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

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

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

27. There are several stages about alternation of generations of ferns. Which order is TRUE? (1) gametophyte, (2) sporophyte, (3) spores, (4) archegonia, (5) gametes. (A) 32541 (B) 23145 (C) 32451 (D) 23541 (E) 32145

28. Compare with Monocots and Eudicots, which of the following statements is FALSE? (A) A seed of Monocots has one cotyledon; that of Eudicots has two. (B) Leaf vein of Monocots is usually parallel, but that of Eudicots is usually netlike. (C) Vascular tissue of stems in Monocots is scattered, but that of Eudicots is usually arranged in ring. (D) Pollen grain of Monocots has one opening; that of Eudicots has three openings. (E) Floral organs usually in multiple of four in Monocots, but three in Eudicots.

29. Which structure is found in angiosperms but NOT gymnosperms? (A) fruit (B) spores (C) seeds (D) ovule (E) a tube that grows from the pollen to deliver sperm

30. The heterokaryotic phase of a fungal life cycle is ______. (A) a stage in which the hyphae contain only one type of haploid nucleus (B) a stage in which hyphae contain two, genetically different, haploid nuclei (C) a stage in which hyphae contain two, genetically different, diploid nuclei (D) a stage that is diploid but functions as a gametophyte (like the body of an animal) (E) a triploid stage formed by the fusion of a diploid nucleus with the haploid nucleus of a compatible hypha

31. Exercise and emergency reactions include ______. (A) decreased activity in the sympathetic, and increased activity in the parasympathetic divisions (B) increased activity in all parts of the peripheral nervous system (C) increased activity in the sympathetic, and decreased activity in the parasympathetic divisions (D) increased activity in the enteric nervous system (E) reduced heart rate and blood pressure