Which of the following statements about the conditions shown in the U-shaped tube are true?

Question

A U-shaped tube with two arms A and B that are separated by a membrane at the base of the U. Arm A contains solution with lower concentration of sugar, arm B contains solution with higher concentration of sugar. Water passes through membrane from arm A to arm B. Fluid levels on either side of the membrane are equal.
Select all that apply.

Solutes can pass through the selectively permeable membrane from right to left, but free water cannot.
Water is tightly clustered around the hydrophilic solute molecules on both sides of the membrane.
There is more solute in the left arm of the tube than in the right arm of the tube.
There is less free water in the right arm of the tube than in the left arm of the tube.

Answer 1

Let's evaluate each statement in the context of the scenario provided with the U-shaped tube:

1. Solutes can pass through the selectively permeable membrane from right to left, but free water cannot.

   • This statement is false. Since arm B has a higher concentration of sugar, it likely contains solute molecules that cannot pass through the membrane if it is selectively permeable to water and not to solutes. Therefore, free water can move, but solutes will not move from arm B to arm A.

2. Water is tightly clustered around the hydrophilic solute molecules on both sides of the membrane.

   • This statement is true. In a solution, water molecules tend to form hydrogen bonds with hydrophilic (water-attracting) solute molecules, meaning they can be considered to be "clustered" around the solute.

3. There is more solute in the left arm of the tube than in the right arm of the tube.

   • This statement is false. Arm A has a lower concentration of sugar, meaning it has less solute compared to arm B, which has a higher concentration of sugar.

4. There is less free water in the right arm of the tube than in the left arm of the tube.

   • This statement is true. In the right arm (arm B), there is a higher concentration of sugar, which means there are more solute particles relative to free water molecules. Thus, the amount of free water would be lower in the right arm compared to the left arm.

Based on the evaluations above, the true statements are:

• Water is tightly clustered around the hydrophilic solute molecules on both sides of the membrane.
• There is less free water in the right arm of the tube than in the left arm of the tube.