SAT Subject Biology Practice Question 369: Answer and Explanation
19. 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.
Which of the following graphs best illustrates the relationship between Tube 2 and Tube 3 ?
Correct Answer: B
B The gradient in Tube 3 is much larger than the gradient in Tube 2, thus water would be expected to enter more rapidly. This is confirmed by the data in Table 1. A linear graph should show two lines with positive slopes, and the slope of Tube 3's line should be greater than the slope of Tube 2's line.