Just Passing Through

Cell membranes are semipermeable, meaning that only certain substances, based on the molecule’s size and electric charge, can pass through. Molecules passively move from areas of high concentration to areas of low concentration. Starch, which is a large molecule that cannot pass through most membranes, can be identified with indicator solutions, such as Lugol Solution—an amber-colored indicator solution that turns black in the presence of starch. In this activity, you will observe diffusion of iodine molecules through a semipermeable membrane that allows for passage of molecules up to 180kDa.

This activity supports 3-dimensional learning and builds toward the following:

• NGSS Scientific and Engineering Practice: Constructing Explanations
• NGSS Core Idea: From Molecules to Organisms: Structures and Processes