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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. What causes the reversible folding of leaves in leguminous plants at dusk (nyctinasty)?

  1. Cell division in the apical meristem
  2. Changes in turgor pressure in pulvinus joint cells at the leaf base
  3. Rapid synthesis of lignin in petiole cell walls
  4. Irreversible cell elongation on the upper leaf surface
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Answer: B

Nyctinastic sleep movements are regulated by reversible osmotic water loss and turgor changes in specialized pulvinus cells.

2. 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).

3. 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.

4. 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.
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Answer: B

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

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 is commonly applied in commercial rooting powders to induce root formation on stem cuttings?

  1. Ethylene
  2. Auxin
  3. Abscisic acid
  4. Gibberellin
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Answer: B

Auxins stimulate the development of adventitious roots at the cut ends of plant stem cuttings.

8. Which phytohormone is a gas that accelerates fruit ripening?

  1. Ethylene
  2. Cytokinin
  3. Gibberellin
  4. Indole-3-acetic acid
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Answer: A

Ethylene is a unique gaseous phytohormone that promotes enzymatic breakdown of starches and fruit ripening.

9. 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.

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

  1. Gibberellin
  2. Abscisic acid (ABA)
  3. Auxin (IAA)
  4. Cytokinin
Show answer

Answer: B

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

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