Properties of an Artificial Membrane: Diffusion and Osmosis

Procedure: please refer to transport across semi-permeable membranes: diffusion and osmosis laboratory exercise hand out.

Observations:

Table A:

Table B:

Discussion/Analysis:

Based on the data collected and the results of the experiment, the hypothesis was correct. The iodine diffused through the tubing, but the molecules of starch/glucose solution were too large to diffuse through the tubing. Iodine, which is a fluid and has very small molecules, was able to diffuse through the dialysis tubing and reach an equilibrium on the inside and outside of the tubing. This is proven by the increase in the size of the tubing from the initial mass of 14.66 g to a final mass of 15.74 g.  However, sucrose and starch are macromolecules, so they were too large to diffuse through the tubing. This was proven by the benedicts test of the outside area, it came up negative, while the test of the tubing fluid came up slightly positive. The dialysis tubing was found not to be a good model for a cell membrane. First of all the tubing does not contain protein, which allow the passage other molecules that could not normally pass through the membrane. The process of endocytosis and exocytosis could not take place with the tubing, normally the plasma membrane would allow large molecules to go through. A possible source of error would be leaving a lot of air while tying a knot at the end of the tubing, the way to improve this for next time would be to have someone hold the tubing while the partner tied the knot. Another possible source of error would be not leaving the solutions for the amount of time required, possible way to improve this would be keeping a watch nearby at all times. Ways to improve this lab would be to add more than 5 drops of Lugol’s Iodine solution to the distilled water, therefore a more vivid observation could be recorded. Another way to improve this lab would be to extend the time of observation and then that would give time to collect clear and more accurate evidence.

Conclusion: Osmosis is the diffusion of water molecules through a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration. Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.