37. Plant Sensation and Response

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

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

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?

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

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

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

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

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 __________.

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

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

How are heat-shock proteins thought to work?

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

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

The triple response to mechanical stress results in __________.

The abscission layer __________.

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

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

Which of these features is/are characteristic of ethylene?

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

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

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

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

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

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

Test your knowledge of the five major classes of plant hormones (auxins, cytokinins, gibberellins, abscisic acid, ethylene) by matching one hormone to each lettered box. (Note that some hormones will match up to more than one box.)

What does reverse transcriptase do?

During winter or periods of drought, which one of the following plant hormones inhibits growth and seed germination? a. ethylene b. abscisic acid c. gibberellin d. auxin

Which of the following statements about hormones is correct? a. They tend to be large molecules. b. They exert their effects only on the same cells that produce them. c. They can exert strong effects only when they are present in high concentrations. d. They trigger a response by binding to target-cell receptors.

In autumn, the amount of _________ increases and the amount of _________ decreases in fruits and leaf stalks, causing a plant to drop fruit and leaves. a. ethylene … auxin b. gibberellin … abscisic acid c. cytokinin … abscisic acid d. auxin … ethylene

What evidence suggests that ABA from roots can signal guard cells to close? a. If roots are given sufficient water, guard cells close anyway. b. If roots are dry, guard cells begin to close—even though leaves may not be experiencing water stress. c. Applying ABA on guard cells directly causes them to close. d. If roots are dry, the ABA concentration in leaf cells drops dramatically.

Plant hormones act by affecting the activities of a. genes. b. membranes. c. enzymes. d. genes, membranes, and enzymes.

Why was it logical to predict that amyloplasts function as statoliths? a. They are dense and settle to the bottom of gravity-sensing cells. b. They are present only in gravity-sensing cells. c. They make a direct physical connection with membrane proteins that have been shown to be gravity-receptor molecules. d. Their density changes in response to gravity.

Buds and sprouts often form on tree stumps. Which hormone would stimulate their formation? a. auxin b. cytokinin c. abscisic acid d. ethylene

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

To explore how hormones function, researchers have begun to transform plants with particular genes. In one experiment, a gene involved in cytokinin synthesis was introduced into tobacco plants. Which one of the following results would be expected? a. Individuals produced more lateral branches. b. Stems grew extremely tall and slender. c. Roots were incapable of responding to gravity. d. Stomata were closed most of the time.

"Match each definition with the correct term. Bending of a shoot toward light Growth response to touch Cycle with a period of about 24 hours Pigment that helps control flowering Relative lengths of night and day Growth response to gravity Folding of plant leaves at night a. phytochrome b. photoperiod c. sleep movement d. circadian rhythm e. thigmotropism f. phototropism g. gravitropism"

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

Which of the following types of viruses would you expect to require periods of latency? a. viruses that have large genomes and require a long time for replication b viruses that require a long time for transmission to new hosts c viruses that require a long time for assembly into complex structures d. viruses that infect cells of the immune system

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?

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?

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

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.

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.

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.

If apples are to be stored for long periods, it is best to keep them in a place with good air circulation. Explain why.

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? Mimosa leaflets also close on their own at dusk and reopen at dawn (this cycle develops as a circadian rhythm). What receptor molecule mentioned in this chapter is likely involved in regulating this process?

Write a short paragraph explaining why a houseplant becomes bushier if you pinch off its terminal buds.