SAT Subject Biology Practice Question 367: Answer and Explanation
17. Dialysis tubing is a semipermeable membrane. It allows small molecules, such as water, to pass through easily, while larger molecules, such as sucrose, are restricted. Movement of molecules across the tubing is due to concentration gradients. In an experiment designed to study osmosis, several pieces of dialysis tubing were filled with sucrose solutions of varying concentration and placed in beakers containing distilled water. The rate and direction of water movement was determined by weighing the bags before and after placing them in the distilled water. The data are recorded below.
Why does the mass of Tube 3 increase while the mass of Tube 4 decreases?
A. Water is moving into Tube 3, and sucrose is moving into Tube 4.
B. Water is moving into Tube 4, and sucrose is moving into Tube 3.
C. Water is moving into Tube 3, and water is moving out of Tube 4.
D. Sucrose is moving into Tube 3, and sucrose is moving out of Tube 4.
E. Sucrose is moving out of Tube 3, and water is moving out of Tube 4.
Correct Answer: C
C Sucrose cannot cross the dialysis membrane, so it cannot cause any effect on the mass of the tubes. This eliminates choices A, B, D, and E.