22. The relatively short interval of time (535–525 million years ago) during which large forms of many present-day animal phyla first appear in the fossil record is known as what?
(A) The Permian extinction
(B) The Cambrian explosion
(C) The Mesozoic era
(D) The colonization of land

18. A water-soluble hormone typically acts on a target cell by:(A) binding to a receptor inside the cell to alter gene expression.(B) binding to a cell-surface receptor to trigger an intracellular signal transduction pathway.(C) diffusing across the plasma membrane to directly activate enzymes.(D) being converted into a lipid-soluble form before entering the cell.

19. Different species of fruit flies that live in the same parts of the Hawaiian Islands have distinct, elaborate courtship rituals.What type of reproductive isolation does this represent?(A) Habitat isolation (B) Temporal isolation (C) Behavioral isolation (D) Gametic isolation

20. Genes A, B, and C are located on the same chromosome. Testcrosses show that the recombination frequency between A andB is 28% and that between A and C is 12%. Which of the following statements about the order of these genes on thechromosome is most likely correct?(A) The order is A-B-C. (B) The order is A-C-B.(C) The order is B-A-C. (D) The order cannot be determined from this data alone.

21. If a diploid cell in the G1 phase of the cell cycle has a DNA content of 'x', what would be the DNA content of the same cell at metaphase of meiosis I?(A) 0.25x (B) 0.5x (C) x (D) 2x

23. How might an error during meiosis lead to polyploidy in plants?(A) Failure of homologous chromosomes to separate during meiosis I, leading to diploid gametes.(B) Random assortment of chromosomes during metaphase I, resulting in gametes with extra chromosomes.(C) Crossing over between non-sister chromatids, creating recombinant chromosomes.(D) Nondisjunction in mitosis during gamete formation in the diploid organism.

24. A population has an allele 'a' with a frequency of 0.45. If the population is in Hardy-Weinberg equilibrium, what is the expected frequency of the homozygous dominant genotype (AA)?(A) 0.2025 (B) 0.3025 (C) 0.4950 (D) 0.5500

25. According to the principle of maximum parsimony, when considering multiple phylogenetic hypotheses, which explanation should systematists investigate first?(A) The most complex explanation consistent with all known facts.(B) The explanation that incorporates the most recently discovered genetic mutations.(C) The simplest explanation that is consistent with the facts.(D) The explanation that best aligns with previously established taxonomic classifications.

26. Two organisms, with genotypes BbDD and BBDd, are mated. Assuming independent assortment of the B/b and D/d genes,what is the probability of obtaining an offspring with the genotype BbDd?(A) 1/16 (B) 1/8 (C) 1/4 (D) 1/2

27. Which of the following characteristics, structures, or processes is common to both bacteria and viruses?(A) Metabolism (B) Ribosomes(C) Genetic material composed of nucleic acid (D) Cell division

28. Which type of sensory receptor detects physical deformation in the body's environment associated with pressure, touch,stretch, motion, or sound?(A) Chemoreceptor (B) Electromagnetic receptor(C) Nociceptor (D) Mechanoreceptor