46. Which of these is NOT found in the epidermis?
(A) stratified epithelium.
(B) blood vessels.
(C) tight cell junctions. 
(D) keratin.  
(E) melanin.

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.

47. The first vertebrates are most closely related phylogenetically to which of the following phyla? (A) Echinodermata. (B) Annelida. (C) Mollusca. (D) Arthropoda. (E) None of these.

48. The classic Hershey and Chase (1952) experiment which offered evidence in support of DNA being the genetic material in bacteriophage made use of which of the following labeled components? (A) phosphorus and sulfur. (B) phosphorus and nitrogen. (C) phosphorus and oxygen. (D) nitrogen and oxygen. (E) nitrogen and sulfur.

49. Which of the following terms best characterizes catabolite repression associated with the lactose operon in E. coli? (A) inducible system. (B) repressible system. (C) negative control. (D) positive control. (E) constitutive.

50. Developmental similarities observed in most vertebrates are probably due to (A) chance. (B) the similar environments in which they live. (C) homeoboxes. (D) their phylogenetic histories. (E) homeoboxes and their phylogenetic histories.

51. Which of the following statements concerning biogeochemical cycles is NOT correct? (A) Plants and algae can use two inorganic forms of nitrogen: ammonium and nitrate. (B) Photosynthesis by plants and phytoplankton removes substantial amounts of atmospheric CO2 each year. (C) The largest accumulations of phosphorus are in sedimentary rocks of marine origin. There are also large quantities of phosphorus in soils, in the oceans and in organisms. (D) Under anaerobic conditions, nitrifying bacteria use NO3- in their metabolism instead of O2, releasing N2 in a process known as nitrification. (E) The major pathway for nitrogen to enter an ecosystem is via nitrogen fixation, the conversion of N2 by bacteria to forms that can be used to synthesize nitrogenous organic compounds.

52. The breathing in human is controlled by all of the following mechanisms EXCEPT (A) The sensors in the walls of the aorta and carotid arteries in the neck detect changes in blood pH and send nerve impulses to the medulla. (B) The sensors in the aorta and carotid arteries also detect changes in O2 levels in the blood and signal the medulla to increase the breathing rate. (C) Nerves from a breathing control center in the medulla oblongata of the brain send impulses to the diaphragm and rib muscles, stimulating them to contract and causing inhalation. (D) Sensors in the medulla detect changes in the pH of the blood and interistial fluid bathing the surface of the brain. (E) The control center in the medulla sets the basic rhythm, and a control center in the pons moderates it, smoothing out the transitions between inhalations and exhalations.