4. Pass out the Cell Membrane Bubble Lab document. Give students 1-2 minutes to read through the directions. Then go over the major points: Students will be using bubble solution, trays, and straws to create simulated cell membranes. Point out where students can find the materials in the classroom. A soap bubble (see Figure 7 a) has two spherical surfaces (inside and outside) with a thin layer of liquid in-between. Like a balloon, the pressure inside a soap bubble is greater than that on the outside. As we will see shortly, this difference in pressure depends on the surface tension γ of the liquid and the radius R of the bubble.
In each diagram below, a “cell” with a semipermeable membrane has been placed in a beaker containing substances that are dissolved in water. The membrane is permeable to water & iodine. It is not permeable to glucose, sodium (Na+), or starch. Please remember that iodine (Lugol’s solution) is an indicator for starch! Therefore, it will turn