39. X chromosome inactivation is an epigenetic mechanism that silences the majority of genes on one X chromosome. The inactivation appears to involve regions of .
(A) mutated genes
(B) intense transcription
(C) hyper-methylated DNA
(D) hypo-methylated DNA
(E) inverted genes

35. Which of the following is a true distinction between cellular respiration and lactate fermentation? (A) NADH is oxidized by the electron transport chain only in respiration. (B) Substrate-level phosphorylation is unique to lactate fermentation. (C) Only respiration oxidized glucose. (D) Respiration, but not lactate fermentation, is a catabolic pathway. (E) NAD+ functions as an oxidizing agent only in respiration.

36. Which of the following about cardiac muscle is correct? (A) They contract only when stimulated by neurons. (B) They lack an orderly arranged actin and myosin. (C) They lack the striations of skeletal muscle. (D) They have less sacroplasmic reticulum and thus contract more slowly than smooth muscle. (E) They are connected by intercalated discs, through which action potentials spread to all cells in the heart.

37. Which of the following short-distance transport routes in plants goes through plasmodesmata? (A) symplastic route (B) transmembrane route (C) apoplastic route (D) apoptosis route (E) aquaporin route

38. In the process of photosynthesis, which of the following is not involved in the creation of H+ gradient thylakoid lumen and stroma that generates ATP? (A) reduction of NADP+ (B) splitting of water in the thylakoid lumen (C) PQ cycle of the electron transport chain and its reaction to cytochrome b6f complex (D) regeneration of RuBP (E) electron transport

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

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