Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 36
Test Yourself Questions
1. What kinds of molecules move within plants from one place to another, influencing plant development
and behavior?
a. plant hormones and RNA molecules such as microRNAs (miRNAs)
b. secondary messengers
c. effectors
d. receptors
e. none of the above
Answer: a. Plant hormones and RNA molecules move within plants, thereby influencing plant
development and behavior.
2. Phototropism is
a. the production of flowers in response to a particular day length.
b. the production of flowers in response to a particular night length.
c. the growth response of a plant, organ system, or organ to directional light.
d. illustrated by sun tracking.
e. none of the above.
Answer: c. Photoperiodism is the growth response of a plant or plant part to directional light.
3. What is the most accurate order of events during signal transduction?
a. first, receptor activation, then messenger signaling, and last, an effector response
b. first, an effector response, then messenger signaling, and last, receptor activation
c. first, messenger signaling, then receptor activation, and last, an effector response
d. first, an effector response, then receptor activation, and last, messenger signaling
e. none of the above
Answer: a. First a receptor is activated, then messenger signaling usually occurs, and finally, an effector
causes a response.
4. Which of the plant hormones is known as the “master hormone”?
a. cytokinin
b. gibberellin
c. abscisic acid
d. brassinolide
e. none of the above
Answer: e. None of the above; auxin is considered to be the master plant hormone.
5. Which of the major plant hormones is a diffusible gas?
a. auxin
b. gibberellin
c. cytokinin
d. ethylene
e. abscisic acid
Answer: d. Ethylene is a diffusible, gaseous hormone. NO, which is not considered a major plant
hormone, is also a gas.
6. Which of these molecules is considered to be a plant photoreceptor?
a. cryptochrome
b. phototropin
c. phytochrome
d. all of the above
e. none of the above
Answer: d. Cryptochrome, phototropin, and phytochrome are all plant photoreceptors.
7. Thigmotropism is a plant response to
a. light.
b. cold.
c. touch.
d. gravity.
e. drought.
Answer: c. Thigmotropism is plant response to touch.
8. Which response is an adaptation to flooding?
a. production of heat shock proteins
b. stomatal closure
c. vernalization
d. production of aerenchyma
e. all of the above
Answer: d. The production of aerenchyma, tissue with air channels, which is mediated by ethylene, is an
adaptive response to flooding.
9. What are avirulence genes?
a. plant genes that encode proteins that prevent infection (virulence)
b. plant genes that cause infection when the proteins they encode bind to pathogen elicitors
c. pathogen genes that prevent the pathogens from causing plant disease
d. pathogen genes that encode elicitors that foster disease in plants
e. none of the above
Answer: d. Avirulence genes, despite their name, encode elicitors that cause plant disease.
10. How do plants defend themselves against pathogens?
a. Plants produce resistance molecules (usually proteins) that bind pathogen elictors, thereby
preventing disease.
b. Plants display a hypersensitive response that limits the ability of pathogens to survive and
spread.
c. Plants display systemic acquired resistance, whereby an infection induces immunity to
diverse pathogens in other parts of a plant.
d. All of the above are correct.
e. None of the above is correct.
Answer: d. Plants defend themselves by means of resistance molecules, the hypersensitive response,
and systemic acquired resistance.
Conceptual Questions
1. Why can plants be said to display behavior?
Answer: Behavior is defined as response to a stimulus. Therefore, because plants display many kinds of
responses to diverse stimuli, they display behavior.
2. Why do plants produce so many types of resistance (R) genes?
Answer: Many kinds of disease-causing bacteria and fungi occur in nature, and these organisms evolve
very quickly, producing diverse elicitors. Thus, plants must maintain a stock of resistance genes, each
having many alleles.
3. Because diverse plants exude volatile compounds in response to herbivore or pathogen attack, some
experts have written about “talking trees.” Is there any such thing?
Answer: Talking implies a conversation with “listeners” who detect a message and respond to it. Thus,
plants that exude volatile compounds that attract enemies of herbivores could be interpreted as “talking”
to those enemies. The message is “Hey, you guys, there’s food for you over here.” In addition, research
has revealed that some plants near those under attack respond to volatile compounds by building up
defenses. “Talking” to other plants does not enhance the “talker’s” fitness. But the ability to “listen”
enhances the “listener’s” fitness, because it can take preemptive actions to prevent attack.
Experimental Questions
1. Boysen-Jensen used gelatin to collect diffusible auxin from shoot tips, but Went switched to agar, and
Briggs followed suit. Why is agar better for this purpose than gelatin?
Answer: Agar is more resistant to breakdown resulting from microbial attack or heat than is gelatin, and
thus is more stable during experiments.
2. How did Briggs determine that light does not destroy auxin?
Answer: He compared the degree to which shoots bent whose tips had been replaced by blocks
containing agar collected from tips exposed to light or not. If light destroys auxin, then the agar blocks
that collected auxin from light-treated shoots should have caused less bending than did blocks from
darkened tips. But the experimental shoots bent to the same degree—Briggs thus falsified the
hypothesis that light destroys auxin.
3. What is the current hypothesized mechanism by which auxin accumulation causes shoot bending in
response to directional light?
Answer: Hypothetically, auxin enhances the rate at which cell membrane proton pumps acidify the plant
cell wall, thereby allowing cells to extend. Although the evidence for acid effects on cell wall extension is
strong, the molecular basis of possible auxin effects on proton pumps is not as yet clear.
Collaborative Questions
1. Why are most wild plants distasteful, and some even poisonous, to people?
Answer: Natural plants produce bad-tasting secondary metabolites that keep herbivores from
completely destroying them. Humans have taste receptors similar to those of other animals. Thus, the
defensive chemicals taste bad to us also.
2. How could you increase the resistance of a particular crop plant species to particular types of
herbivores?
Answer: You could try to identify secondary metabolites that are distasteful to the particular herbivores,
and yet not distasteful or toxic to humans. If such compounds can be identified, you could determine
which pathway enzymes for synthesizing these metabolites are missing from the crop plant or
expressed at too low a level. You could try to use genetic engineering or conventional breeding
techniques to add the missing enzymes to the crop genome, or increase the levels of metabolite
expression. Alternatively, you could try to modify the crop so that it exudes volatile compounds that
attract the enemies of the herbivores.