Question 1

Buds and sprouts often form on tree stumps. Which of the following hormones would you expect to stimulate their formation?

Accepted Answer

Cytokinins stimulate cell division and differentiation, leading to the formation of buds and sprouts. Auxin may also play a role in promoting their growth, but cytokinins are the primary hormone involved. Abscisic acid and ethylene are involved in stress responses and growth inhibition, while gibberellins promote stem elongation and fruit development.

Question 2

This experiment suggests that the unknown amount of gibberellin in the experimental plant (B)is approximately

Accepted Answer

The experimental plant (B) had a height similar to the control plants indicating that it did not have any excess gibberellin. The concentration of gibberellin in the shortest plant was determined to be 0.1 μg/mL. Therefore, the best choice is C, 0.1 μg/mL, which is equal to the amount of gibberellin in the shortest plant.

Question 3

Which plant hormones might be used to enhance stem elongation and fruit growth?

Accepted Answer

Auxins and gibberellins are known to promote stem elongation and fruit growth. Auxins stimulate cell elongation and differentiation, while gibberellins promote cell division and elongation. Together, they can enhance the overall growth and development of the plant.

Question 4

Auxins (IAA)in plants are known to affect all of the following phenomena except

Accepted Answer

Auxins are known to affect geotropism of shoots, phototropism of shoots, inhibition of lateral buds, and fruit development, but they are not known to affect the maintenance of dormancy.

Question 5

How does indoleacetic acid affect fruit development?

Accepted Answer

Indoleacetic acid, a type of auxin, plays an important role in promoting rapid growth of the ovary, which leads to fruit development. It helps in initiating cell division and elongation in the developing fruit, resulting in its growth and maturation.

Question 6

Which of the following has not been established as an aspect of auxin's role in cell elongation?

Accepted Answer

While auxin does play a role in cell elongation, it does not increase the quantity of cytoplasm in the cell. Auxin primarily affects cell elongation by instigating a loosening of cell wall fibers, increasing the size of vacuoles, permitting an increase in turgor pressure, and stimulating proton pumps.

Question 7

Figure 39.1
-The heavy line in Figure 39.1 illustrates the relationship between auxin concentration and cell growth in stem tissues. If the same range of concentrations were applied to lateral buds, what curve would probably be produced?

Accepted Answer

The answer of  Figure 39.1
-The heavy line in Figure...

Question 8

According to the acid growth hypothesis, auxin works by

Accepted Answer

The acid growth hypothesis proposes that auxin causes acidification of the cell wall, which activates enzymes that loosen the cell wall and increase its plasticity. This allows the affected cell walls to elongate, leading to growth. Therefore, option D, increasing wall plasticity and allowing the affected cell walls to elongate, best describes the action of auxin according to this hypothesis.

Question 9

Which of the following hormones would be most useful in promoting the rooting of plant cuttings?

Accepted Answer

Auxins are plant hormones that play a major role in promoting cell elongation and division. They are particularly effective in promoting the formation of roots in cuttings.

Question 10

Why might animal hormones function differently from plant hormones?

Accepted Answer

Animal hormones function differently because animals can move rapidly away from negative stimuli, unlike most plants, and plants exhibit more variability in morphology and development, requiring different hormonal regulation.

Question 11

Oat seedlings are sometimes used to study auxins because

Accepted Answer

Oat seedlings are commonly used in studies involving auxins because their coleoptile (the protective sheath covering the emerging shoot) shows a strong positive phototropism, meaning it grows towards light. This characteristic makes it easier to observe and measure the effects of auxins, which are plant hormones that play a crucial role in directing plant growth towards light.

Question 12

Cells elongate in response to auxin. All of the following are part of the acid growth hypothesis except

Accepted Answer

The acid growth hypothesis proposes that auxin stimulates proton pumps in cell membranes, which results in lowered pH and the breakage of cross-links between cellulose microfibrils. As a result, the wall fabric becomes looser and more plastic, allowing the cell to elongate when the turgor pressure exceeds the restraining pressure of the loosened cell wall. However, the hypothesis does not propose that auxin-activated proton pumps stimulate cell division in meristems.

Question 13

The synthesis of which of the following hormones would be a logical first choice in an attempt to produce normal growth in mutant dwarf plants?

Accepted Answer

Gibberellin is the hormone responsible for stem elongation and promoting cell division and growth in plants. Mutant dwarf plants typically have deficiencies in gibberellin, so adding this hormone would be a logical first choice to try and promote normal growth.

Question 14

The results of this experiment, shown on the left of the graph (area

Accepted Answer

The graph shows a clear correlation between plant height and gibberellin concentration, indicating that gibberellin is likely necessary for plant growth and height. The graph does not provide evidence for the other options.

Question 15

Which plant hormone(s)is (are)most closely associated with cell division?

Accepted Answer

Cytokinin is the plant hormone most closely associated with cell division. It stimulates mitosis and cell division in plant tissues.

Question 16

Auxin triggers the acidification of cell walls that results in rapid growth, but also stimulates sustained, long-term cell elongation. What best explains how auxin brings about this dual growth response?

Accepted Answer

Auxin triggers the activation of certain genes that promote sustained long-term cell elongation, but also activates proton pumps that result in rapid growth through acidification of cell walls. This dual effect is brought about through the activation of second messengers by auxin.

Question 17

Plant growth regulators can be characterized by all of the following except that they

Accepted Answer

Plant growth regulators do not function independently of other hormones; rather, they interact with other hormones and signaling pathways to control growth and development.

Question 18

Plant hormones can have different effects at different concentrations. This explains how

Accepted Answer

Auxin is a plant hormone that can have different effects at different concentrations. At low concentrations, it stimulates cell elongation in apical meristems, while at high concentrations, it inhibits the growth of axillary buds. This is an example of how plant hormones can have different effects depending on their concentration.

Question 19

Plant hormones produce their effects by

Accepted Answer

Plant hormones work by altering the expression of genes and modifying the permeability of the plasma membrane. These two mechanisms are the primary ways in which plant hormones produce their effects. Hormones can affect gene expression by binding to specific receptors and activating or inhibiting genes that control different physiological processes. Hormones can also modify the plasma membrane, making it more or less permeable to certain molecules, which can affect cellular processes such as nutrient uptake or water conservation.

Question 20

Why do coleoptiles grow toward light?

Accepted Answer

Auxin, a plant hormone, redistributes to the shady side of the plant when exposed to light. This uneven distribution causes the cells on the darker side to elongate more than those on the light-exposed side, leading to the plant bending towards the light.

Quiz 39: Plant Responses to Internal and External Signals