**answer all question thoroughly for good rating**

Experiment 2 Diffusion - Concentration Gradients andMembrane Permeability Experiment Inventory

Materials 10 mL 1% Glucose Solution, C6H12O6 4mL 1% Iodine-Potassium Iodide (IKI) 5 mL Liquid Starch, C6H10O5 4Glucose Test Strips 4 Small Rubber Bands (Latex Warning: Handlewith gloves on if allergic.) *Permanent Marker *Water *Scissors*Paper Towels *Stopwatch/Timer

Labware (5) 100 mL Beakers 6 Pipettes Ruler 100mL Graduated Cylinder **15.0 cm Dialysis Tubing

**Be sure to measure and cut only the length you need for thisexperiment. Reserve the remainder for later experiments.

lab

EXPERIMENT DIFFUSION – CONCENTRATION GRADIENTS AND MEMBRANEPERMEABILITY **In this experiment, you willdialyze a solution of glucose and starch to observe the effect of aselectively permeable membrane on the diffusion of these molecules.To assess the movement of these molecules, you will use indicators.An indicator is a substance that changes color when in the presenceof the substance it indicates. You will be using an indicator totest for the presence of starch and glucose. Attention! •Do not allow the open end of the dialysis tubing to fall into thebeaker. If it does, remove the tube and rinse thoroughly with waterbefore refilling it with the starch/glucose solution and replacingthe tubing to the beaker. • Dialysis tubing must be soaked in waterbefore you will be able to open it up to create the dialysis “bag.”Follow these directions for this experiment:

1. Soak the tubing in a beaker of water for 10 minutes.2. Place the dialysis tubing between your thumb and forefinger, andrub the two digits together in a shearing manner. This motionshould open up the “tube” so that you can fill it with thedifferent solutions. • If you make a mistake, the dialysis tubingcan be rinsed and used again. • You may need to reuse beakersthroughout this experiment. When this is the case, clean beakersbetween uses.

PROCEDURE 1. Measure and pour 50 mL of waterinto a 100 mL beaker using the 100 mL graduated cylinder.2. Label this beaker “water.” Cut a piece ofdialysis tubing 15 cm long. Submerge the dialysis tubing in thewater for at least 10 minutes. 3. Measure and pour82 mL of water into a second 100 mL beaker using the 100 mLgraduated cylinder. Label this beaker “dialysis.” This is thebeaker you will put the filled dialysis bag into in Step 10.4. Make the glucose/starch mixture. Use agraduated pipette to add 5 mL of glucose solution to a third 100 mLbeaker and label it “dialysis bag solution.” Use a differentgraduated pipette to add 5 mL of starch solution to the samebeaker. Mix by pipetting the solution up and down six times.5. Using the same pipette that you used to mix thedialysis bag solution, remove 2 mL of the dialysis bag solution andplace it in a clean beaker. Label this beaker “positive control.”This sample will serve as your positive control for glucose andstarch. a. Dip one of the glucose test strips into the 2 mL ofglucose/starch solution in the fourth beaker. After 1 minute haspassed, record the final color of the glucose test strip in Table2. This is your positive control for glucose. b. Use a pipette totransfer approximately 0.5 mL of IKI into the 2 mL ofglucose/starch solution in the fourth beaker. After 1 minute haspassed, record the final color of the glucose/starch solution inthe beaker in Table 2. This is your positive control for starch.6. Using a clean pipette, remove 2 mL of waterfrom the “dialysis” beaker and place it in a clean beaker. Labelthis beaker “negative control.” This sample will serve as yournegative controls for glucose and starch. a. Dip one of the glucosetest strips into the 2 mL of water in the beaker. After 1 minutehas passed, record the final color of the glucose test strip inTable 2. This is your negative control for glucose. b. Use apipette to transfer approximately 0.5 mL of IKI into the 2 mL inthe beaker. After 1 minute has passed, record the final color ofthe water in the beaker in Table 2. This is your negative controlfor starch. Note: The color results of these controls determine theindicator reagent key. You must use these results to interpret therest of your results. 7. After at least 10 minuteshave passed, remove the dialysis tube, and close one end by foldingover 3.0 cm of one end (bottom). Fold it again, and secure with arubber band (use two rubber bands if necessary).8. Test to make sure the closed end of thedialysis tube will not allow the solution to leak out. Dry off theoutside of the dialysis tube bag the paper towels. To open thedialysis tubing, use your thumb and pointer finger to rub thetubing between your fingers. Then, add a small amount of water tothe bag and examine the rubber band seal for the leakage. Note: Besure to remove the water from the inside of the bag beforecontinuing. 9. Using the same pipette that wasused to mix the glucose-starch solution in Step 4, transfer 8 mL ofthe dialysis bag solution beaker to the prepared dialysis bag.10. Place the filled dialysis bag in the“Dialysis” beaker, leaving the open end draped over the edge of thebeaker as shown in Figure 7. 11. Allow thesolution to sit for 60 minutes. Clean and dry all materials exceptthe beaker holding the dialysis bag. 12.After thesolution has diffused for 60 minutes, remove the dialysis bag fromthe beaker, and empty the contents of the bag into a clean, drybeaker. Label the beaker “final dialysis bag solution.”13. Test the final dialysis bag solution for thepresence of glucose by dipping one glucose test strip into thedialysis bag. Wait 1 minute before reading the results of the teststrip. Record your results for the presence of glucose in Table 3.Figure 7: Step 10 reference. 14.Test for thepresence of starch by adding 2 mL IKI. After 1 minute has passed,record the final color in Table 3. 15. Use apipette to transfer 8 mL of the water in the beaker to a cleanbeaker. Label this beaker “final dialysis beaker solution.” Testthe beaker water for the presence of glucose by dipping one glucosetest strip into the beaker. Wait 1 minute before reading theresults of the test strip, and record the results in Table 3.16.Test for the presence of starch by adding 2 mLof IKI to the beaker water. Record the final color of the beakersolution in Table 3.

Diffusion Concentration Gradients and Membrane Permeability

Data Tables

Table: Indicator Reagent Data

Indicator	Starch Positive	Starch Negative	Glucose Positive	Glucose Negative
Glucose Test Strip	n/a	n/a
IKI Solution			n/a	n/a

Table: Diffusion of Starch and Glucose OverTime

Indicator	Dialysis Bag After 60 Minutes	Beaker Water After 60 Minutes
Glucose Test Strip
IKI

Questions

1. State your hypothesis.
2. Why is it necessary to have positive and negative controls inthis experiment?
3. Draw a diagram of the experimental set-up. Use arrows to depictthe movement of each substance in the dialysis bag and thebeaker.
4. Which substance(s) crossed the dialysis membrane? Support yourresponse with data-based evidence.
5. Which molecules remained inside of the dialysis bag?
6. Did all of the molecules diffuse out of the bag into thebeaker? Why or why not?

Reflection (Discuss what you have learned bydoing this experiment. How have your ideas changed? Do you have anynew questions? What connections did you make between the lab andlecture?):