Final answer:
No net water movement should occur when a bag with 25% sucrose is placed in a 25% sucrose solution, as they are isotonic to each other. The experiment with lactose and fructose indicates selective permeability, as only fructose was able to diffuse out of the dialysis bag.
Step-by-step explanation:
When you placed the bag containing 25% sucrose in a beaker of 25% sucrose, there should not have been a net flow of water in any particular direction because the solutions inside the bag and in the beaker are isotonic to each other. No net movement of water occurs because the concentration of solute (and thus the water potential) is the same on both sides of the membrane.
In the experiment described, where the dialysis-tubing bag contained 5% lactose and 5% fructose and was placed in distilled water, fructose was detected in the distilled water outside the bag after four hours but lactose was not. This suggests that fructose molecules are small enough to pass through the pores of the dialysis tubing, while lactose molecules are too large. This demonstrates selective permeability of the dialysis-tubing membrane, allowing only certain molecules to pass through based on size.