20. Which of the following definition is WRONG for molecular clock?
(A) Paralogous genes are used.
(B) Constant mutation rate is supposed.
(C) Fossil record can be used to correct dating.
(D) Based on Neutral theory.
(E) The rate of molecular change should be regular like a clock.

16. Which of the following statements about vitamins is FALSE? (A) Thiamine is a coenzyme in removing CO2 and relates to Beriberi. (B) Folic acid is a component of coenzyme A and relates to birth defect. (C) Ascorbic acid is a coenzyme in collagen synthesis and relates to scurvy. (D) Retinol is a component of visual pigments and relates to blindness. (E) Tocopherol is an antioxidant and relates to nervous system degeneration.

17. Pollen from a plant with the S1S2 genotype is recognized and allowed to germinate on the stigma of the same plant with the S1S2 genotype. According to the S-system hypothesis, this indicates that the plant is ______. (A) self-incompatible and must cross-pollinate (B) self-incompatible and can self-pollinate (C) self-compatible and must cross-pollinate (D) self-compatible and can self-pollinate (E) self-compatible and can self-pollinate or cross-pollinate

18. DNA methylation and histone acetylation are examples of ______. (A) genetic mutation (B) epigenetic phenomena (C) translocation (D) chromosomal rearrangements (E) gene degradation

19. Which of the following is in the correct order for one cycle of polymerase chain reaction (PCR)? (A) Denature DNA; add fresh enzyme; anneal primers; add dNTPs; extend primers. (B) Anneal primers; denature DNA; extend primers. (C) Denature DNA; anneal primers; extend primers. (D) Extend primers; anneal primers; denature DNA. (E) Add dNTPs; add fresh enzyme; denature DNA.

21. If organisms a, b, and c belong to the same class but to different orders and if organisms c, d, and e belong to the same order but to different families, which of the following pairs of organisms would be expected to show the greatest degree of structural homology? (A) a and d (B) b and c (C) b and d (D) d and e (E) a and e

22. Which of the following plants has a dominant sporophyte generation and a seed, but no fruit? (A) fern (B) pine tree (C) tulip (D) lycophyte (E) moss

23. Which of the following statements about renin-angiotensin-aldosterone system (RAAS) is FALSE? (A) Sensors in juxtaglomerular apparatus (JAG) detect decrease in pressure. (B) JAG releases renin with decreased pressure. (C) Renin cleaves angiotensinogen to produce angiotensin I. (D) Angiotensin II stimulates the kidney to release aldosterone. (E) Aldosterone increases blood volume by Na+ and water reabsorption.

24. A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following could the spider population be experiencing? (A) directional selection (B) genetic drift (C) disruptive selection (D) stabilizing selection (E) founder effect

25. Two species of frogs belonging to the same genus occasionally mate, but the embryos stop developing after a day and then die. These two frog species separate by ______. (A) gametic isolation (B) reduced hybrid fertility (C) hybrid breakdown (D) mechanical isolation (E) reduced hybrid viability

26. Which of the following characteristics tends to limit bryophytes and seedless vascular plants to habitats that are relatively moist? (A) absence of cuticle (B) presence of flagellated sperm (C) presence of free-living, independent zygotes and early embryos (D) presence of lignified vascular tissues (E) presence of seeds and pollen