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UCD NPB 101 - NPB 101 Sample Midterm I

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NPB 101 Sample Midterm I Identify the letter of the choice that best completes the statement or answers the question. 1. Which of the following statements is incorrect? (a) negative feedback tends to maintain a controlled factor in a steady state. (b) positive feedback tends to move a controlled variable away from a steady state. (c) homeostasis is the dynamic maintenance of a stable internal (extracellular) environment within the organism. (d) homeostasis relies primarily on positive feedback. (e) each cell in the body depends on homeostasis for its own survival. 2. Select the association that most accurately reflects organelle function (a) ribosome/protein production. (b) golgi/detoxification. (c) mitochondria/transcription. (d) lysosome/ATP production. (e) peroxisome/exocytosis. 3. The phospholipids within the plasma membrane (a) form channels for passage of small ions. (b) form channels for passage of large molecules such as glucose. (c) serve as a barrier to passage of water-soluble substances between the ICF (intracellular fluid) and ECF (extracellular fluid). (d) both (a) and (c). (e) none of these answers. 4. Extracellular chemical messengers (a) are secreted by one cell and detected by another. (b) can act on target cells that are adjacent to or distant from the secretory cell. (c) can exert their effects on the target cell by opening or closing of specific channels to regulate ionic movement across the plasma membrane. (d) can exert their effects on the target cell by activating intracellular second messenger systems. (e) all of these answers. 5. If pure water and a solution containing a solute are separated by a membrane that is permeable to water but not the solute: (a) water molecules will move across the membrane, though only in one direction. (b) both water and solute will diffuse across the membrane until a state of equilibrium is established. (c) there will be net movement of water from the side containing the pure water to the side containing the solution. (d) there will be net movement of water from the side containing the solution to the side containing pure water. (e) inevitably, the membrane will rupture. 6. In carrier-mediated transport: (a) energy (ATP) is directly used to transport molecules downhill, from an area of higher to lower concentration. (b) energy (ATP) is directly used to alter the affinity of the carrier’s binding site. (c) energy (ATP) to directly used to flip carrier orientation. (d) both (a) and (b). (e) both (a) and (c). 7. Which of the following statements concerning the Na+-K+ pump is correct? (a) the dephosphorylated conformation (occurs when exposed to the ECF) of the Na+-K+ pump has low affinity for K+. (b) the phosphorylated conformation (occurs when exposed to the ICF) of the Na+-K+ pump has low affinity for Na+. (c) the phosphorylated conformation (occurs when exposed to the ICF) of the Na+-K+ pump has high affinity for K+. (d) the dephosphorylated conformation (occurs when exposed to the ECF) of the Na+-K+ pump has high affinity for Na+. (e) none of these answers. 8. Which of the following statements best describes the equilibrium potential of an ion (such as ENa+ or EK+)? (a) the voltage across the plasma membrane that occurs at resting potential. (b) the voltage across the plasma membrane that exactly opposes in direction and magnitude the net diffusion of that ion down its concentration gradient. (c) the voltage across the plasma membrane that prevents the Na+/K+ pump from operating. (d) the voltage in the bulk solution on either side of the membrane. (e) the voltage across the plasma membrane that stops all flow of that ion across the membrane.9. Select the correct statement(s) regarding the membrane potential (a) at the resting potential, the net driving force on Na+ is stronger than the net driving force on K+. (b) at the resting potential, the driving force on K+ due to its concentration gradient exactly opposes in direction and magnitude the driving force due to the electrical gradient. (c) at the resting potential, the driving force on Na+ due to its concentration gradient exactly opposes in direction and magnitude the driving force due to the electrical gradient. (d) both (a) and (c). (e) all of these answers. 10. Which of the following statements best describes graded potentials? (a) graded potentials result from passive current flow away from a discrete event. (b) graded potentials occurring on nearby parts of the neuron may sum together. (c) graded potentials can be either depolarizing or hyperpolarizing (d) none of these answers. (e) all of these answers. 11. Which of the following best describes the sequence of events that occurs when a neuron fires an action potential? (a) During the rising phase of the spike, K+ channels are gated open by depolarization and K+ flows into the cell. The resulting depolarization causes the K+ channels to rapidly inactivate, preventing any further entry of K+ ions into the cell. At the same time, but at a slower rate, Na+ channels are gated open by the depolarization, Na+ flows out of the cell and this causes the membrane potential to repolarize. (b) During the rising phase of the spike, Na+ channels inactivate and prevent Na+ from entering the cell. At the same time, K+ channels are gated open by the depolarization, K+ flows into the cell causing the membrane potential to depolarize further. The depolarization causes the K+ channels to inactivate and this causes the membrane potential to repolarize. (c) During the rising phase of the spike, Na+ channels are gated open by depolarization and Na+ flows into the cell. The resulting depolarization causes the Na+ channels to rapidly inactivate, preventing any further entry of Na+ into the cell. At the same time, but at a slower rate, K+ channels are gated open by the depolarization, K+ flows out of the cell and this causes the membrane potential to repolarize. (d) During the rising phase of the spike, Na+ channels are gated open by depolarization and Na+ flows out of the cell. The resulting hyperpolarization causes the Na+ channels to rapidly inactivate, preventing any further flow of Na+ out of the cell. At the same time, but at a slower rate, K+ channels are gated open by the depolarization, K+ flows into the cell and this causes the membrane potential to depolarize. 12. At the peak of an action potential, (a) the electrical


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