Your lab group is experimenting with the diffusion of molecules across a membrane. Dialysis tubing is used as a model cell membrane because is it semi-permeable, allowing small molecules to cross the membrane, but NOT larger molecules, like starch. A starch solution is placed in the dialysis tubing and then the dialysis tubing is placed in an iodine and water solution. Iodine is used as an indicator for the presence of starch. Normally, iodine is a yellow-brown color (on the left), but in the presence of starch, it turns a deep purple (right). After observing the experimental setup for 20 minutes, the iodine solution remains brown, but the starch solution inside the dialysis tubing is purple and swollen. What CANNOT be concluded from the results?

A] Iodine is a small molecule and diffused through the dialysis tubing INTO the starch solution.
B) Starch is a large molecule and could NOT diffuse through the dialysis tubing into the iodine solution.
C) Starch requires ATP energy for transport and therefore cannot cross the dialysis tubing into the iodine solution.
D) The starch solution is hypertonic to the iodine solution, causing water to move across the dialysis tubing INTO the starch solution.

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  1. it was C

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