Q: What is the acid growth hypothesis, and which equation best represents the process of cell wall acidification?

Auxin activates proton pumps, increasing $$\text{H}^+$$ concentration in the cell wall: $$\text{ATP} + \text{H}^+ \rightarrow \text{Acidified Cell Wall}$$

Question 1

Which plant hormone is primarily responsible for promoting cell elongation in the shoot, and what mechanism does it use to achieve this effect?

Accepted Answer

Auxin; by activating proton pumps that lower cell wall pH and activate expansins

Question 2

A plant is exposed to drought conditions. Which hormone is most likely to accumulate and what is its primary effect?

Accepted Answer

Abscisic acid (ABA); causes stomata to close rapidly

Question 3

A scientist applies gibberellins to a rosette-form plant. What change would you expect to observe?

Accepted Answer

The plant will undergo bolting, resulting in rapid elongation of the floral stalk.

Question 4

Which combination of hormones is required for fruit development in many plants, such as grapes?

Accepted Answer

Auxin and gibberellins

Question 5

What is the acid growth hypothesis, and which equation best represents the process of cell wall acidification?

Accepted Answer

Auxin activates proton pumps, increasing $$	ext{H}^+$$ concentration in the cell wall: $$	ext{ATP} + 	ext{H}^+ ightarrow 	ext{Acidified Cell Wall}$$

Question 6

A seed remains dormant until exposed to heavy rain, light, or prolonged cold. Which hormone is most likely responsible for maintaining dormancy, and what happens when its levels decrease?

Accepted Answer

Abscisic acid (ABA); dormancy is broken and the seed germinates

Question 7

Which hormone is most likely to be used by fruit producers to control the timing of fruit ripening, and what is the underlying mechanism?

Accepted Answer

Ethylene; by triggering ripening and positive feedback production of more ethylene

Question 8

A plant bends toward a light source. Which hormone is involved in this response, and what is the name of this phenomenon?

Accepted Answer

Auxin; phototropism

Question 9

Which hormone slows the aging of plant organs by inhibiting protein breakdown and stimulating RNA and protein synthesis?

Accepted Answer

Cytokinins

Question 10

A plant exposed to mechanical stress produces a hormone that induces the triple response. What are the three components of this response?

Accepted Answer

Slowing of stem elongation, thickening of the stem, and horizontal growth

Question 11

Which hormone is chemically similar to cholesterol and animal sex hormones, and what is its primary function in plants?

Accepted Answer

Brassinosteroids; induce cell elongation and division in stem segments

Question 12

A plant growing in darkness exhibits elongated stems and lacks healthy roots. What is this adaptation called, and what changes occur when the plant is exposed to light?

Accepted Answer

Etiolation; de-etiolation occurs with normal shoot and root growth

Question 13

Which photoreceptor is responsible for regulating seed germination and shade avoidance, and how does it respond to red and far-red light?

Accepted Answer

Phytochrome; red light converts Pr to Pfr, far-red light converts Pfr to Pr

Question 14

A plant receives more far-red than red light due to shading by other plants. What response is triggered, and which phytochrome state is favored?

Accepted Answer

Shade avoidance response; Pr state is favored

Question 15

Which hormone is produced in actively growing tissues such as roots, embryos, and fruits, and works together with auxin to control cell division and differentiation?

Accepted Answer

Cytokinins

Question 16

A plant's leaves begin to fall in autumn. Which two hormones are involved in controlling leaf abscission, and what change in their balance triggers this process?

Accepted Answer

Auxin and ethylene; increased ethylene and decreased auxin trigger abscission

Question 17

Which hormone is released from the embryo after water is imbibed, signaling seeds to germinate and mobilize stored reserves?

Accepted Answer

Gibberellins

Question 18

A plant's arrangement of leaves on the stem (phyllotaxy) is disrupted. Which hormone's transport is most likely affected?

Accepted Answer

Auxin

Question 19

Which hormone is most likely to be used to increase the size of seedless grapes in commercial agriculture?

Accepted Answer

Gibberellins

Question 20

A plant exposed to blue light exhibits phototropism and stomatal opening. Which class of photoreceptors mediates these responses?

Accepted Answer

Blue-light photoreceptors

Plant Responses to Internal and External Signals: Plant Hormones and Light Responses

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