37. Plant Sensation and Response

Tropisms and Hormones

Mechanisms of Plant Growth

 No. Stem thickening is part of the triple response. 

 No. During the triple response, asymmetric growth results in stem curvature. 

 No. The triple response results in the inactivation of kinase. This allows synthesis of the proteins required for the triple response. 

 No. The triple response is promoted by ethylene. 

How does ethylene affect growth? .

The triple response to mechanical stress results in __________.

 No. Gibberellins and auxin are responsible for cell elongation. 

 No. As an inhibitor of both primary and secondary growth, abscisic acid may play a role in the onset of dormancy. 

 No. Strigolactones help establish mycorrhizal associations. 

Review the functions of plant hormones. .

A graduate student growing plant cells in a laboratory dish wants them to __________; therefore, the student treats them with cytokinins.

Thigmotropism and Cytokinins

Animation:  Water-Soluble Hormone Pathway

Short Video: Prokaryotic Flagella

Plant Senescence II: Signals Affecting Senescence

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.

Tropism (Types, positive & negative) | Control & Coordination | Biology | Khan Academy

Animation: Reproductive Cycles of the Human Female

 No. The opposite is the correct answer. 

 No. Gibberellins stimulate growth in length but do not by themselves inhibit branching. Ethylene may be a growth inhibitor. 

 No. Gibberellins stimulate growth in length but do not by themselves inhibit branching. Abscisic acid inhibits plant growth. 

 No. Auxin is the correct choice. Abscisic acid, however, inhibits plant growth. 

The interaction of various hormones results in specific responses in the plant.

In shoots, branching is inhibited by __________ from the tip of a growing shoot, but this effect is countered by __________ from the roots.

 No. Abscisic acid is an inhibitor of plant growth. 

 No. Cytokinins stimulate lateral branching. 

 No. Ethylene is an inhibitor of cell elongation. 

 No. Brassinosteroids induce cell elongation and division in stem segments and seedlings. The effects of brassinosteroids are quite similar to the effects of auxin. 

Consider the hormone responsible for "foolish seedling disease."

As leaf lettuce matures, a tall flowering shoot extends beyond the basal, edible leaves. After the plant bolts like this, it no longer produces broad, tasty leaves. Suppose you want to prevent bolting so that you can harvest lettuce longer. You may want to prevent the plant from synthesizing __________.

 No. Heat-shock proteins do not promote water loss. 

 They regulate stomatal opening and closing. 

 No. This is not the function of heat-shock proteins. 

 No. This is not how heat-shock proteins work. 

 No. Water potential can be affected by the production of organic compounds retained within the cell. 

 They help other proteins retain their functional shapes. 

Consider the mechanisms by which excessive heat exerts its effects.

How are heat-shock proteins thought to work?

Animation: Binding of Hormones

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

Plant Hormones and Senescence

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 have hypothesized that rapid leaf movements in Mimosa serve as a defense mechanism (e.g., closing leaflets may deter plant-eating insects). Propose an experiment to test this hypothesis.

 No. Gibberellins do not help establish mycorrhizal associations. 

 No. Brassinosteroids do not help establish mycorrhizal associations.  

 No. Although cytokinins do interact with auxin in the modification of apical dominance, they do not participate in the establishment of mycorrhizal associations. 

 None of the listed responses is correct. 

 No. One of the choices is a correct answer. 

In addition to interacting with auxin in the control of apical dominance, newly discovered plant hormones help to establish mycorrhizal associations by attracting mycorrhizal fungi to the plant roots. What are these hormones called?

Plant Senescence Basics

 No. Water deficits stimulate an increased synthesis and release of abscisic acid from mesophyll cells, which keeps stomata closed by acting on guard cell membranes. 

 No. A response to oxygen deprivation in waterlogged soils is the formation of air tubes that provide oxygen to submerged roots. 

 No. The closing of stomata and the production of heat-shock proteins are responses to heat stress. 

 No. Some plants respond to herbivory by producing compounds that deter herbivores by a variety of means. 

How might the tonicity be equalized? .

The production of organic solutes by plants is a response to __________.

Short Video: Gravitropism

Cytokinins

Plant Hormones - Tropisms & Auxins  #52

The hormone that helps plants respond to drought is
a. auxin.
b. abscisic acid.
c. cytokinin.
d. ethylene.

PLANT HORMONES - Auxin Gibberellin Cytokinin Ethylene Abscisic Acid

Plant Responses to the Environment: Tropisms and Defenses

Negative Gravitropism | Demonstration

 increase the hydrostatic pressure in cells, stretching their walls 

 No. Although the increased uptake of water does occur, another of the choices is a more immediate and direct effect of auxin. 

 shift the pH and thus activate enzymes that break the hydrogen bonds 

 No. Although the acidification of the cell wall activates expansins that break hydrogen bonds, another of the choices describes a more immediate and direct effect of auxin. 

 No. Although ion uptake by the cell increases the movement of water into the cell, another of the choices describes a more immediate and direct effect of auxin. 

 activate the synthesis of new cytoplasm 

 No. The synthesis of cytoplasm occurs after the initial elongation. 

activate ATP-driven proton (H+) pumps

This mechanism is based on ion transport. .

The immediate, direct effect of auxin in cell elongation, according to the acid growth hypothesis, is to __________.

Plant Tropism

Short Video: Mimosa Leaf

 No. Gravitropism is movement in response to gravity. This is an example of a tropism, but there is a better response. 

 No. Phototropism is movement in response to light. This is an example of a tropism, but there is a better response. 

 No. Thigmotropism is movement in response to touch. This is an example of a tropism, but there is a better response. 

 No. Heliotropism is movement in response to solar position. This is an example of a tropism, but there is a better response. 

 All of the listed responses are correct. 

Consider the meanings of the suffixes and prefixes of the choices.

What is growth that results in curvatures of whole plant organs toward or away from stimuli called?

 No. Phytoalexins are antimicrobial compounds produced in response to infection. 

 No. Gibberellins stimulate plant growth but not plant orientation. 

 No. Cytokinins stimulate plant growth but not plant orientation. 

 No. Phytochromes play a role in a plant's response to light and photoperiod. 

A type of plastid is involved in the response to gravity.

__________ appear to allow a plant cell to sense its orientation with respect to gravity.

Plant Growth Regulators: What are Plant Hormones [Horticulture 101 Series]

Animation: Steroid Hormone Pathway

 No. A plant in salty water is in a hypertonic solution. 

 No. The formation of air tubes is a response to the oxygen deprivation that occurs when roots are submerged. 

 No. This is a response to a deficit of water. 

Consider the effects on tonicity and water potential of increased soil salinity. .

When a plant that is not adapted to salty water is exposed to salty water, it will __________.

 No. Equal concentrations of auxin and cytokinin allow the cells of the callus to increase in number, but the cells remain undifferentiated. 

 No. A low concentration of auxin relative to cytokinin would stimulate the development of shoot buds from the callus. 

 No. Different ratios of the two hormones have different effects on the callus. 

The interaction of the two hormones results in specific responses. .

A callus will develop roots if you use a __________ auxin concentration and a __________ cytokinin concentration in the medium.

 No. A florist would most likely use a cytokinin spray because cytokinins slow aging and deterioration. 

Which hormone would a florist most likely spray on cut flowers to keep them fresh?

 No. These are the correct hormones, but it is a decrease in auxin that results in changes in the abscission layer. 

 No. Neither of these hormones plays a role in leaf abscission. 

 No. Only one of these hormones plays a role in leaf abscission. 

The ratio of which two hormones affects the interface between the stem and petiole? .

In the autumn, the amount of __________ decreases, rendering the cells of the abscission layer more sensitive to __________.

 No. The germination of seeds requires an uptake of water by the seeds. 

 No. Such a response involves either the inhibition or stimulation of cell elongation. Cell elongation involves enzymes loosening the cell wall. 

 stomatal opening, initiating photosynthesis 

 No. The loss of water from guard cells would result in the closure of stomata. 

 stress that results in the production of PR proteins 

 No. PR proteins are produced in response to infection. 

Consider this question in terms of how the loss of water affects plant cells that are placed in a hypertonic solution.

A rapid loss of water in specialized cells in the sensitive plant Mimosa pudica causes __________.

 No. The production of organic solutes by plants is a response to salt stress. 

How would additional unsaturated fatty acids in the cell membrane affect the membrane's fluidity? .

Increasing the proportion of unsaturated fatty acids in their membranes is a response of plants to __________.

thigmotropism

 No. Roots submerged in water are not suffering from a water deficit. 

 No. Some plants respond to cold stress by changing the solute composition of their cells. 

Consider what air tubes would bring to submerged roots.

The formation of air tubes in submerged roots is an adaptation to __________.

 No. This is true, but there is a better answer. Ethylene is an organic compound. 

 No. This is true, but there is a better answer. 

 Ethylene is involved in one of the rare examples of a positive feedback loop. 

 No. This is true, but there is a better answer. Consider the relationship between ethylene and ripening.  

 A burst of ethylene is almost always associated with apoptosis. 

Which of these features is/are characteristic of ethylene?

BioFlix: Mechanism of Hormone Action: Second Messenger cAMP

 No. A response to oxygen deprivation in waterlogged soil is the formation of air tubes that provide oxygen to submerged roots. 

 No. Some plants respond to herbivory by producing chemicals that attract predators of those herbivores. 

Think about the relationship between solute concentration and the movement of water across the cell membrane. .

Increasing the cytoplasmic levels of specific well-tolerated solutes, such as sugars, helps a plant to cope with __________.

 No. Hormones regulate the bending of a plant toward light. 

 No. Cytokinins are produced in actively growing tissues, such as roots, embryos, and fruits. 

 is the location of the biological clock in a plant 

 No. The biological clock has not been localized to such a specific region. 

 detects light and measures the photoperiod 

 No. This function is performed by phytochromes. 

How does the ratio of ethylene to auxin affect the interface between the stem and petiole? .

The abscission layer __________.

 No. Phytochromes play a role in photoperiodism. 

 No. Gibberellins stimulate stem elongation. 

 No. Phytoalexins are antimicrobial compounds produced by plants in response to infection. 

This hormone also plays a major role in a plant's response to drought.

Seeds of many desert plants will not germinate until a heavy rain washes away their __________.

Plant Growth Regulators

Animation: Hormonal Control of the Testes

Abscisic acid is involved in seed dormancy.

The synthesis and release of abscisic acid in a plant is a response to __________.

Gravitropism

 No. This statement is true, but there is a better response. 

 No. This response to water deficit occurs even if heat is not the cause of the water deficit. 

 Production of heat-shock proteins, closing of stomata, and altering the lipid composition of their membranes 

 No. The third part of this choice describes a plant's response to cold stress. 

 Production of heat-shock proteins and closing of stomata 

Consider the consequences of high temperatures.

Which of the following describes a plant's response to heat stress?

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