Diffusion Lab Report

The diffusion lab created an understanding of the processes inside a cell using iodine, cornstarch and water. The purpose of the lab was to observe the diffusion of a substance across a semi permeable membrane.  To do this, iodine was used as the indicator and a plastic baggie was used as the permeable membrane that separated it from the substance it indicated which in this case was starch. Since iodine is an indicator for starch, the predicted outcome was that when osmosis, a specified form of diffusion with water, occurred and the iodine moved across the membrane, it would change color in the presence of starch.  Initially, the iodine was hypertonic since it was highly concentrated in the beaker. As it moves across the permeable membrane, it would be diluted to a lower concentration by the water and became hypotonic. It was predicted that the iodine would diffuse across the permeable membrane so that the concentration of iodine in both the baggie and the beaker would be the same and thus isotonic.

After 15 minutes of observation, the solution in the baggie changed from white to a shade of purple while the solution in the beaker remained orange. This leads to the conclusion that the iodine diffused through the baggie and underwent the process of osmosis, as predicted, to indicate the starch by changing its color. Since the contents of the beaker remained unchanged, it was apparent that the semi permeable membrane did not allow the starch to transfer from the baggie to the beaker thus the baggie was selectively permeable. The occurrences in this lab mimic the behavior of the cell membrane. The cell membrane is what protects the cell and selectively controls the movement of molecules into and out of the cell. Thus, it is selectively permeable just as the baggie was selective with the iodine and the starch.  This is how cell membranes react with water and food molecules. Certain molecules can pass through the cell membrane to benefit the cell whereas harmful molecules are blocked from entering the cell. This process is required for the cell to function.

Looking outside of this experiment, diffusion is utilized on a daily basis by most people. For example, when a tea bag is placed in boiling water, the molecules of the tea leaves diffuse through the tea bag to color and flavor the water. Another situation where molecules are diffused by osmosis is sugar and coffee. When sugar is dissolved in coffee, the sugar molecules spread throughout the coffee and sweeten its taste. Not all diffusion is beneficial. In the case of cigarette smoke, it diffuses into the air and causes second hand smoke inhalation. Also, car and truck emissions of carbon monoxide can be deadly when diffused in high concentrations. That is why the automobile engines cannot be started inside a closed area such as a garage. These examples show how diffusion has both a positive and negative effect on the human population.