Q: Which equation best represents the acid growth hypothesis as it relates to auxin-induced cell elongation?

$$\text{Auxin} \rightarrow \text{Proton Pump Activation} \rightarrow \text{H}^+ \text{ secretion} \rightarrow \text{Cell Wall Acidification} \rightarrow \text{Expansin Activation} \rightarrow \text{Cell Elongation}$$

Question 1

Which of the following best describes the process of signal transduction in plant cells?

Accepted Answer

A stimulus is detected by a receptor, which initiates a cascade of events involving second messengers and protein kinases, ultimately leading to a cellular response.

Question 2

A plant is exposed to light on one side only. According to the acid growth hypothesis, what is the sequence of events that leads to the bending of the plant toward the light?

Accepted Answer

Auxin accumulates on the shaded side, stimulates proton pumps to lower pH, activates expansins, loosens the cell wall, and allows cells to elongate.

Question 3

Which hormone is primarily responsible for promoting seed dormancy and enhancing drought tolerance in plants?

Accepted Answer

Abscisic acid (ABA)

Question 4

A gardener removes the apical bud from a plant. What is the most likely outcome, and which hormones are involved in this process?

Accepted Answer

The plant becomes bushier due to the release of axillary buds, involving a decrease in auxin and an increase in cytokinin activity.

Question 5

Which of the following best explains why an overdose of synthetic auxin (such as 2,4-D) is used as a selective weed killer?

Accepted Answer

High concentrations of auxin disrupt normal growth processes in dicots, leading to their death, while monocots are less affected.

Question 6

A seedless grape variety is sprayed with gibberellins. What is the expected effect, and why?

Accepted Answer

The grapes will grow larger because gibberellins promote fruit growth and cell elongation.

Question 7

Which of the following scenarios best illustrates the role of ethylene in plants?

Accepted Answer

A batch of bananas ripens rapidly after one banana begins to ripen, due to ethylene gas stimulating fruit ripening in neighboring fruits.

Question 8

Which equation best represents the acid growth hypothesis as it relates to auxin-induced cell elongation?

Accepted Answer

$$	ext{Auxin} ightarrow 	ext{Proton Pump Activation} ightarrow 	ext{H}^+ 	ext{ secretion} ightarrow 	ext{Cell Wall Acidification} ightarrow 	ext{Expansin Activation} ightarrow 	ext{Cell Elongation}$$

Question 9

A mutant plant fails to undergo the triple response when exposed to ethylene. Which of the following is the most likely explanation?

Accepted Answer

The plant has a mutation in the ethylene receptor, preventing signal transduction.

Question 10

Which hormone is most directly involved in breaking seed dormancy and promoting germination, and what is its mechanism of action?

Accepted Answer

Gibberellin; it stimulates the synthesis of hydrolytic enzymes such as $$\alpha-$$amylase, which mobilize stored nutrients for the growing embryo.

Question 11

A plant is exposed to drought conditions. Which hormone is most likely to be produced in higher amounts, and what is its effect?

Accepted Answer

Abscisic acid (ABA); it promotes stomatal closure to reduce water loss.

Question 12

Which of the following best explains the phenomenon of apical dominance in plants?

Accepted Answer

High auxin levels produced by the apical bud suppress the growth of axillary buds.

Question 13

A plant is infected by a pathogen. Which of the following is a likely response involving plant hormones?

Accepted Answer

The plant increases ethylene production, which can lead to senescence and abscission of infected tissues.

Question 14

Which of the following best describes the interaction between auxin and cytokinin in tissue culture experiments?

Accepted Answer

High auxin to cytokinin ratio promotes root formation, while high cytokinin to auxin ratio promotes shoot formation.

Question 15

Which of the following is a real-world application of plant hormone knowledge in agriculture?

Accepted Answer

Spraying gibberellins on seedless grapes to increase fruit size.

Question 16

Which of the following best explains why leaves fall off trees in autumn?

Accepted Answer

A change in the balance of auxin and ethylene leads to the formation of an abscission layer, causing the leaf to detach.

Question 17

A plant is grown in complete darkness for a week and then exposed to light. What physiological changes would you expect to observe?

Accepted Answer

The plant will undergo de-etiolation, developing chlorophyll, expanding leaves, and strengthening its stem.

Question 18

Which of the following best describes the role of second messengers in plant signal transduction?

Accepted Answer

They transfer and amplify signals from receptors to proteins that cause cellular responses.

Question 19

A mutation in a plant prevents the activation of expansins. What is the most likely effect on the plant's growth?

Accepted Answer

The plant will have reduced cell elongation because the cell wall cannot be loosened.

Plant Signaling and Hormones: Mechanisms and Functions

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