24. The immediate, direct effect of auxin in cell elongation, according to the acid growth hypothesis, is to
(A) increase the hydrostatic pressure in cells, stretching their walls.
(B) activate ATP-driven proton (H⁺) pumps, and result in an accumulation of H⁺ in cytoplasm. 
(C) shift the pH and thus activate enzymes that break the hydrogen bonds.
(D) move water into vacuoles.
(E) activate the synthesis of new cytoplasm.

20. 'Which of the following statements is most compatible with the "source-sink" concept of sugar transport in the phloem? (A) Sugars are loaded at the sink. (B) Sugars move from the sink to the source in the phloem. (C) Sugars are unloaded at the source. (D) Developing young leaves are sinks and fully developed leaves are sources. (E) Transport is always unidirectional in the phloem.

21. The completion of the S phase of the cell cycle of a mammalian cell is marked by all of the following EXCEPT: (A) Histone content per cell is double that of cells in G1• (B) In replicated DNA, newly incorporated bases are paired with parental bases. (C) Each replicated chromosome has four telomeres. (D) Sister chromatids disjoin from one another. (E) The nucleus contains the equivalent amount of DNA of a tetraploid cell in G1•

22. Collenchyma cells can be recognized by (A) lignin in the cell walls.(B) the presence of chloroplasts. (C) their unevenly thickened cell walls.(D) the lack of nuclei at maturity. (E) large central vacuoles.  

23. Which of the following is a land plant that produces flagellated sperm and has a sporophyte-dominant life cycle? (A) fern. (B) moss. (C) liverwort. (D) charophycean. (E) hornwort.

25. A precursor in the synthesis of the peptidoglycan of bacterial cell walls is UDP-: (A) galactose. (B) glucose.(C) glucuronic acid. (D) N-acetylglucosamine. (E) penicillin. 

26. ___ ecologists would study the distribution of Taiwania cryptomerioidesin mountain areas of Taiwan. (A) Population (B) Community (C) Ecosystem (D) Behavioral (E) Landscape

27. Which of the following best describes directional selection? (A) Two or more phenotypes are common and drive diversity. (B) It occurs when one extreme phenotype has an advantage over all other phenotypes. (C) Larger individuals in a population have higher rates of survival than average and small individuals. (D) All of the above. (E) B and C are correct.

28. In a ___ distribution, many sample plots will contain few or no individuals while other plots will contain a large number. (A) clumped (B) regular (C) random (D) uniform (E) none of the above

29. Groups of plant or animal subpopulations which are spatially isolated but exchange individuals is called a (A) metapopulation. (B) community. (C) clumped distribution. (D) corridor. (E) none of the above.

30. Which of the following situations dose NOT increase species diversity in a community? (A) predation by keystone species. (B) habitat heterogeneity. (C) competitive exclusion. (D) moderate disturbances. (E) immigration of species.