Question

Experiment 2: Diffusion Concentration Gradients and Membrane Permeability

Data Tables

Table 2: Indicator Reagent Data

Indicator	Starch Positive	Starch Negative	Glucose Positive	Glucose Negative
Glucose Test Strip	n/a	n/a	green	yellow
IKI Solution	dark blue	light brown	n/a	n/a

Table 3: Diffusion of Starch and Glucose Over Time

Indicator	Dialysis Bag After 60 Minutes	Beaker Water After 60 Minutes
Glucose Test Strip	yellow	green ( if all glucose passed to the beaker from the bag)
IKI	from incolore changed to blue dark color	pale yellow ( as iodine concentration diminishes in the beaker )

Post-Lab 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?):

EXPERIMENT 2: 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." Fol- low 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 shear. ing 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.

Answer 1

1.State your hypothesis.

That only molecules of a certain size or smaller are able to pass through a dialysis membrane. The starch molecules would be too big, but anything smaller than that, like glucose, would be able to.Also that the dialysis tubing was semi-permeable.This experiment helps illustrate the role of membranes in a cell. The membrane plays a vital part of allowing certain materials to go in and out of the cell.

2. Why is it necessary to have positive and negative controls in this experiment?

“Negative control” is expected not to have any effect .“Positive control” is known to produce the effect with the experiment that you are doing .Therefore a negative and a positive control is required to assess our test results with better accuracy.

3. Experimental set up of the procedure:

J e peruiment:- Enperimental set-up: - NIHIL Dtal (1) 7 10ome some of water 100 ml beaken Label "WATERT = Dialysis tube some submerge for 10 mine] "WATER!! 82ml water 10ome beaker Label I" DIALYSIS") - 5 ml of glucose solution 1 pipette 175ml of starch solution I different. 100ml beaker "DIALYSIS BAG SOLUTION" the solution up and min by pipetting down six times

--- ame of the dialysis bag solu "POSITIVE CONTROL glucose test strip 7 aml of the dialysis bag solution Record the final color of the glucose test strip after 1 minute positive control) 'Ifor glucose amb of thë dialysis bag Salution" 0.5 ml of IKI Record the final color of the solution I minute in Table 2. positine control I starch after for f aml of "dialysis baakes" Label E NEGATIVE CONTROL s glucose test etip aml of the "dialyes beaker" Record the final color of the glucose list strip after minute negative control) for glucose E 7>2ml of the dialysis " beaker Solution 0.5 mL of IKI Record the final color of the solution 1 minute after in Table 2 negative controut sonstarch

Soak Fold and tie at one end Tie with a rubber band ③ Use paper towels to dry for water leakage. the outside and check 8ml of "Dialysis Bag Solutions" -82ml water M" DIALYSIS" | 0 (2) Wait for 60 minutes. - 4Bucos xlsx) 17 contents "FINAL DIALYSIS BAG SOLUTION. ③ Wait for 1 min and read 4 Add 2 ml IKI and read after 1 minute ® , &me of "Dialysis beater Repeat steps ®,0 I' FINAL DIALYSIS BEAKER

_11.1:..00 __I_II - " I odine molecule I --12ije. Carbohydrete - glucose I water molecules Dialysis membrane with pores.

4.Which substance(s) crossed the dialysis membrane?

As observed in Table 3,the iodine molecules were able to pass through the dialysis membrane and into the starch solution and the glucose molecules were small enough to pass through the dialysis tubing membrane into the water.

5.Which molecules remained inside of the dialysis bag?

The starch molecules, being very large polysaccharides, were unable to pass through the membrane and hence remained inside the bag.

6.Did all of the molecules diffuse out of the bag into the beaker? Why or why not?

No, all of the molecules did not diffuse out of the bag into the beaker.Glucose and water molecules could only pass out of the bag. All the molecules of a given substance are about the same size but that molecules of different substances are different in size. Measurements show that water molecules are very small, glucose molecules are considerably larger, and starch molecules are very large.