Answers to Chapter Five

ANSWERS TO CHAPTER FIVE

1. Answer: d. In any system, including biological systems, the act of osmosis happens to solvents only. In biological systems, the solvent is always water. 2. Answer: a. Lipids are hydrophobic; therefore, they cross the cell membrane easily. Small gaseous molecules are also permeable across the membrane.

Glucose, amino acids, and ions like sodium are not able to cross the membrane without assistance. 3. Answer: b. The driving force behind simple diffusion is the concentration gradient. The substance will go from a high concentration to a low concentration, regardless of the type of solute. 4. Answer: a. Oxygen can pass through the membrane without the use of a channel of any kind. This means that it can pass via simple diffusion. The others involve active transport or facilitated diffusion because ion channels are necessary to allow these to get through the nonpolar membrane. 5. Answer: c. The P-pump is the main category of pump that belongs to the class of pumps known as sodium-potassium ATPase pumps. 6. Answer: a. The V-pump will only pump hydrogen ions across the membranes of vacuoles, endosomes, and lysosomes, allowing for the inside of the structures to have a lower pH for the function of enzymes within them. 7. Answer: c. With an antiporter system, the energy is gotten from the electrochemical gradient produced by sodium. Sodium diffuses back into the cell, while calcium is pumped out of the cell in this process. 8. Answer: a. The glucose-sodium transport is a symporter mechanism in which the sodium and glucose both get transported in the same direction. 9. Answer: b. The nerve cell depolarizes when the voltage-gated sodium channels open up and allow sodium to enter the cell. 10. Answer: c. There are voltage-gated potassium channels that allow potassium to leave the cell so that it becomes more electronegative again. Once this has occurred, the channels close and the sodium-potassium ATPase pump reestablishes the resting potential.