arrow_backBack to Study Resources

Quiz Chapter 5: Response in Plants

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

Question 1 of 10Score: 0

Which phytohormone promotes leaf fall (abscission) and fruit drop in mature plants?

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 promotes leaf fall (abscission) and fruit drop in mature plants?

  1. Cytokinin
  2. Gibberellin
  3. Ethylene
  4. Auxin
Show answer

Answer: C

Ethylene (along with falling auxin levels) stimulates enzyme activity in the abscission zone, causing leaf and fruit drop.

2. 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.

3. 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
Show answer

Answer: A

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

4. 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
Show answer

Answer: B

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

5. 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
Show answer

Answer: B

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

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.
Show answer

Answer: B

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

7. 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.

8. What is parthenocarpy?

  1. The growth of roots toward soil moisture
  2. The development of seedless fruits without prior fertilization
  3. The shedding of leaves during seasonal autumn
  4. The rapid germination of dormant spores
Show answer

Answer: B

Parthenocarpy is the process of producing seedless fruits without fertilization, often artificially induced by applying auxin or gibberellin.

9. 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
Show answer

Answer: B

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

10. 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.
Show answer

Answer: B

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

Sponsored