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Ch. 39 - Plant Responses to Internal and External Signals
Campbell - Campbell Biology 11th Edition
Urry11th EditionCampbell BiologyISBN: 9789357423311Not the one you use?Change textbook
All textbooksUrry 11th EditionCh. 39 - Plant Responses to Internal and External SignalsProblem 8
Chapter 39, Problem 8

Indicate the response to each condition by drawing a straight seedling or one with the triple response.

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Understand the concept of the 'triple response' in plants, which is a growth pattern observed in seedlings when exposed to ethylene. This response includes inhibition of stem elongation, thickening of the stem, and horizontal growth.
Identify the conditions that lead to the triple response. Typically, this occurs when a seedling encounters an obstacle, such as soil or a rock, which triggers the production of ethylene.
Draw a straight seedling to represent normal growth conditions without the presence of ethylene. This seedling should have a long, thin stem growing vertically.
Draw a seedling exhibiting the triple response. This should include a short, thickened stem with a horizontal or curved growth pattern, indicating the presence of ethylene.
Label each drawing clearly to indicate which one represents normal growth and which one represents the triple response, ensuring that the differences in growth patterns are easily distinguishable.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Triple Response in Plants

The triple response in plants is a growth adaptation mechanism triggered by the plant hormone ethylene. It involves three key changes: inhibition of stem elongation, thickening of the stem, and horizontal growth. This response helps seedlings navigate through soil by altering their growth pattern to avoid obstacles.
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Ethylene Hormone

Ethylene is a gaseous plant hormone that regulates various aspects of growth and development, including fruit ripening, leaf abscission, and stress responses. In seedlings, ethylene is crucial for the triple response, allowing them to adapt their growth in response to environmental challenges.
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Seedling Growth Patterns

Seedling growth patterns refer to the ways in which young plants develop, typically characterized by vertical elongation towards light. However, under certain conditions, such as the presence of ethylene, seedlings may exhibit altered growth patterns like the triple response, which helps them overcome physical barriers in their environment.
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Related Practice
Textbook Question

A plant mutant that shows normal gravitropic bending but does not store starch in its plastids would require a reevaluation of the role of

a. Statoliths

b. Auxin

c. Calcium

d. Differential growth

Textbook Question

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

Textbook Question

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. 4 hours light/8 hours dark/4 hours light/8 hours dark

d. 8 hours light/8 hours dark/light flash/8 hours dark