis tubing in this experiment compels the experimenter to question whether a membrane would behave in the exact same manner as the tube in this setting, or whether the presence of different material changes the reaction in any way. Experimentation with a real cell membrane would be necessary to determine this.
