43. Sensory transduction of light/dark information in the vertebrate retina is accomplished by
(A) rods and cones
(B) horizontal cells
(C)amacrine cells
(D) ganglion cells
(E)bipolar cells

39. How do T cell receptor recognize antigen? (A) Antigen receptors of T cell bind to antigens on the surface of a virus. (B) the antigen receptors on the surface of the helper T cell bind to antigen fragments complex with class-I MHC molecules on the antigen-presenting cell. (C)accessory protein CD8 on the helper T cell surface binds to the MHC molecules, helping keep the cell-cells joined. (D) an antigen fragment binds to an MHC molecule and then displayed to the cell surface. The combination of MHC molecule and antigen is recognized by T cell. (E)None of the above.

40. The major function of the colon is the absorption of _______ and _______. (A) minerals； water (B) peptides； minerals (C)water； vitamins (D) minerals； vitamins (E)peptides； vitamins

41. Which one of the following statements is NOT true? (A) Most of CO2 from respiring cells diffuses into the blood and is transported in solution in blood plasma. (B) Nitric oxide (NO) is a major inducer of vasodilation. (C)The medulla regulates the rate and depth of breathing in response to pH changes in the cerebrospinal fluid. (D) Return of blood to the heart can be enhanced by contraction of smooth muscle in venule walls and skeletal muscle contraction. (E)None of the above.

42. Which one of the following statements is not true? (A) The development of body organs of a human embryo mainly occurs in the first 3 months of pregnancy. (B) During human pregnancy, the function of mucus plugs in the cervix is to prevent a second fertilization. (C)About 24 hrs after fertilization, the zygote begins to divide by mitosis without changes in embryo size. (D) In human pregnancy, the mother's blood contains DNA from the fetus. (E)All of the above.

44. The amnion cells of human embryos are derived from___________. (A) hypoblasts (B) epiblasts (C)trophoblasts (D) allantois (E)None of the above.

45. Signals from _______ induce cells above to become cells of neural plate. (A) archenteron (B) vegetal pole (C)yolk sac (D) notochord (E)None of the above.

46. What happens when a resting neuron's membrane depolarizes? (A) There is a net diffusion of Na+ out of the cell. (B) The equilibrium potential for K+ (EK) becomes more positive. (C)The neuron's membrane voltage becomes more positive. (D) The cell's inside is more negative than the outside. (E)None of the above.

47. Which of the following statements about action potentials is correct? (A) Action potentials for a given neuron vary in magnitude. (B) Action potentials for a given neuron vary in duration. (C)Action potentials are propagated down the length of the axon. (D) Movement of ions during the action potential occurs mostly through the sodium pump. (E)None of the above.

48. Which of the following is a potential problem associated with genetically engineered plants? (A) Disease resistance genes may escape into the wild. (B) It will be difficult to breed engineered plants with natural types. (C)Engineered plants will be less nutritious. (D) Genetically engineered plants will not be able to reproduce on their own. (E)All of the above.

49. Scientists believe that the direction birds go when migrating is guided in part by ________. I) the stars in the night sky  II) the sun during the day  III) the magnetic field of the Earth (A) only I (B) only II (C)only III (D) I, II, and III (E)None.