Plant hormones and responses (tropisms) Knowledge-Based Practice

Questions

1. 1.

   Which plant hormone promotes seed germination by breaking dormancy and stimulating the production of digestive enzymes, such as $\alpha$-amylase, to mobilize stored endosperm nutrients?

   • A) Abscisic acid
   • B) Gibberellin
   • C) Cytokinin
   • D) Ethylene
2. 2.

   Tendrils of climbing vines coil tightly around physical supports to anchor the plant as it grows upward. Which physiological mechanism directly produces this directional growth response known as thigmotropism?

   • A) Rapid, reversible turgor pressure changes within specialized motor cells at the base of the petiole
   • B) Differential cell elongation, in which cells on the outer, non-contact side grow faster than cells touching the support
   • C) Uniform shrinkage of xylem vessels along the length of the tendril triggered by sudden abscisic acid synthesis
   • D) Symmetrical acceleration of mitotic cell divisions across all cell layers stimulated by localized cytokinin release
3. 3.

   During periods of severe soil water deficit, which plant hormone acts as a critical stress signal that induces the rapid closure of stomata to prevent excessive water loss?

   • A) Gibberellin
   • B) Cytokinin
   • C) Abscisic acid
   • D) Ethylene
4. 4.

   When a seedling is placed horizontally, auxin accumulates along the lower side of its primary root. How does this uneven hormone distribution bring about positive gravitropism in the root?

   • A) Auxin stimulates localized cell division on the lower side, forcing the root tip downward.
   • B) Auxin inhibits cell elongation on the lower side, allowing cells on the upper side to elongate faster and curve the root downward.
   • C) Auxin accelerates cell elongation on the lower side, pushing the apex of the root down into the soil.
   • D) Auxin dissolves the primary cell walls on the upper side, causing structural collapse that tilts the root downward.
5. 5.

   Which of the following describes the mechanism by which auxin mediates positive phototropism in growing plant shoots exposed to unilateral light?

   • A) Auxin is broken down on the shaded side, allowing cells on the illuminated side to divide more rapidly.
   • B) Auxin concentrates on the illuminated side, inhibiting the expansion of cell walls exposed to light.
   • C) Auxin accumulates on the shaded side, promoting increased cell elongation on that side relative to the illuminated side.
   • D) Auxin remains evenly distributed, inducing uniform differentiation across both sides of the stem.

Answers and step-by-step solutions appear after you finish the test.