Question

**answer all question thoroughly for good rating**

Experiment 2 Diffusion - Concentration Gradients and Membrane Permeability Experiment Inventory

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

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

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

lab

EXPERIMENT DIFFUSION – CONCENTRATION GRADIENTS AND MEMBRANE PERMEABILITY **In this experiment, you will dialyze a solution of glucose and starch to observe the effect of a selectively 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 presence of the substance it indicates. You will be using an indicator to test for the presence of starch and glucose. Attention! • Do not allow the open end of the dialysis tubing to fall into the beaker. If it does, remove the tube and rinse thoroughly with water before refilling it with the starch/glucose solution and replacing the tubing to the beaker. • Dialysis tubing must be soaked in water before 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, and rub the two digits together in a shearing manner. This motion should open up the “tube” so that you can fill it with the different solutions. • If you make a mistake, the dialysis tubing can be rinsed and used again. • You may need to reuse beakers throughout this experiment. When this is the case, clean beakers between uses.

PROCEDURE 1. Measure and pour 50 mL of water into a 100 mL beaker using the 100 mL graduated cylinder. 2. Label this beaker “water.” Cut a piece of dialysis tubing 15 cm long. Submerge the dialysis tubing in the water for at least 10 minutes. 3. Measure and pour 82 mL of water into a second 100 mL beaker using the 100 mL graduated cylinder. Label this beaker “dialysis.” This is the beaker you will put the filled dialysis bag into in Step 10. 4. Make the glucose/starch mixture. Use a graduated pipette to add 5 mL of glucose solution to a third 100 mL beaker and label it “dialysis bag solution.” Use a different graduated pipette to add 5 mL of starch solution to the same beaker. Mix by pipetting the solution up and down six times. 5. Using the same pipette that you used to mix the dialysis bag solution, remove 2 mL of the dialysis bag solution and place it in a clean beaker. Label this beaker “positive control.” This sample will serve as your positive control for glucose and starch. a. Dip one of the glucose test strips into the 2 mL of glucose/starch solution in the fourth beaker. After 1 minute has passed, record the final color of the glucose test strip in Table 2. This is your positive control for glucose. b. Use a pipette to transfer approximately 0.5 mL of IKI into the 2 mL of glucose/starch solution in the fourth beaker. After 1 minute has passed, record the final color of the glucose/starch solution in the beaker in Table 2. This is your positive control for starch. 6. Using a clean pipette, remove 2 mL of water from the “dialysis” beaker and place it in a clean beaker. Label this beaker “negative control.” This sample will serve as your negative controls for glucose and starch. a. Dip one of the glucose test strips into the 2 mL of water in the beaker. After 1 minute has passed, record the final color of the glucose test strip in Table 2. This is your negative control for glucose. b. Use a pipette to transfer approximately 0.5 mL of IKI into the 2 mL in the beaker. After 1 minute has passed, record the final color of the water in the beaker in Table 2. This is your negative control for starch. Note: The color results of these controls determine the indicator reagent key. You must use these results to interpret the rest of your results. 7. After at least 10 minutes have passed, remove the dialysis tube, and close one end by folding over 3.0 cm of one end (bottom). Fold it again, and secure with a rubber band (use two rubber bands if necessary). 8. Test to make sure the closed end of the dialysis tube will not allow the solution to leak out. Dry off the outside of the dialysis tube bag the paper towels. To open the dialysis tubing, use your thumb and pointer finger to rub the tubing between your fingers. Then, add a small amount of water to the bag and examine the rubber band seal for the leakage. Note: Be sure to remove the water from the inside of the bag before continuing. 9. Using the same pipette that was used to mix the glucose-starch solution in Step 4, transfer 8 mL of the 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 the beaker as shown in Figure 7. 11. Allow the solution to sit for 60 minutes. Clean and dry all materials except the beaker holding the dialysis bag. 12.After the solution has diffused for 60 minutes, remove the dialysis bag from the beaker, and empty the contents of the bag into a clean, dry beaker. Label the beaker “final dialysis bag solution.” 13. Test the final dialysis bag solution for the presence of glucose by dipping one glucose test strip into the dialysis bag. Wait 1 minute before reading the results of the test strip. Record your results for the presence of glucose in Table 3. Figure 7: Step 10 reference. 14.Test for the presence of starch by adding 2 mL IKI. After 1 minute has passed, record the final color in Table 3. 15. Use a pipette to transfer 8 mL of the water in the beaker to a clean beaker. Label this beaker “final dialysis beaker solution.” Test the beaker water for the presence of glucose by dipping one glucose test strip into the beaker. Wait 1 minute before reading the results of the test strip, and record the results in Table 3. 16.Test for the presence of starch by adding 2 mL of IKI to the beaker water. Record the final color of the beaker solution 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 Over Time

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 in this experiment?
3. Draw a diagram of the experimental set-up. Use arrows to depict the movement of each substance in the dialysis bag and the beaker.
4. Which substance(s) crossed the dialysis membrane? Support your response 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 the beaker? Why or why not?

Reflection (Discuss what you have learned by doing this experiment. How have your ideas changed? Do you have any new questions? What connections did you make between the lab and lecture?):

Answer 1

1. The positive and negative controls indicate the presence or absence of starch. whem potassium iodide solution added the starch solution will turn blue in colour which is positive control for the starch and empty water added with potassium iodided does not give any blue colour is the negative control for the starch. Inorder to differentiate the starch,sucrose solution from the water KI is added. Decrease in the blue Colour intensity because of the diffusion of water into the dialysis bag indicates the osmosis. Glucose strip indicates the presence or absence of glucose in the solution inorder to determine the diffusion of water.

2. Only water molecules will enter the dialysis bag from  the beaker to maintain the equal concentration on either side. Dialysis bag acts as semipermiable membrane and allow only water molecules to enter inside the bag. As the starch does not dissolve it can not increase the concentration but sucrose. so water diffuses across the membrane into the bag.

3. no molecules diffuse out of the bag into the beaker because the concentration in the bag is high in comparision with the beaker

4.