53. Which of the following statements is false?
(A) Estuaries support many semiaquatic species.
(B) Many lakes in temperate regions are characterized by seasonal thermal stratification.
(C) The distribution of photosynthetic organisms is limited by the quality and intensity of light in marine ecosystems.
(D) Estuaries usually contain no or few producers.
(E) Many aquatic biomes exhibit pronounced vertical stratification of chemical variables.

49. The vascular system of a three-year-old dicot stem consists of (A) 3 rings of xylem and 3 of phloem. (B) 2 rings of xylem and 2 of phloem. (C) 3 rings of xylem and 1 of phloem. (D) 1 rings of xylem and 3 of phloem. (E) 2 rings of xylem and 3 of phloem.

50. Within the female gametophyte, three mitotic divisions of the megaspore produce (A) the triple fushion nucleus and two synergids. (B) three pollen grains and three antipodal cells. (C) two antipodals and two eggs. (D) three antipodal cells,two polar nuclei, one egg, and two synergids. (E) a tube nucleus, a generative cell, an egg, and a sperm.

51. A pathogenic fungus invades a plant. Which of the following does the plant produce in response to the attack? (A) antibiotics (B) antisense RNA (C) phytochrome (D) phytoalexins (E) statoliths

52. Which of the following is correctly paired? (A) forebrain – diencephalons (B) midbrain – cerebellum (C) spinal cord – brainstem (D) both A and B are correct (E) both B and C are correct

54. The following organism with the greatest number of Hox genes should be a(n) (A) fish. (B) fly. (C) flatworm. (D) fluke. (E) fruit fly.

55. Which of the following does not have a coefficient of relatedness of 0.5 in humans? (A) a brother to his brother (B) a mother to her son (C) an uncle to his nephew (D) a father to his daughter (E) a sister to her brother

56. Which of the following is true in the logistic model of population growth? (A) as N approaches K, the growth rate will approach zero (B) as N approaches K, the death rate decreases (C) as N approaches K, the carrying capacity of the environment will increase (D) as N approaches K, the growth rate increases (E) both C and D are correct

57. The population cycle of the snowshoe hare and its predator indicates that (A) predators are not the only factor controlling the size of prey populations. (B) the two species must have evolved in close contact because one cannot live without the other. (C) both populations are controlled mainly by abiotic factors. (D) the hare populations is r-selected, whereas the lynx population is K-selected. (E) both C and D are correct.

58. A gastrovascular cavity, with a single opening, is the characteristic digestive system of animals in which phylum? (A) Nematoda (B) Platyhelminthes (C) Arthropoda (D) Mollusca (E) Porifera

59. Which of the following statements about endocrine system is false? (A) Hormones from the adrenal cortex control salt and water balance. (B) An increase in endorphins blocks pain. (C) An iodine deficiency might interfere with the production of thyroxine. (D) Some cells can conduct nerve signals and secrete hormones. (E) Most endocrine glands produce steroid hormones.