The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same.
-Refer to the figure. At the beginning of the experiment,
A) side A is hypertonic to side B.
B) side A is hypotonic to side B.
C) side A is isotonic to side B.
D) side A is hypertonic to side B with respect to glucose.
E) side A is hypotonic to side B with respect to NaCl.

Question

The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. 
-Refer to the figure. At the beginning of the experiment,
A) side A is hypertonic to side B. 
B) side A is hypotonic to side B. 
C) side A is isotonic to side B. 
D) side A is hypertonic to side B with respect to glucose. 
E) side A is hypotonic to side B with respect to NaCl.

Quizplus · Accepted Answer

A solution with lower solute concentration is hypotonic compared to a solution with a higher solute concentration. In Side A, the total solute concentration (0.9 M) is lower compared to the total solute concentration (1.2 M) in Side B. Hence, Side A is hypotonic to Side B. It is not possible to compare the tonicity with respect to glucose and NaCl separately since the membrane is permeable to both.

The Solutions in the Arms of a U-Tube Are Separated