10. Why are action potentials usually conducted in only one direction along an axon?
(A) The nodes of Ranvier can conduct potentials in only one direction.
(B) The brief refractory period prevents reopening of voltage-gated Nat channels.
(C) The axon hillock has a higher membrane potential than the terminals of the axon.
(D) Ions can flow along the axon in only one direction.
(E) Voltage-gated channels for both Na⁺ and K⁺ open in only one direction.

6.When human beings choose a mate, they usually prefer people with the same skin color, same culture, same language, and similar living habits. Which of the following is related to this phenomenon? (A) panmixia (B) heterosis (C) outcrossing (D) backcrossing (E) assortative mating

7.Cytoskeleton of a eukaryotic cell is made up of (a)microtubule, (b)microfilament and (c)intermediated filaments. Which of them exhibits polarity? (A) a (B) b (C)c (D) a and b (E) b and c

8.Mitochondria are thought to be the descendants of certain alpha proteobacteria. They are, however, no longer able to lead independent lives because most genes originally present on their chromosomes have moved to the nuclear genome. Which phenomenon accounts for the movement of these genes? (A) homologous recombination (B) plasmolysis (C) horizontal gene transfer (D) conjugation (E) translation

9.What controls sex determination in American alligator? (A) Temperature (B) Behavioral interactions (C) Y Chromosome (D) Ratio of X chromosomes to autosomes (E) SRY gene

11. Which statement about biological homology is correct? (A) Paralogs: Insect wings and bat wings are both used for flight. (B) Orthologs: Humans use different MHC gene copies to identify different pathogens. (C) Analogs: The human eye is structurally similar to the octopus's eye. (D) Homologs: The needles of cacti (仙人掌) and hedgehogs (刺蝟) are used for physical defense. (E) Paralogs: Differentiation of the functions of the forelimb and hindlimb in humans.

12. Which of the following statements regarding photoperiodism is false? (A) Photoperiodism is the physiological reaction of organisms to the length of a dark period. It occurs in both plants and animals. (B) Many flowering plants (angiosperms) use photoreceptors such as phytochrome and cryptochrome to sense photoperiod. (C) Long-day plants flower when the night length falls below their critical photoperiod. (D) The shoot apical meristem that senses the photoperiod leading to its transition from a vegetative (leaf) bud to a reproductive (flower) bud. (E) Day-neutral plants such as maize do not initiate flowering based on photoperiodism.

13. All female mammals have one active X chromosome per cell instead of two. What causes this to happen? (A) attachment of methyl (-CH3) groups to the X chromosome that will remain active (B) only the X chromosome from mother will remain active (C) inactivation of the XIST gene on the X chromosome derived from the male parent (D) activation of the BARR gene on one X chromosome, which then becomes inactive (E) activation of the XIST gene on the X chromosome that will become the Barr body

14. A genetic map shows the map distance. The units of genetic distance are called map units (mu) or centiMorgans (cM). Which of the following indicates the map distance of 23.6 mu between two genes? (A) The distance between two genes is 23.6 millimeters. (B) There are 23.6 other genes between the two genes of interest. (C) The co-mutation rate of two genes is 23.6%. (D) The survival rate of the offspring is 23.6%. (E) 23.6% of the offspring exhibit recombination between the two genes.

15. A researcher is analyzing the immune response of a patient following the patient's exposure to an unknown agent while out of the country. The patient's blood is found to have a high proportion of lymphocytes with CD8 surface proteins. What is the likely cause? (A) The patient encountered a bacterial infection which elicited CD8 marked T cells. (B) The disease must have been caused by a multicellular parasite, such as can be encountered in polluted water sources. (C) The CD8 proteins would be discharged from these lymphocytes to lyse the infected cells. (D) The CD8 proteins marked the surfaces of cytotoxic 'T cells to attack virus-infected host cells. (E) CD8 marks the surface of cells that accumulate after the infection is over and signal patient recovery.

16. What is the name of the protein that is used to form the initial glycogen primer? (A) phosphoporin (B) glucokinase (C) glycoporin (D) glycogenin (E) pyrophorin