1Chapter 28: External Factors and Plant GrowthMultiple-Choice Questions1. The Tropisms; p. 661; difficult; ans: eWhich of the following is NOT a finding from experiments on the role of auxin in phototropism of coleoptile tips?a. Light does not affect the total amount of auxin.b. Light does not destroy auxin.c. Auxin migrates from the lighted side to the shaded side.d. More auxin can be isolated from the shaded side of an intact tip than from the lighted side.e. If the tip is split and the two halves separated by a barrier, more auxin can be isolated from the shaded side than from the lighted side.2. The Tropisms; p. 661; moderate; ans: d______ light is the most effective in producing a phototropic response.a. Greenb. Yellowc. Oranged. Bluee. Red3. The Tropisms; p. 662; moderate; ans: aAccording to the original hypothesis on negative gravitropism of shoots, auxin is redistributed to the ______ side where it ______ cell expansion.a. lower; stimulates b. lower; inhibitsc. upper; stimulatesd. upper; inhibitse. upper; first inhibits then stimulates4. The Tropisms; p. 662; easy; ans: bIn roots and shoots, the statoliths are:a. chloroplasts.b. amyloplasts.c. plasma membranes.d. cell walls.e. lignified cells.5. The Tropisms; p. 662; moderate; ans: eIn roots, statoliths are localized in the:a. endodermis.b. vascular tissues.c. starch sheath.d. epidermis of the root cap.e. root cap columella.6. The Tropisms; p. 662; moderate; ans: aWhen a growing root is oriented horizontally, the amyloplasts in the central column of the rootcap:a. slide downward.b. float upward.c. attach to the nuclear envelope.d. attach to the mitochondria.e. do not move.7. The Tropisms; p. 663; moderate; ans: bIn the current model of root gravitropism, elongation is _____ in the upper side of the distal elongation zone and ______ along the lower side.a. stimulated; stimulated b. stimulated; suppressedc. suppressed; stimulatedd. suppressed; is neither stimulated nor suppressede. is neither stimulated nor suppressed; suppressed8. The Tropisms; p. 664; difficult; ans: eWhich of the following statements concerning hydrotropism is FALSE? a. It is the directed growth of roots in response to moisture.b. Decapped roots do not curve hydrotropically.c. Under normal gravity, hydrotropism is suppressed by gravitropism.d. Auxin apparently is required for hydrotropism.e. Inhibitors of auxin influx and efflux also inhibit hydrotropism. 9. The Tropisms; p. 665; moderate; ans: d Which of the following statements about thigmotropism is FALSE?a. It enables roots to navigate around rocks.b. It is a response to contact with a solid object.c. An example is the climbing of tendrils. d. Cells touching the support lengthen more than cells on the other side.e. The stems of peas can store the memory of tactile stimulation.10. Circadian Rhythms; p. 665; difficult; ans: aWhich of the following statements about circadian clocks is FALSE?a. Input pathways and output pathways are the parts of the clock that do not interact.b. Conceptually they consist of three parts.c. They cause the regular oscillation of 30-40 percent of Arabidopsis genes.d. The central oscillator is the part of the clock that generates rhythmic behavior.e. Input pathways are the part of the clock that carries information to the oscillator.11. Circadian Rhythms; pp. 666–667; difficult; ans: eIn terms of the circadian clock, gating refers to the observation that stimuli of _____ strength employed at different times of the day can result in ______ intensity of response.a. different; a smallerb. different; the samec. different; different d. equal; the samee. equal; a different12. Photoperiodism; p. 668; moderate; ans: aLong-day plants flower:a. in the summer.b. in early spring or fall.c. when exposed to eight hours of daylight.d. when the light period is shorter than a critical length.e. without respect to day length.13. Photoperiodism; pp. 668–669; difficult; ans: dWhich of the following statements concerning photoperiodism is FALSE?a. Short-day plants in the early spring or fall.b. Spinach and lettuce are examples of long-day plants.c. Day-neutral plants flower without respect to photoperiod.d. Photoperiodic behavior remains constant over a wide range of temperatures.e. In some plants, only a single exposure to the critical day-length will produce a response.14. Photoperiodism; p. 669; easy; ans: cExperiments on cocklebur have shown that the ______ perceives the photoperiod.a. apical meristemb. columellac. leaf bladed. petiolee. stem15. Photoperiodism; p. 670; moderate; ans: eIf a short-day plant receives a one-minute exposure to light in the middle of the dark period rather than continuous darkness, it will:a. produce more flowers.b. produce smaller flowers.c. produce larger flowers.d. flower at a lower temperature.e. not flower.16. Photoperiodism; p. 670; easy; ans: dLight with a wavelength of about ______ nanometers is the most effective for interrupting the dark period of both short-day and long-day plants.a. 220b. 340c. 440d. 660e. 730 17. Photoperiodism; p. 670; moderate; ans: dSuppose lettuce seeds are exposed to a series of alternating flashes of red light (abbreviated R) and far-red light (abbreviated FR). (E.g., a flash of red light followed by a flash of far-red light is denoted as R→RF.) Which of the following series of flashes would result in the germination of thoseseeds?a. FR onlyb. R→FRc. R→FR →R→FRd. R →FR→R→FR→Re. R→FR→R→FR→R→FR18. Photoperiodism; pp. 670-671; moderate; ans: cWhich of the following statements about Pr and Pfr is FALSE?a. They are photoreceptors.b. They participate in photoconversion reactions.c. Pr is the biologically active form.d. Pr absorbs 660-nanometer light.e. Pfr absorbs 730-nanometer light.19. Photoperiodism; p. 671; easy; ans: bWhen lettuce seeds are exposed to red light:a. Pfr is converted to Pr.b. Pr is converted to Pfr.c. 660-nanometer light is converted to 730-nanometer light.d. 730-nanometer light is converted to 660-nanometer light.e. they will not germinate.20. Photoperiodism; p. 671; moderate; ans: a Which of the following statements concerning the phytochrome molecule is FALSE?a. The phytochromes in Arabidopsis are encoded by just 2 genes.b. Most plants have several different phytochromes. c. The chromophore portion is similar to the phycobilins in cyanobacteria.d. One part is a protein.e. The chromophore portion absorbs light.21. Photoperiodism; p. 672; moderate; ans: dWhen phytochromes interact