LabBench Activity

Closer Look: Concentration Gradient

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Notice that the starch molecules are too large to pass through the pores in the membrane. The iodine molecules move across the membrane in both directions, but their net movement is from the bag, where their concentration is higher, into the beaker, where their concentration is lower. The iodine combines with starch to form a purplish-colored compound.

The net movement of water is into the beaker.