20. Flowers of night-blooming cereus are open at night and closed during the day. This is an example of a:
(A)positive phototropic response.
(B) negative phototropic response.
(C)photonastic response.
(D)photomorphogenic response.
(E)positive phototaxis response.

16. Which of the following about phloem translocation is false? (A)It is explained by pressure flow hypothesis. (B) At sources, sugars are actively transported to sieve elements. (C)Water moves out from sieve elements at sources. (D)At sinks, sugars are actively transported from sieve elements to sink cells.

17. Which of the following statements is true? (A)The contents of the phloem are under pressure and the contents of the xylem are under tension. (B) Sieve tube members are empty, dead cells. (C)Vessel element protoplasm is unique because the vacuolar membrane disintegrates, allowing vacuolar water to mix with the cytosol. (D)Phloem sap movement is driven by the atmospheric water potential. (E)Phloem sap moves only short distances, whereas xylem sap moves long distances.

18. Which of the following is false about criteria for essentiality for a mineral? (A)The element must be necessary for complete plant development in its entire life cycle. (B) The element cannot be substituted to be effective and must be necessary by itself. (C)The element can be substituted to be effective. (D)The element must be acting inside the plant and not outside of it.

19. Essential elements would not be made available to plants by: (A)alternate freezing and thawing of rock. (B) runoff from rainstorms and avalanches. (C)acids released by an organism called a lichen. (D)the release of CO2 by roots. (E)being incorporated into the crystalline matrix of rocks.

21. Which of the following was the first plant hormone discovered? (A)Gibberellin (B) Auxin (C)Abscisic acid (D)Ethylene (E)Cytokinin

22. If plants are kept in the dark, they have elongated internodes, making them spindly. This effect is due to: (A)an overproduction of auxin. (B) phytochrome in the Pr form. (C)phytochrome in the Pfr form. (D)an overproduction of gibberellins. (E)a lower auxin/cytokinin ratio in the stems.

23. What do results of research on gravitropic responses of roots and stems show? (A)The effect of a plant hormone can depend on the tissue. (B) Different tissues have the same response to auxin. (C)Some responses of plants require no hormones at all. (D)Cytokinin can only function in the presence of auxin.

24. The most recently evolved group of plants are the: (A)ferns. (B) conifers. (C)gnetophytes. (D)flowering plants. (E)cycads.

25. The habitat of a plant species would include all of the following except: (A)a person who picks some of the species' flowers once. (B) nearby plants of other species. (C)the composition of the soil. (D)insects that lay their eggs in the plant's leaves. (E)length of the growing season.

26. Fossil material of progymnosperms, a now extinct group, never contains: (A)megaphylls. (B) two kinds of spores.(C)seeds. (D)secondary xylem and phloem. (E)cork cambia.