Question
Plants respond to attacks by herbivores and pathogens
(pp. 845–847)
• In addition to physical defenses such as thorns and trichomes,
plants produce distasteful or toxic chemicals, as well as attractants
that recruit animals that destroy herbivores.
• The hypersensitive response seals off an infection and
destroys both pathogen and host cells in the region. Systemic
acquired resistance is a generalized defense response in
organs distant from the infection site.
How do chewing insects make plants more susceptible to pathogens?
TEST YOUR UNDERSTANDING
LEVEL 1: KNOWLEDGE/COMPREHENSION
1. The hormone that helps plants respond to drought is
a. auxin. d. ethylene.
b. gibberellin. e. abscisic acid.
c. cytokinin.
2. Auxin enhances cell elongation in all of these ways except
a. increased uptake of solutes.
b. gene activation.
c. acid-induced denaturation of cell wall proteins.
d. increased activity of plasma membrane proton pumps.
e. cell wall loosening.
3. Charles and Francis Darwin discovered that
a. auxin is responsible for phototropic curvature.
b. auxin can pass through agar.
c. light destroys auxin.
d. light is perceived by the tips of coleoptiles.
e. red light is most effective in shoot phototropism.
4. How may a plant respond to severe heat stress?
a. by reorienting leaves to increase evaporative cooling
b. by creating air tubes for ventilation
c. by initiating a systemic acquired resistance response
d. by increasing the proportion of unsaturated fatty acids in
cell membranes, reducing their fluidity
e. by producing heat-shock proteins, which may protect the
plant’s proteins from denaturing
LEVEL 2: APPLICATION/ANALYSIS
5. The signaling molecule for flowering might be released earlier
than usual in a long-day plant exposed to flashes of
a. far-red light during the night.
b. red light during the night.
c. red light followed by far-red light during the night.
d. far-red light during the day.
e. red light during the day.
6. If a long-day plant has a critical night length of 9 hours,
which 24-hour cycle would prevent flowering?
a. 16 hours light/8 hours dark
b. 14 hours light/10 hours dark
c. 15.5 hours light/8.5 hours dark
d. 4 hours light/8 hours dark/4 hours light/8 hours dark
e. 8 hours light/8 hours dark/light flash/8 hours dark
7. A plant mutant that shows normal gravitropic bending
but does not store starch in its plastids would require a
reevaluation of the role of ____________ in gravitropism.
a. auxin d. light
b. calcium e. differential growth
c. statoliths
?
8. Which type of mutant would be most likely to produce a
bushier phenotype?
a. auxin overproducer d. gibberellin overproducer
b. strigolactone overproducer e. strigolactone underproducer
c. cytokinin underproducer
9. Indicate the response to each condition by
drawing a straight seedling or one with the triple response.
DRAW IT
LEVEL 3: SYNTHESIS/EVALUATION
10. EVOLUTION CONNECTION
As a general rule, light-sensitive germination is more pronounced
in small seeds compared with large seeds. Suggest a reason why.
11. SCIENTIFIC INQUIRY
A plant biologist observed a peculiar pattern when a tropical
shrub was attacked by caterpillars. After a caterpillar ate a leaf,
it would skip over nearby leaves and attack a leaf some distance
away. Simply removing a leaf did not deter caterpillars
from eating nearby leaves. The biologist suspected that an
insect-damaged leaf sent out a chemical that signaled nearby
leaves. How could the researcher test this hypothesis?
12. SCIENCE, TECHNOLOGY, AND SOCIETY
Describe how our knowledge about the control systems of
plants is being applied to agriculture or horticulture.
13.
Environmental Interactions In a short essay
(100–150 words), summarize phytochrome’s role in altering
shoot growth for the enhancement of light capture.
For selected answers, see Appendix A.
WRITE ABOUT A THEME
1. MasteringBiology® Assignments
Experimental Inquiry Tutorial What Effect Does Auxin Have on
Coleoptile Growth?
Tutorial Plant Responses to Light
Activities Leaf Abscission • Flowering Lab • Plant Hormones •
Plant Defenses
Questions Student Misconceptions • Reading Quiz • Multiple
Choice • End-of-Chapter
2. eText
Read your book online, search, take notes, highlight text, and more.
3. The Study Area
Practice Tests • Cumulative Test • 3-D Animations •
MP3 Tutor Sessions • Videos • Activities • Investigations • Lab
Media • Audio Glossary • Word Study Tools • Art
(pp. 845–847)
• In addition to physical defenses such as thorns and trichomes,
plants produce distasteful or toxic chemicals, as well as attractants
that recruit animals that destroy herbivores.
• The hypersensitive response seals off an infection and
destroys both pathogen and host cells in the region. Systemic
acquired resistance is a generalized defense response in
organs distant from the infection site.
How do chewing insects make plants more susceptible to pathogens?
TEST YOUR UNDERSTANDING
LEVEL 1: KNOWLEDGE/COMPREHENSION
1. The hormone that helps plants respond to drought is
a. auxin. d. ethylene.
b. gibberellin. e. abscisic acid.
c. cytokinin.
2. Auxin enhances cell elongation in all of these ways except
a. increased uptake of solutes.
b. gene activation.
c. acid-induced denaturation of cell wall proteins.
d. increased activity of plasma membrane proton pumps.
e. cell wall loosening.
3. Charles and Francis Darwin discovered that
a. auxin is responsible for phototropic curvature.
b. auxin can pass through agar.
c. light destroys auxin.
d. light is perceived by the tips of coleoptiles.
e. red light is most effective in shoot phototropism.
4. How may a plant respond to severe heat stress?
a. by reorienting leaves to increase evaporative cooling
b. by creating air tubes for ventilation
c. by initiating a systemic acquired resistance response
d. by increasing the proportion of unsaturated fatty acids in
cell membranes, reducing their fluidity
e. by producing heat-shock proteins, which may protect the
plant’s proteins from denaturing
LEVEL 2: APPLICATION/ANALYSIS
5. The signaling molecule for flowering might be released earlier
than usual in a long-day plant exposed to flashes of
a. far-red light during the night.
b. red light during the night.
c. red light followed by far-red light during the night.
d. far-red light during the day.
e. red light during the day.
6. If a long-day plant has a critical night length of 9 hours,
which 24-hour cycle would prevent flowering?
a. 16 hours light/8 hours dark
b. 14 hours light/10 hours dark
c. 15.5 hours light/8.5 hours dark
d. 4 hours light/8 hours dark/4 hours light/8 hours dark
e. 8 hours light/8 hours dark/light flash/8 hours dark
7. A plant mutant that shows normal gravitropic bending
but does not store starch in its plastids would require a
reevaluation of the role of ____________ in gravitropism.
a. auxin d. light
b. calcium e. differential growth
c. statoliths
?
8. Which type of mutant would be most likely to produce a
bushier phenotype?
a. auxin overproducer d. gibberellin overproducer
b. strigolactone overproducer e. strigolactone underproducer
c. cytokinin underproducer
9. Indicate the response to each condition by
drawing a straight seedling or one with the triple response.
DRAW IT
LEVEL 3: SYNTHESIS/EVALUATION
10. EVOLUTION CONNECTION
As a general rule, light-sensitive germination is more pronounced
in small seeds compared with large seeds. Suggest a reason why.
11. SCIENTIFIC INQUIRY
A plant biologist observed a peculiar pattern when a tropical
shrub was attacked by caterpillars. After a caterpillar ate a leaf,
it would skip over nearby leaves and attack a leaf some distance
away. Simply removing a leaf did not deter caterpillars
from eating nearby leaves. The biologist suspected that an
insect-damaged leaf sent out a chemical that signaled nearby
leaves. How could the researcher test this hypothesis?
12. SCIENCE, TECHNOLOGY, AND SOCIETY
Describe how our knowledge about the control systems of
plants is being applied to agriculture or horticulture.
13.
Environmental Interactions In a short essay
(100–150 words), summarize phytochrome’s role in altering
shoot growth for the enhancement of light capture.
For selected answers, see Appendix A.
WRITE ABOUT A THEME
1. MasteringBiology® Assignments
Experimental Inquiry Tutorial What Effect Does Auxin Have on
Coleoptile Growth?
Tutorial Plant Responses to Light
Activities Leaf Abscission • Flowering Lab • Plant Hormones •
Plant Defenses
Questions Student Misconceptions • Reading Quiz • Multiple
Choice • End-of-Chapter
2. eText
Read your book online, search, take notes, highlight text, and more.
3. The Study Area
Practice Tests • Cumulative Test • 3-D Animations •
MP3 Tutor Sessions • Videos • Activities • Investigations • Lab
Media • Audio Glossary • Word Study Tools • Art
Answers
GPT-4o mini
### How Chewing Insects Make Plants More Susceptible to Pathogens
Chewing insects can significantly increase plants' susceptibility to pathogens through various mechanisms. When herbivores feed on plant tissues, they create wounds that serve as entry points for pathogens such as fungi, bacteria, and viruses. Additionally, the physical damage may disrupt the plant's defense mechanisms, allowing pathogens to establish infections more readily.
Moreover, the feeding activity of chewing insects can lead to the release of certain volatile organic compounds (VOCs) that can attract further herbivores or even exacerbate stress responses in the plant. This not only provides a nutrient-rich environment for pathogens but may also distract the plant's defenses, making it more difficult for the plant to mount an effective response against both the herbivores and the pathogens.
In sum, the mechanical damage caused by chewing insects, combined with the plant's altered physiological state and the associated chemical signals, can create favorable conditions for pathogen infection, leading to an increased vulnerability of the plant.
---
### Answer Key to Test Questions
1. e. abscisic acid.
2. c. acid-induced denaturation of cell wall proteins.
3. d. light is perceived by the tips of coleoptiles.
4. e. by producing heat-shock proteins, which may protect the plant’s proteins from denaturing.
5. c. red light followed by far-red light during the night.
6. e. 8 hours light/8 hours dark/light flash/8 hours dark.
7. c. statoliths.
8. b. strigolactone overproducer.
9. (For this question, illustrations of seedlings would be drawn based on the conditions given, which may include a straight seedling for normal growth or a seedling exhibiting the triple response under certain stress conditions.)
10. Light-sensitive germination is more pronounced in small seeds because they typically have limited energy reserves and require quick establishment in favorable environments. In contrast, larger seeds have greater stored energy, allowing them to germinate successfully without relying as heavily on light cues to indicate optimal growing conditions.
11. The researcher could conduct an experiment where they isolate leaves by cutting them off from the plant and applying extracts from the damaged leaves to adjacent leaves. They could then observe whether these treated leaves show any changes in herbivore attraction compared to control leaves. Additionally, using barriers to prevent physical herbivore access would help confirm if the chemical signals are the primary drivers of the observed behavior.
12. Our understanding of plant control systems has led to improved agricultural practices such as the development of genetically modified crops that exhibit enhanced stress resistance or increased yield. Techniques such as precision agriculture incorporate these insights to optimize water use and nutrient management, thereby improving crop health and productivity while minimizing environmental impacts.
13. Phytochrome plays a critical role in regulating shoot growth by allowing plants to detect light conditions in their environment. When phytochrome senses red light, it activates signaling pathways that promote stem elongation and leaf expansion, enabling the plant to optimize its growth for better light capture. In low light conditions or under competition, phytochrome signaling can trigger elongation responses, allowing the plant to grow taller and access more sunlight, which is essential for photosynthesis and overall plant health.
Chewing insects can significantly increase plants' susceptibility to pathogens through various mechanisms. When herbivores feed on plant tissues, they create wounds that serve as entry points for pathogens such as fungi, bacteria, and viruses. Additionally, the physical damage may disrupt the plant's defense mechanisms, allowing pathogens to establish infections more readily.
Moreover, the feeding activity of chewing insects can lead to the release of certain volatile organic compounds (VOCs) that can attract further herbivores or even exacerbate stress responses in the plant. This not only provides a nutrient-rich environment for pathogens but may also distract the plant's defenses, making it more difficult for the plant to mount an effective response against both the herbivores and the pathogens.
In sum, the mechanical damage caused by chewing insects, combined with the plant's altered physiological state and the associated chemical signals, can create favorable conditions for pathogen infection, leading to an increased vulnerability of the plant.
---
### Answer Key to Test Questions
1. e. abscisic acid.
2. c. acid-induced denaturation of cell wall proteins.
3. d. light is perceived by the tips of coleoptiles.
4. e. by producing heat-shock proteins, which may protect the plant’s proteins from denaturing.
5. c. red light followed by far-red light during the night.
6. e. 8 hours light/8 hours dark/light flash/8 hours dark.
7. c. statoliths.
8. b. strigolactone overproducer.
9. (For this question, illustrations of seedlings would be drawn based on the conditions given, which may include a straight seedling for normal growth or a seedling exhibiting the triple response under certain stress conditions.)
10. Light-sensitive germination is more pronounced in small seeds because they typically have limited energy reserves and require quick establishment in favorable environments. In contrast, larger seeds have greater stored energy, allowing them to germinate successfully without relying as heavily on light cues to indicate optimal growing conditions.
11. The researcher could conduct an experiment where they isolate leaves by cutting them off from the plant and applying extracts from the damaged leaves to adjacent leaves. They could then observe whether these treated leaves show any changes in herbivore attraction compared to control leaves. Additionally, using barriers to prevent physical herbivore access would help confirm if the chemical signals are the primary drivers of the observed behavior.
12. Our understanding of plant control systems has led to improved agricultural practices such as the development of genetically modified crops that exhibit enhanced stress resistance or increased yield. Techniques such as precision agriculture incorporate these insights to optimize water use and nutrient management, thereby improving crop health and productivity while minimizing environmental impacts.
13. Phytochrome plays a critical role in regulating shoot growth by allowing plants to detect light conditions in their environment. When phytochrome senses red light, it activates signaling pathways that promote stem elongation and leaf expansion, enabling the plant to optimize its growth for better light capture. In low light conditions or under competition, phytochrome signaling can trigger elongation responses, allowing the plant to grow taller and access more sunlight, which is essential for photosynthesis and overall plant health.