BISC 307 – Spring 2009 Exam 1 Answers 1 Posted Answers.doc Page 1 of 6 3 pts. 4 pts. 3 pts. 4 pts. 6 pts. 1. Breathing raises the concentration of O2 in the blood, lowers the concentration of CO2 in the blood, and raises blood pH. According to the principles of negative feedback regulation, which one of the following is most likely to stimulate an increase in breathing? (d) a. an increase in blood O2 concentration b. a decrease in blood CO2 concentration c. an increase in blood pH d. none of the above would stimulate an increase in breathing 2. In a typical mammalian cell, which one of the following is most likely to occur if the Na+/K+ ATPase is inhibited with ouabain? (c) a. a decrease in intracellular [Na+] b. an increase in intracellular [K+] c. an increase in intracellular [Ca2+] d. an increase in Na+-glucose co-transport e. an increase in Na+-Ca2+ exchange 3. Which one of the following statements is false? (d) a. A slice of potato immersed in a hypotonic aqueous solution is likely to swell. b. Sodium-dependent glucose transport is an example of secondary active transport. c. The glucose transporter can move glucose in either direction across the plasma membrane. d. The symptoms of cystic fibrosis are consequences of a defect in the epithelial Na+ channel. e. Epithelial cells involved in the transport of water from one body compartment to another are likely to express aquaporin molecules. 4. Imagine two aqueous solutions, A and B, that are separated by a membrane that is permeable to K+ but not to Cl- or H2O. Solution A is 100 mM KCl, and solution B is 1 mM KCl. Which one of the following statements is most likely to be true? (e) a. Solution B is hyperosmotic compared to solution A. b. K+ ions will diffuse from solution A to solution B until the [K+] of both solutions is 50.5 mM. c. K+ ions will diffuse from solution B to solution A until the [K+] of both solutions is 50.5 mM. d. Over time, osmosis will increase the volume of solution A and decrease the volume of solution B. e. Solution A is electrically negative with respect to solution B. 5. The effects of hormones on target cells can be tremendously amplified by intracellular signaling pathways. In the case of the cAMP signaling pathway, which steps are responsible for this amplification? ANS: Amplification occurs at several steps. Binding of one hormone to its receptor can activate several stimulatory G-proteins. Each of these can activate several adenylyl cyclase enzymes, each of which generates many molecules of cAMP. These cAMP molecules in turn activate many protein kinase A molecules, each of which can phosphorylate many target proteins. Some of the target proteins may be enzymes, whose stimulated (or inhibited) activity further amplifies Exam6. When the neurotransmitter GABA binds to its postsynaptic receptors, the Cl- permeability of the postsynaptic membrane increases. In the adult mouse brain, this causes hyperpolarizing IPSPs. In young postnatal mice, however, GABA causes depolarizing EPSPs. Neuronal resting potentials are constant, at about -70 mV, and plasma [Cl-] does not change over the lifespan. Which one of the following statements best explains how GABA shifts from having an excitatory action to an inhibitory action? (d) a. In young mice, GABA stimulates an active transporter that pumps Cl- in. b. In young mice, the GABA-activated channel is permeable to Na+ as well as Cl-. c. In young mice, the GABA-activated channel is permeable to K+ as well as Cl-. d. Intracellular [Cl-] is high in young mice, and lower in adult mice. e. None of the above explains the developmental shift in GABA’s action. 7. Indicate the immediate effect of each of the manipulations below on the resting membrane potential of a typical neuron by writing D (for depolarization), H (for hyperpolarization), or NC (for no change) in the blanks. Write only one answer in each blank. ANS: a-NC, b-D, c-H, d-D ______ a. Exposure to tetrodotoxin. ______ b. An increase in extracellular K+ concentration. ______ c. Opening of Cl- channels, if ECl is more negative than the membrane potential. ______ d. Opening an equal number of Na+ and K+ channels. 8. 1 Posted Answers.doc Page 2 of 6 1 2 3 ______ a. Area where, for most voltage-gated Na+ channels, both the activation and inactivation gates are open. ______ b. Area where most voltage-gated Na+ channels are closed, and outward flow of current is depolarizing the membrane. ______ c. Area where, for most voltage-gated Na+ channels, the activation gate is open but the inactivation gate is closed. ______ d. Area where all channels are in their resting configuration. ______ e. Area where only voltage-gated K+ channels (delayed rectifier channels) are open. 9. Imagine that you isolate a single axon and arrange it on stimulating electrodes as shown in the diagram below. The cell body, or soma, end is to the left and the presynaptic terminal end is to the right. You then stimulate both ends simultaneously, to elicit an action potential at each end. Which one of the following best describes what would happen to the action potentials when they propagate to the middle of the axon and meet? (a) EK ENa ECl 0 + Vm -Distance along axon 4 5 The diagram on the right shows a segment of a squid axon through which an action potential is propagating, in the direction shown. The graph below shows the value of the membrane potential at various positions along the axon. The horizontal axes of the graph and the drawing correspond. Areas 1-5 are particular locations along the axon. Answer each question below by writing one number in the blank. ANS: a-4, b-5, c-3, d-1, e-2 5 pts. 4 pts. 5 pts. 4 pts. propagation direction ExamStimulate Stimulate SOMA END TERMINAL END a. The action potentials will cancel when they collide; they will not propagate past the midpoint. b. The action potentials will sum temporally, creating an action potential roughly twice as large. c. Each action potential will pass through the other and propagate to the opposite end of the axon. d. The action potentials will never meet, because they can only propagate in the normal direction (soma → terminal). 10. Which of the following is not a general characteristic of postsynaptic potentials (PSPs)? (a) 3 pts. 10 pts. 6 pts. 9 pts. a. PSPs are all-or-none in amplitude. b. PSPs decrease in amplitude with distance away from the synapse. c. PSPs are produced by neurotransmitter