Answer to a lab question? Starch, sugar and iodine - osmosis in action.?

The bag is semi-permeable. It allowed iodine to p through it, but did not allow sugar (glucose) to enter. It's semi-permeable because not all molecules can p. If it were permeable, it wouldn't discriminate between molecules. If the bag were a cell, molecules being able to p depends on polarity and size. Macromolecules and charged particles need help to p through membranes.