Experiment 4:Cell Transport: Diffusion and Osmosis (Diffusion of Molecules through Selectively Permeable Membrane)

Aguinaldo, Co, Hermogenes, Lola, Renegado

Short Background Info

Objectives:Describe a selectively permeable membrane and explain

its role in osmosisDefine hypoosmotic, hyperosmotic, and isosmotic in terms

of relative concentrations of osmotically active substances Explain the importance of diffusion and osmosis to cells.

Short Background Info

DiffusionMovement of molecules from a higher

concentration to a lower concentration until it reaches equilibrium.

Driving force: concentration gradientSpontaneous process

Short Background Info

Diffusion

Source: Raven & Johnson Biology 9th ed.

Short Background Info

Osmosis diffusion of water across a selectively

permeable membrane due to concentration differences

Short Background Info

Osmosis

Source: Campbell Biology 10th ed.

Short Background Info

Hypotonic SolutionConcentration of solute < water

Hypertonic SolutionConcentration of solute > water

Isotonic SolutionConcentration of solute = water

Methodology

In Part A of Experiment 4, diffusion of molecules through a selectively permeable membrane was observed. The procedure requires us to prepare a dialysis bag out of collodion. But for practicality, longganisa skin was used which served as the selectively permeable membrane.

Methodology

“Membrane” set-up 

1) Filled the bag with 4 pasteur pipettefuls of 15% glucose + starch solution.

2) Tied close the bag and mixed.

3) Dropperfuls of I2KI solution + 300ml water in a 400 ml beaker

4) Placed the bag in the beaker for 30 minutes.

5) Observed physical changes.

Methodology

Basic Set Up

Methodology

To test for the presence of sugar:

1) Put into separate labelled test tubes.2 Pasteur pipettefuls of the solution from the bag +1

dropperful Benedict’s reagent

2 Pasteur pipettefuls Solution from the beaker + 1 dropperful Benedict’s reagent

2) Place test tubes in boiling water bath for 3 minutes.

3) Physical changes recorded.

Results of the Experiment

Bag Beaker

Original Contents •4 Pasteur pipettefuls of 15% glucose•4 Pasteur pipettefuls of starch solution

•300 mL water•3 dropperfuls/drops of I2KI solution

Original Color opaque golden yellow

Final Color milky white clear

Color after Benedict's test

light yellow light brown

Table 1. Results of Experiment Investigating the Permeability of Dialysis Bag to Glucose, I2KI, and Starch

Results of the Experiment

Inside Bag Inside Beaker

Results of the Experiment

After 5 minutes After 10 minutes After 15 minutes

Beaker at 20 minute mark

Discussion

Bag solution: cloudy white to bluish whiteDue to reaction of diffused ion I2 (I2KI in water) and

starchIncrease in bag solution’s volume- water and I2KI

passed through the bag

Discussion

Beaker solution: yellow to pale yellowBecause I- ions were consumed during the reaction

when diffusion occurredStarch molecules- did not diffuse out of the bag since

they are larger than the pores of the semi permeable membrane

Discussion

To test the presence of glucose:

Benedict’s TestGreenish solution – 0.5 % glucose concentrationYellow- 1%Orange- 1.5%Red- 2% or more

Discussion

Color of the solution in the bag- light yellow- 1 % glucose concentration

Color of the solution from the beaker –orange-1.5% glucose concentration

It can be concluded that both solutions contain glucose.

Discussion

Starch molecules were responsible for not allowing all the glucose molecules to pass through. It might have blocked the pores of the bag.

Conclusion

The experiment demonstrates diffusion in cells through the longanissa bag acting as the cell’s semi-permeable membrane.

Diffusion allows cells to move materials such as food, waste and other important molecules in and out without expending energy

References

Kuncaite, D. (2009) Diffusion and Osmosis Retrieved from: htttp://www.eportfolio.lagcc.cuny.edu/scholars/doc_fa09/eP_fa09/Daiva.kuncaite/documents/scb201_week3.doc.

Mader, S. (2010). Biology. New York: McGraw-Hill Companies, Inc.

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2014). Campbell Biology. USA: Pearson Education, Inc.

Starr, C., Evers, C. A., & Starr, L. (2010). Biology. USA: Brooks/Cole, Cengage Learning.