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Name: Pradish Menon
Class: F4 Mozart
Date: 22/3/06
Experiment 3.1: The movement of Substance across the Plasma Membrane
Problem Statement
:What factor influences the diffusion of substances across a semi permeable membrane?
Objective
: To To st study th the fa factors in influencing th the di diffusion of of su substances ac across a semi-permeable membrane.
Hypo Hypotthesis
: The diffusion of mole olecules through a semi emi-pe -permeab eable membrane is based on the size of the molecules.
Manipulated Variable : Types of solutes in the Visking Tubing. Responding Responding Variab Variable le : Presence Presence of glucose. glucose. Fixed Variable : Duration of the experiment. Materials & Apparatus: Benedict’s solution, 1% starch suspension, iodine solution, 30% glucose solution, a Visking tubing and cotton thread, test tubes, beakers and a Bunsen burner. Techn Techniq ique ue Use Used d
:Dif :Diffe fere rent nt size sized d mol molec ecul ules es are are used used to test test the the per perme meab abil ilit ity y of the the Visking tubing which has a semi-permeable membrane.
Diagram
:
Name: Pradish Menon
Class: F4 Mozart
Date: 22/3/06
Procedure: 1. The Visking tubing was soaked in water for 5 minutes to soften it. 2. The Visking tubing was then opened. One end of the Visking tubing was tied with a piece of cotton thread to prevent leakage. 3. The Visking tubing was filled with 15 ml of glucose solution and 15ml of starch solution. 4. The other end of the Visking tubing was tied with another piece of thread. The colour of the solution was recorded. 5. The outer surface of the Visking tubing was rinsed with running water from a tap. 6. 400ml of water and 15ml of iodine solution was mixed in a beaker. The colour of the solution was recorded. 7. The Visking tubing was placed in the beaker (figure 3.7) and was left to stand for 40 minutes. 8. After 40 minutes, the Visking tube was taken out and placed in a dry beaker. 9. The colour of the solutions in the Visking tubing and the beaker was observed and recorded. 10. Both the solutions were tested for the presence of glucose using Benedict’s solution. 11. 2 ml of each solution was poured into separate test tubes and 1ml of Benedict’s solution was added to each test tube. The solution was heated in a water bath for about 5 minutes and the change in colour was recorded.
Discussion: 1)
State all the variables in the experiment. Manipulated: Type of solute in the Visking tube. Responding: Final colour of the solution in the Visking tube. Constant: Surrounding temperature.
2)
Based on the results, make an inference regarding the size of the iodine molecules as compared to the size of the starch molecules. The size of iodine molecules are smaller than the size of starch molecules. Iodine molecules can diffuse through the walls of the Visking tubing turning the solution blue-black.
3)
What inference can you make regarding the size of the starch molecules when compared to the size of the pores on the Visking tubing? Starch molecules are too large to diffuse out through the pores of the Visking tubing. Therefore, the colour of the solution in the beaker does not change at the end of the experiment.
Name: Pradish Menon
Class: F4 Mozart
Date: 22/3/06
4)
What do the results of the Benedict’s test show? What inference can you make from the results? The brick red precipitate is a result of the Benedict’s test. Glucose molecules can easily diffuse through the membrane of the Visking tubing as the glucose molecules are small. Therefore, this shows that glucose molecules are present in the beaker.
5)
Predict the outcome of the results if the experiment is repeated by filling the Visking tubing with glucose solution and the beaker with starch suspension? If the experiment is repeated by filling the Visking tubing with glucose solution and the beaker with starch suspension, the solution will turn blue-black.
6)
Based on the experiment, what analogy can you make between the Visking tubing and the digestive and the digestive system? In the human digestive system, large molecules are hydrolysed in a simple sugar, which can be absorbed easily through the semi-permeable plasma membrane of the epithelial cells lining the intestinal wall.
Results: Contents Visking Tubing
Beaker
Conclusion
Initial Final Colour Colour Colourless Blue-black
15ml of glucose solution+15ml of starch suspension 400ml of distilled water Yellow + 15ml of iodine solution
Yellow
Benedict’s Test Brick-red precipitate. Positive. Brick-red precipitate. Positive
:The diffusion of molecules across a semi-permeable membrane is based on the size of the molecules. Hypotesis is accepted.
