Sucrose Transport into Cells: Experimental Treatments and Membrane Structure

1. Chapter 7 0 Membrane Structureand Function

2. Based on the model of sucrose uptake in this figure, which of the following experimental treatments would increase the rate of sucrose transport into the cell? decreasing extracellular sucrose concentration decreasing extracellular pH decreasing cytoplasmic pH adding an inhibitor that blocks the regeneration of ATP adding a substance that makes the membrane more permeable to hydrogen ions 0

3. 0 • The carbohydrates attached to some of the proteins and lipids of the cell membrane are added as the membrane is refined in the Golgi apparatus; the new membrane then forms transport vesicles that travel to the cell surface. On which side of the vesicle membrane are the carbohydrates? • Interior surface of the vesicle membrane • Exterior (cytoplasmic) surface of the vesicle membrane

4. For Questions 3-7 0 An artificial cell consisting of an aqueous solution enclosed in a selectively permeable membrane has just been immersed in a beaker containing a different solution. The membrane is permeable to water and to the simple sugars glucose and fructose but completely impermeable to the disaccharide sucrose.

5. Which solute(s) will exhibit a net diffusion into the cell? sucrose glucose fructose 0

6. Which solute(s) will exhibit a net diffusion out of the cell? sucrose glucose fructose 0

7. Which solution is hypertonic to the other? the cell contents the environment 0

8. In which direction will there be a net osmotic movement of water? out of the cell into the cell neither 0

9. A solution of 1 M glucose is separated by a selectively permeable membrane from a solution of 0.2 M fructose and 0.7 M sucrose. The membrane is not permeable to the sugar molecules. Which of the following statements is correct? Side A is hypotonic relative to side B. The net movement of water will be from side B to side A. The net movement of water will be from side A to side B. Side B is hypertonic relative to side A. There will be no net movementof water. 0

10. 0 • You observe plant cells under a microscope that have just been placed in an unknown solution. First the cells plasmolyze; after a few minutes, the plasmolysis reverses and the cells appear normal. What would you conclude about the unknown solute? • It is hypertonic to the plant cells, and its solute can not cross the pant cell membranes. • It is hypotonic to the plant cells, and its solute can not cross the pant cell membranes. • It is isotonic to the plant cells, but its solute can cross the plant cell membranes. • It is hypertonic to the plant cells, but its solute can cross the plant cell membranes. • It is hypotonic to the plant cells, but its solute can cross the plant cell membranes.

11. An experiment is designed to study the mechanism of sucrose uptake by plant cells. Cells are immersed in a sucrose solution, and the pH of the solution is monitored with a pH meter. Samples of the cells are taken at intervals, and the sucrose in the sampled cells is measured. The measurements show that sucrose uptake by the cells correlates with a rise in the pH of the surrounding solution. The magnitude of the pH change is proportional to the starting concentration of sucrose in the extracellular solution. A metabolic poison known to block the ability of cells to regenerate ATP is found to inhibit the pH changes in the extracellular solution. Based on this information which of the following statements would you predict is correct? * Sucrose uptake is the result of simple diffusion Hydrogen ion movement is the result of facilitated diffusion. Sucrose moving through the membrane forces hydrogen ions in to the cell Sucrose and Hydrogen ions are transported in opposite directions across the membrane Sucrose transport is the result of a hydrogen ion contransporter. 0