Final answer:
The student was demonstrating selective permeability of the cell membrane through an experiment where iodine caused a color change, indicating its ability to pass through the membrane and react with starch.
Step-by-step explanation:
The student was demonstrating the function of selective permeability of the cell membrane. When iodine, which can penetrate the membrane, was added to the water, it diffused through the bag and interacted with the starch inside the bag, turning the solution purple. This activity showcases how the cell membrane allows certain substances to pass while blocking others, maintaining a state of homeostasis within the cell.
Passive transport is a process by which substances move across cell membranes without the input of energy. The phospholipid bilayer of the cell membrane is organized in a way that makes the membrane selectively permeable – a characteristic crucial for the proper functioning of cells in maintaining a balanced internal environment.