39. Neurons at rest are not at the equilibrium potential for K⁺ because the cell membrane is
(A) only permeable to K⁺.
(B) slightly permeable to Na⁺.
(C) not permeable to Na⁺.
(D) not permeable to K⁺.
(E) only permeable to Na⁺.

35. Reproduction isolation resulting from behavioral changes that inhibit mating between neighbors can lead to (A) hybrid vigor. (B) allopatric speciation. (C) sympatric speciation. (D) stabilizing selection. (E) directional selection.

36. Two islands that are similar in size and have the same distance from the mainland have very different species richness. According to the theory of island biogeography, the difference in species richness is probably due to (A) area effect. (B) distance effect. (C) habitat effect. (D) target effect. (E) rescue effect.

37. Wbich of the following is NOT true about estruaries? (A) Estuaries have lower net primary production than continentia} shelf. (B) Estuaries are susceptible to pollution and commercial developments by humans. (C) Estuaries support a variety of animal life that humans consume. (D) Estuaries are often bordered by mudflats and salt marshes. (E) Estuaries contain waters of varying salinity.

38. The perceived pitch of a sound depends on (A) vibrations of the tympanic membrane being transmitted through the incus. (B) vibrations of the oval window creating wave formation in the fluid of the vestibular canal. (C) the region of the basilar membrane where the signal originated. (D) A and C only. (E) A, B, and C.

40. 'Which of the following mechanisms for osmoregulation or nitrogen removal is INCORRECTLY paired with its corresponding animal? (A) metanephridium-earthworm. (B) Malpighian tubule-insect. (C) kidney-frog. (D) flame bulb-snake. (E) direct cellular exchange-marine invertebrate.

41. 'Which of the following respiratory systems is not closely associated with a blood supply? (A) vertebrate lungs. (B) fish gills. (C) tracheal systems of insects. (D) the outer skin of an earthworm. (E) the parapodia of a polychaete worm.

42. Where do air-breathing insects carry out gas exchange? (A) in specialized external gills. (B) in specialized internal gills. (C) in the alveoli of their lungs. (D) across the membranes of cells. (E) across the thin cuticular exoskeleton.

43. A mutation results in a cell that no longer produces a normal protein kinase for the M phase checkpoint. Which of the following would likely be the immediate result of this mutation? (A) The cell would prematurely enter anaphase. (B) The cell would never leave metaphase. (C) The cell would never enter metaphase. (D) The cell would never enter prophase. (E) The cell would undergo normal mitosis, but fail to enter the next G1 phase.

44. 'When nutrients are supplied to a cell, the last fluid through which they must pass before encountering the plasma membrane is the (A) plasma. (B) interstitial fluid. (C) blood. (D) intracellular fluid. (E) cerebrospinal fluid.

45. During meiosis ll, (A) cytokinesis results in the formation of a total of two cells. (B) sister chrorriatids of each chromosome are separated from each other. (C) homologous chromosomes pair up. (D) homologous chromosomes separate. (E) sister chromatids exchange parts.