Textbook Question
Suppose that a mutant plant is unable to make methyl salicylate. Explain why it is not likely to survive in the wild.
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Ch. 37 - Plant Sensory Systems, Signals, and Responses
Chapter 37, Problem 11a
Leaflets of Mimosa pudica (common names: sensitive plant, touch-me-not) have a remarkable ability to close up in response to being touched or physically moved.
How fast can the leaflets close?
How does this occur?
And more importantly, what benefit could this unusual response provide to the plant?
Researchers studied the rate of closing and reopening of leaflets by measuring changes in the distance between opposing leaflets after being touched. Their results are shown in the accompanying graph (d/dmax is actual leaflet distance relative to maximal leaflet distance).
How long does it take for leaflets to close?
How long to reopen?
Verified step by step guidance1
Examine the graph provided in the problem, which shows the change in leaflet distance (d/dmax) over time after being touched.
Identify the point on the graph where the leaflets begin to close after being touched. This is typically marked by a rapid decrease in d/dmax.
Determine the time it takes for the leaflets to reach their minimum distance (fully closed position) by noting the time interval from the initial touch to the point where d/dmax is at its lowest.
Observe the graph for the reopening phase, which is indicated by an increase in d/dmax after reaching the minimum distance. Note the time it takes for the leaflets to return to their maximal distance (fully open position).
Consider the biological significance of this response. The rapid closing of leaflets may serve as a defense mechanism against herbivores or environmental stress, potentially deterring predators or minimizing damage.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Thigmonasty
Thigmonasty refers to the non-directional movement of plant parts in response to touch or physical stimuli. In Mimosa pudica, this rapid movement is facilitated by changes in turgor pressure within the pulvini, specialized cells at the base of the leaflets. When touched, these cells lose water, causing the leaflets to close quickly as a defense mechanism.
Turgor Pressure
Turgor pressure is the force exerted by fluid inside the cell against the cell wall, crucial for maintaining plant rigidity and facilitating movement. In Mimosa pudica, changes in turgor pressure within the pulvini cells lead to the rapid closing of leaflets. This pressure change is triggered by ion fluxes that cause water to move out of the cells, resulting in leaflet movement.
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Adaptive Significance
The closing of Mimosa pudica leaflets is thought to be an adaptive response to deter herbivores and protect the plant from harm. By closing quickly, the plant may appear less appealing or more difficult to consume, thus reducing the likelihood of being eaten. This response can also minimize water loss and protect against environmental stressors.
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Related Practice
Textbook Question
In general, small seeds that have few food reserves must be exposed to red light before they will germinate. (Lettuce is an example.) In contrast, large seeds that have substantial food reserves typically do not depend on red light as a stimulus to trigger germination. State a hypothesis to explain these observations.
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Textbook Question
In many species native to tropical wet forests, seeds do not undergo a period of dormancy. Instead, they germinate immediately. Predict the role of ABA in these seeds. How would you test your prediction?
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Textbook Question
Leaflets of Mimosa pudica (common names: sensitive plant, touch-me-not) have a remarkable ability to close up in response to being touched or physically moved.
How fast can the leaflets close?
How does this occur?
And more importantly, what benefit could this unusual response provide to the plant?
Which of the following terms best describes the leaflet movement?
a. Thigmonastic movements
b. Thigmotropism
c. Thigmomorphogenesis
d. Apical dominance
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Textbook Question
Leaflets of Mimosa pudica (common names: sensitive plant, touch-me-not) have a remarkable ability to close up in response to being touched or physically moved.
How fast can the leaflets close? How does this occur?
And more importantly, what benefit could this unusual response provide to the plant?
The mechanism of leaflet closure is similar to what happens during the shrinking of guard cells and closing of stomata (see Figure 37.22). When in the open position, special cells on the upper surface of Mimosa leaflets are filled with water and are under pressure.
Explain how osmosis and flow of ions into and out of these special cells may be involved in leaflet closure and reopening.
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Textbook Question
Leaflets of Mimosa pudica (common names: sensitive plant, touch-me-not) have a remarkable ability to close up in response to being touched or physically moved.
How fast can the leaflets close?
How does this occur?
And more importantly, what benefit could this unusual response provide to the plant?
If just the leaflets located toward the end of a leaf are touched, the adjacent leaflets close in fairly rapid succession until all leaflets on a leaf close up.
Explain how electrical signaling may be involved in this response.
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