Practise AP Biology 2.7 questions by connecting tonicity, water-potential gradients and osmoregulatory mechanisms such as contractile vacuoles, ADH and aquaporins.
A student placed a semipermeable membrane inside a U-shaped channel with two chambers, as shown. The membrane permits the movement of water but not salt. The student wants to vary the rate of osmosis that occurs across the membrane. Which of the following experimental designs will result in the fastest net rate of water movement into chamber A?
Placing salt water in chamber A and distilled water in chamber B
Placing distilled water in both chambers
Placing distilled water in chamber A and salt water in chamber B
Placing salt water in both chambers
Questions 13-18 A student peeled the skins from grapes, exposing cells with membranes that are only permeable to water and small diffusible solutes. The student measured the mass of the peeled grapes. The student then placed each peeled grape into one of five solutions. After 24 hours, the student removed the peeled grapes from the solutions, measured their final mass, and calculated the percent change in mass (Table 1).
TABLE 1. PERCENT CHANGE IN MASS OF PEELED GRAPES IN SOLUTIONS
In a second experiment (Table 2), the student placed a peeled grape into a solution containing both small diffusible solutes and solutes to which the membrane is impermeable (nondiffusible solutes).
TABLE 2. CONCENTRATION OF SOLUTES IN SECOND EXPERIMENT
Assuming a negligible pressure potential, which of the following best predicts the net movement of the small diffusible solutes and water in the second experiment (Table 2) ?
Small diffusible solutes will diffuse into the grape cells, followed by water.
Small diffusible solutes will diffuse out of the grape cells and water will diffuse into the cells.
Small diffusible solutes will diffuse out of the grape cells, followed by water.
Small diffusible solutes will diffuse into the grape cells and water will diffuse out of the cells.