27. Trace elements are those required by organisms in only minute quantities. Which of the following is a trace element that is required by humans and other vertebrates?
(A) nitrogen
(B) calcium
(C) iodine
(D) sodium
(E) phosphorus

23. What is a genome? (A) An ordered display of chromosomes arranged from largest to smallest. (B) A specific set of polypeptides within each cell. (C) A specialized polymer of four different kinds of monomers. (D) A specific segment of DNA that is found within a prokaryotic chromosome. (E) The complete complement of an organism's genes.

24. Why are cattle able to survive on a diet consisting almost entirely of plant material? (A) They are autotrophic. (B) Cattle, like the rabbit, reingest their feces. (C) They manufacture all 15 amino acids out of sugars in the liver. (D) Cattle saliva has enzymes capable of digesting cellulose. (E) They have cellulose-digesting, symbiotic microorganisms in chambers of their stomachs.

25. Which one of the following, if present in a urine sample, would likely be caused by trauma? (A) amino acids (B) glucose (C) salts (D) erythrocytes (E) vitamins

26. The main source of energy for producers in an ecosystem is (A) light energy. (B) kinetic energy. (C) thermal energy. (D) chemical energy. (E) ATP.

28. Which of the following pieces of evidence most strongly supports the common origin of all life on Earth? (A) All organisms require energy. (B) All organisms show heritable variation. (C) All organisms reproduce. (D) All organisms use essentially the same genetic code. (E) All organisms have undergone evolution.

29. Which of these is the smallest unit upon which natural selection directly acts? (A) a species' gene frequency (B) a population's gene frequency (C) an individual's genome (D) an individual's genotype (E) an individual's phenotype

30. The higher the proportion of loci that are "fixed" in a population, the lower is that population's (A) nucleotide variability. (B) genetic polyploidy. (C) average heterozygosity. (D) A, B, and C (E) A and C only

31. Which of these should decline in hybrid zones where reinforcement is occurring? (A) gene flow between distinct gene pools (B) speciation (C) the genetic distinctness of two gene pools (D) mutation rate (E) hybrid sterility

32. The largest unit within which gene flow can readily occur is a (A) population. (B) species. (C) genus. (D) hybrid. (E) phylum.

33. Which statement represents the best explanation for the observation that the nuclear DNA of wolves and domestic dogs has a very high degree of homology? (A) Dogs and wolves have very similar morphologies. (B) Dogs and wolves belong to the same order. (C) Dogs and wolves are both members of the order Carnivora. (D) Dogs and wolves shared a common ancestor very recently. (E) Convergent evolution has occurred.