Lab 9: Diffusion Through A Membrane Part 1

Summary

In this lab students experimented with the diffusion of certain molecules through an artificial cell membrane. The artificial cell membrane was made of a very thin tubing with small pores that allowed very small molecules to pass through. The tube was filled with starch and glucose then closed. This tubing was then placed in a beaker of water for an hour. Also during this time 10 drops of starch indicator ( Iodine) was added to the liquid surrounding the tubing, creating an amber color. So to recap:

Inside the Cell

-Starch
-Glucose

Outside the Cell

-starch indicator

Figure 1. Initial State of Experiment

While we waited I explained indicators. Indicators tell us if a specific molecule is in the liquid by changing the color of the liquid. For example the starch indicator indicates if there are starch molecules in a liquid by changing from amber to black when in the presence of starch. A glucose indicator normally changes from its normal blue color to a red color when in the presence of glucose. 

Figure 2. Indicators mixed with water, starch, or glucose

After one hour the tubing had become black. This is because the starch indicator had diffused to an overall lower concentration by moving into our artificial cell. Inside the cell it mixed with the starch to create a black color. We then tested the water outside of the tubing with a glucose indicator. The liquid turned red, indicating that glucose did escape from the cell. But did starch?

Figure 3. Final State of Experiment