48. Stem cell transplants may someday be used to treat Parkinson's disease. Researchers are hopeful that these cells would alleviate the symptoms of Parkinson's disease by ________.
(A) preventing temporal lobe seizures
(B) repairing sites of traumatic brain injury
(C) replenishing missing ion channels
(D) secreting the neurotransmitter dopamine
(E) changing in myelination of axons

44. How does extracellular glucose inhibit transcription of the lac operon? (A) by strengthening the binding of the repressor to the operator (B) by weakening the binding of the repressor to the operator (C) by degrading the lac operon gene (D) by inhibiting RNA polymerase from opening the strands of DNA to initiate transcription (E) by reducing the levels of intracellular cAMP

45. Which of the following traits do archaeans and bacteria share? 1. composition of the cell wall 2. presence of plasma membrane 3. lack of a nuclear envelope 4. identical rRNA sequences (A) 1 and 2 (B) 1 and 3 (C) 1 and 4 (D) 2 and 3 (E) 2 and 4

46. Asbestos is a material that was once used extensively in construction. One risk from working in a building that contains asbestos is the development of asbestosis caused by the inhalation of asbestos fibers. Cells will take up asbestos by phagocytosis, but are not able to degrade it. As a result, asbestos fibers accumulate in ________. (A) rough ER (B) lysosomes (C) Golgi apparatus (D) nuclear (E) peroxisomes

47. Which of the following is more likely an application of the concept of molecular clock? (A) estimate the origin time of HIV virus (B) estimate the vertical migration pattern of benthic diatoms (C) estimate the rhythmic behaviors of intertidal species in the lab (D) estimate the genetic diversity of a population (E) estimate the reason for dinosaur extinction

49. Prezygotic isolating mechanisms act to limit hybridization and maintain the genetic identity of closely-related species. For sympatric corals that do synchronized spawning, what is the most likely isolation mechanism? (A) behavioral isolation (B) temporal isolation (C) habitat isolation (D) gametic isolation (E) hybrid breakdown

50. How does a noncompetitive inhibitor decrease the rate of an enzyme reaction? (A) by binding to the active site of the enzyme, thus preventing binding of the normal substrate (B) by binding to an allosteric site, thus changing the shape of the active site of the enzyme (C) by decreasing the free-energy change of the reaction catalyzed by the enzyme (D) by acting as a coenzyme for the reaction (E) by binding to the substrate, thus changing its shape so that it no longer binds to the active site of the enzyme .

51. Which of the following statements regarding insects is correct? (A) Incomplete metamorphosis have a pupal stage. (B) Metamorphosis from the larval stages to the adult occurs during pupal stage. (C) Insects are analids. (D) Book lung is a special organ in insects. (E) Insects are lophotrochozoa.

52. Which of the following correctly describes the relationships between gross primary production (GPP), net primary production (NPP), autotrophic respiration (Ra), net ecosystem production (NEP) and total respiration of all organisms in the ecosystem (Rt)? (A) NPP = GPP - Rt (B) GPP = NPP - NEP (C) Rt + Ra + NPP = GPP (D) NPP = GPP - Ra (E) GPP = NEP + Rh

53. Which of the following statements regarding vertebrates is correct? (A) Chondrichthyans have operculum. (B) Amphibians are amniotes. (C) Marsupials have fully developed placenta. (D) Osteichthyans have swim bladders. (E) None of the above.

54. Which of the following descriptions regarding appetite control of animal is correct? (A) Ghrelin is produced by small intestine. (B) Leptin triggers the feelings of hunger. (C) Insulin suppresses appetite by acting on intestine directly. (D) PYY acts as appetite suppressant. (E) None of the above.