18. Which of the following best describes double fertilization in flowering plants?
(A) Flowers must be pollinated twice to yield both fruits and seeds.
(B) One sperm fertilizes the egg, and a second sperm fertilizes both polar nuclei.
(C) The egg of the embryo sac is diploid.
(D) Two sperms are needed to fertilize the egg.

14. Under what conditions do photosynthesis and cellular respiration occur in plants? (A) Photosynthesis and cellular respiration occur oniy in the light (B) Photosynthesis occurs only in the light, and cellular respiration occurs only in the dark. (C) Photosynthesis occurs only in the light, and cellular respiration occurs in both the dark and the light. (D) Photosynthesis and cellular respiration occur in both the light and the dark.

15. What would be the expected effect on C3 and C4 plants if the atmospheric CO2 concentration was doubled? (A) All plants would have faster growth rates. (B) C3 plants would have faster growth rates； C4 plants would be minimally affected. (C) C4 plants would have faster growth rates； C3 plants would be minimally affected. (D) C3 plants would have faster growth rates； C4 plants would have slower growth rates.

16. Aquaporins _______ . (A) allow water to cross the plasma membrane along its concentration gradient (B) allow water to cross the plasma membrane against its concentration gradient (C) allow for the active transport of water (D) are found in all cells

17. Which of the following are the male gametophytes in flowering plants? (A) stamens (B) shoot parts bearing male flowers (C) pollen grains (D) anthers

19. The following steps occur during a plant's response to drought stress.I) ABA accumulates in the leaves II) stomata closeIII) transpiration decreasesIV) guard cell potassium channels openWhich of the following places the steps in the correct sequence to represent the acquisition of droughttolerance in the plant?(A) I, II. Ill, and IV (B) I, IV, II, and 111 (C) II, I, III. and IV (D) IV, I, II, and III

20. Which of the following events is most immediately associated with the absorption of energy by chlorophyll molecules of the reaction-center complex? (A) ATP is synthesized from the energy absorbed. (B) A molecule of water is split. (C) An electron is excited. (D) NADP+ is reduced to NADPH.

21. The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following? (A) A gene from an organism can theoretically be expressed by any other organism. (B) AII organisms have experienced convergent evolution. (C) DNA was the first genetic material. (D) The same codons in different organisms translate into different amino acids.

22. E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment? (A) one high-density and one low-density band (B) one intermediate-density band (C) one intermediate-density and one low-density band (D) one low-density band

23. Put the following steps of DNA replication in the proper order. 1. Single-stranded binding proteins attach to DNA strands. 2. Hydrogen bonds between base pairs of antiparallel strands are broken. 3. Primase binds to the site of origin. 4. DNA polymerase binds to the template strand. 5. An RNA primer is created.(A)2, 3, 5,1,4 (B)2,1,3,5,4 (C)3, 2, 1,5,4 (D)3, 1,2, 5,4

24. You want to engineer a eukaryotic gene into a bacterial colony and have it expressed. What must be included in addition to the coding exons of the gene? (A) eukaryotic polymerases (B) a bacterial promoter sequence (C) a eukaryotic promoter sequence (D) bacterial ligases