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Quiz Chapter 5: Response in Plants

10 questions · Form 5 Biology Bab 5: Response in Plants

10 questions · plays in fullscreen

Full Question List & Answer Key

Prefer reading to quizzing? All 10 questions are listed below with the answer and explanation under each one.

1. Which phytohormone delays leaf senescence (aging) by keeping leaves green longer?

  1. Cytokinin
  2. Abscisic acid
  3. Ethylene
  4. Synthetic 2,4-D
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Answer: A

Cytokinins delay leaf aging (senescence) by promoting nutrient mobilization and maintaining protein/chlorophyll stability.

2. What phenomenon occurs when a main apical shoot tip suppresses the growth of lateral side buds?

  1. Apical dominance
  2. Parthenocarpy
  3. Senescence
  4. Photoperiodism
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Answer: A

Apical dominance is driven by high auxin produced at the apical tip diffusing downward to inhibit axillary bud growth.

3. What effect does gibberellin application have on commercial table grape crops?

  1. Produces small, tightly packed, sour berries
  2. Increases internode/pedicel length and produces larger, well-spaced grapes
  3. Causes immediate leaf loss and fruit drop
  4. Prevents fruit formation completely
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Answer: B

Gibberellin application elongates fruit stalks (pedicels), giving individual grapes more room to grow larger without overcrowding.

4. What key feature distinguishes a nastic response from a tropism response?

  1. Nastic responses are permanent cell growth movements.
  2. Nastic responses are non-directional and independent of the stimulus direction.
  3. Nastic responses are driven purely by mitotic cell division.
  4. Nastic responses occur exclusively in root tip meristems.
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Answer: B

Nastic responses are rapid, reversible, non-directional movements caused by turgor pressure changes, whereas tropisms are directional growth responses.

5. What type of response is shown by the sudden folding of Mimosa pudica leaflets when touched?

  1. Positive Thigmotropism
  2. Seismonastic / Thigmonastic response
  3. Negative Geotropism
  4. Photonastic response
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Answer: B

The rapid folding of Mimosa leaves is a non-directional, reversible seismonastic response caused by sudden loss of turgor pressure in pulvinus cells.

6. How does auxin (IAA) distribution change when a shoot tip receives unilateral light?

  1. Auxin breaks down completely under light.
  2. Auxin diffuses laterally to accumulate on the shaded side of the shoot tip.
  3. Auxin concentrates exclusively on the illuminated side.
  4. Auxin moves into root tissues via active transport.
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Answer: B

Unilateral light causes auxin to migrate laterally away from light to the shaded side, promoting faster cell elongation on that side.

7. Which phytohormone induces rapid stomatal closure in response to severe drought stress?

  1. Gibberellin
  2. Abscisic acid (ABA)
  3. Auxin (IAA)
  4. Cytokinin
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Answer: B

Abscisic acid acts as a plant stress hormone that signals guard cells to lose turgor pressure, closing stomata to conserve water.

8. Why do tendrils of climbing plants (e.g., passion flowers) coil around external support structures?

  1. In response to light intensity changes (Photonasty)
  2. Due to positive thigmotropism where touch inhibits growth on the contact side while the outer side elongates faster
  3. To absorb water directly from the support surface
  4. Due to negative gravitropism acting on root caps
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Answer: B

Touch contact triggers differential growth; cells on the outer non-contact side elongate faster, causing the tendril to coil around the support.

9. What movement is exhibited when pollen tubes grow toward chemical signals released by the embryo sac in an ovule?

  1. Positive Chemotropism
  2. Negative Phototropism
  3. Seismonasty
  4. Thermonasty
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Answer: A

Pollen tube growth toward ovules is a directional growth response guided by a chemical concentration gradient (positive chemotropism).

10. What happens to a shoot tip when its apical bud is cut off (decapitated)?

  1. The stem elongates at ten times its normal speed.
  2. Apical dominance is broken, allowing axillary lateral buds to grow into branches.
  3. The plant immediately dies from auxin toxicity.
  4. Root growth stops completely within minutes.
Show answer

Answer: B

Removing the apical tip removes the primary source of auxin, releasing lateral buds from inhibition and promoting bushy branching.

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