Living Environment Regents Practice Test

What explains the rise of liquid in the test tube after one hour in a dialysis experiment?

1. Liquid was evaporating in the test tube

2. Water moved from the beaker into the test tube

3. The starch solution expanded the test tube

4. The dialysis membrane became permeable to starch

The correct answer is: Water moved from the beaker into the test tube

Water moving from the beaker into the test tube is the correct explanation for the rise of liquid in the test tube after one hour in a dialysis experiment. This phenomenon can be attributed to osmosis, where water molecules naturally move through a semipermeable membrane from an area of lower solute concentration (the beaker, with a higher concentration of solute) to an area of higher solute concentration (inside the test tube). In this case, the dialysis membrane allows the passage of water while retaining larger solute molecules like starch. As water enters the test tube to equalize concentration differences, the liquid level rises, demonstrating the effective principles of diffusion and osmosis in a biological context. Other possible explanations do not accurately describe the observed outcome. Liquid evaporating from the test tube would not explain the volume increase, as evaporation would lead to a decrease in liquid level. The notion that the starch solution expanded the test tube overlooks that starch cannot move through the membrane, and thus cannot be responsible for changes in liquid level within the test tube. Lastly, while the dialysis membrane's permeability is relevant, the significant movement of water is a result of osmotic pressure rather than starch crossing the membrane.