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

40. According to the intermediate disturbance hypothesis, species richness is higher in areas of intermediate levels of disturbance. Why would species richness be lower at low levels of disturbance? (A) A high nutrient level poisons lots of species. (B) Competitive exclusion results in the extinction of species. (C) Ecological niches are less partitioned in places with high levels of disturbance. (D) Lack of disturbance slows down the evolution of new species. (E) Low level of disturbance results in low soil fertility.

41. Taxol is an anticancer drug extracted from the Pacific yew tree. In animal cells, Taxol disrupts microtubule formation by binding to microtubules and accelerating their assembly from the protein precursor, tubulin. Surprisingly, this stops mitosis. Specifically, Taxol must affect . (A) the formation of the mitotic spindle (B) anaphase (C) formation of the centrioles (D) chromatid assembly (E) the S phase of the cell cycle

42. Which of the following about transposable elements is correct? (A) occurs only in bacteria (B) occurs only in plants (C) moves genes between homologous regions of DNA (D) scatters genes to a new loci in the genome (E) plays little role in evolution

43. The difference between pinocytosis and receptor-mediated endocytosis is that ________ . (A) pinocytosis brings only water molecules into the cell, but receptor-mediated endocytosis brings in other molecules as well (B) pinocytosis increases the surface area of the plasma membrane whereas receptor-mediated endocytosis decreases the plasma membrane surface area (C) pinocytosis requires cellular energy, but receptor-mediated endocytosis does not (D) pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity (E) pinocytosis can concentrate substances from the extracellular fluid, but receptor-mediated endocytosis cannot

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

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

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 .