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 producing heat-shock proteins, which may protect the plant's proteins from denaturing d. by increasing the proportion of unsaturated fatty acids in cell membranes, reducing their fluidity
Ch. 39 - Plant Responses to Internal and External Signals
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Campbell 11th Edition
Ch. 39 - Plant Responses to Internal and External Signals
Problem 7



Chapter 39, Problem 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 b. calcium c. statoliths d. differential growth

1
Identify the key terms in the question: The question mentions a plant mutant with normal gravitropic bending but no starch storage in plastids, and asks to reevaluate the role of a specific factor in gravitropism.
Understand gravitropism: Gravitropism is the orientation of a plant or other organism in response to gravity, where roots grow downward and stems grow upward.
Consider the role of statoliths: Statoliths are dense, starch-containing plastids that settle under the influence of gravity and help the plant detect the direction of gravity. This is crucial for normal gravitropic response.
Analyze the mutant's characteristics: Since the mutant shows normal gravitropic bending without starch storage, it suggests that starch might not be essential for gravitropism, challenging the traditional role assigned to statoliths.
Choose the correct answer: Given that the mutant can still perform gravitropism without starch, the role of statoliths (option c) in gravitropism needs to be reevaluated, as they might use another mechanism besides starch to function.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Gravitropism
Gravitropism is the growth response of plants to gravity, allowing them to orient their roots downward and stems upward. This process is crucial for plant stability and nutrient acquisition. It involves the perception of gravitational forces, which is mediated by specialized cells that detect gravity and signal the plant to grow accordingly.
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Statoliths
Statoliths are specialized organelles found in plant cells that play a key role in gravity sensing. These dense, starch-filled structures settle under the influence of gravity, helping the plant determine its orientation. The movement of statoliths within the cell influences the distribution of growth hormones like auxin, which in turn affects the direction of growth.
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Auxin
Auxin is a plant hormone that regulates various aspects of growth and development, including gravitropism. It promotes cell elongation on the side of the plant that is away from gravity, causing the plant to bend towards the gravitational pull. The interaction between auxin distribution and statoliths is essential for the plant's ability to respond to its orientation in space.
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Textbook Question
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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.
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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
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Textbook Question
DRAW IT Indicate the response to each condition by drawing a straight seedling or one with the triple response.
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