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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
note: provide full questions with the answers

1 answer

Here are the questions along with their respective answers:

TEST YOUR UNDERSTANDING

LEVEL 1: KNOWLEDGE/COMPREHENSION

  1. The hormone that helps plants respond to drought is
    e. abscisic acid.

  2. Auxin enhances cell elongation in all of these ways except
    a. increased uptake of solutes.

  3. Charles and Francis Darwin discovered that
    d. light is perceived by the tips of coleoptiles.

  4. How may a plant respond to severe heat stress?
    e. by producing heat-shock proteins, which may protect the plant’s proteins from denaturing.

LEVEL 2: APPLICATION/ANALYSIS

  1. The signaling molecule for flowering might be released earlier than usual in a long-day plant exposed to flashes of
    c. red light followed by far-red light during the night.

  2. If a long-day plant has a critical night length of 9 hours, which 24-hour cycle would prevent flowering?
    e. 8 hours light/8 hours dark/light flash/8 hours dark.

  3. 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.
    c. statoliths.

  4. Which type of mutant would be most likely to produce a bushier phenotype?
    e. strigolactone underproducer.

  5. Indicate the response to each condition by drawing a straight seedling or one with the triple response.
    (This question requires visual representation and cannot be answered textually.)

LEVEL 3: SYNTHESIS/EVALUATION

  1. EVOLUTION CONNECTION
    As a general rule, light-sensitive germination is more pronounced in small seeds compared with large seeds. One reason for this is that small seeds typically have limited energy reserves and must germinate quickly when conditions are favorable. Light signals indicate that the surface environment is suitable for growth, therefore quick germination in response to light increases the chances of survival and successful establishment in competitive environments.

  2. SCIENTIFIC INQUIRY
    To test the hypothesis that an insect-damaged leaf sends out a chemical signal to nearby leaves, the researcher could conduct an experiment. They could use plants that have had their leaves damaged by caterpillars and then isolate portions of the plant to determine if any chemical is released. The researcher could treat some nearby undamaged leaves with these chemicals and observe if they show similar susceptibility to caterpillars or whether they experience changes in defenses. Alternatively, the researcher could use a control group of undamaged leaves that do not receive exposure to the chemicals to assess differences in caterpillar feeding behavior.

  3. SCIENCE, TECHNOLOGY, AND SOCIETY
    Our knowledge about the control systems of plants is significantly impacting agriculture and horticulture. For example, understanding plant hormones allows for the development of synthetic growth regulators that enhance fruit ripening, improve stress responses, or regulate flowering times to increase yield. Additionally, knowledge of pest resistance mechanisms in plants supports the breeding of crops that are more resilient to herbivores and pathogens, thus reducing the need for chemical pesticides and making agriculture more sustainable.

  4. Environmental Interactions
    Phytochrome is a photoreceptor that allows plants to detect light quality, quantity, and direction, which is essential for optimizing shoot growth. Upon exposure to red light, phytochrome undergoes a conformational change, activating signal transduction pathways that promote stem elongation. This response allows plants to grow towards the light source, maximizing light capture for photosynthesis. In contrast, under far-red light, phytochrome reverts to its inactive form, leading to reduced growth in shaded conditions. By adjusting their growth in response to light conditions, plants enhance their competitive ability in diverse environments.

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