Part 6 — Plant Growth Regulators: Auxin, Gibberellin, Cytokinin

Part 6 – Plant Growth Regulators: Auxin, Gibberellin, Cytokinin

Q1. Which plant hormone was first discovered in oat coleoptile experiments by F.W. Went?

a) Gibberellin
b) Auxin
c) Cytokinin
d) Ethylene

Answer: b) Auxin

a) Gibberellin – Incorrect: Discovered later in Gibberella fujikuroi fungus.
b) Auxin – Correct: Went’s Avena curvature test confirmed auxin in oat coleoptiles.
c) Cytokinin – Incorrect: First discovered as kinetin in DNA hydrolysate.
d) Ethylene – Incorrect: Known earlier as a gas influencing fruit ripening.

Q2. The natural auxin found in plants is:

a) IAA (Indole-3-acetic acid)
b) IBA (Indole-3-butyric acid)
c) NAA (Naphthalene acetic acid)
d) 2,4-D (2,4-Dichlorophenoxyacetic acid)

Answer: a) IAA

a) IAA – Correct: The main naturally occurring auxin in plants.
b) IBA – Incorrect: Naturally present in small amounts but used mainly in rooting.
c) NAA – Incorrect: Synthetic auxin used in agriculture.
d) 2,4-D – Incorrect: Synthetic herbicide, not a natural auxin.

Q3. Which of the following is a synthetic auxin commonly used as a herbicide?

a) IAA
b) NAA
c) 2,4-D
d) Gibberellic acid

Answer: c) 2,4-D

a) IAA – Incorrect: Natural auxin, not herbicidal.
b) NAA – Incorrect: Used for fruit setting, not as herbicide.
c) 2,4-D – Correct: Selective herbicide for broad-leaved weeds.
d) Gibberellic acid – Incorrect: Not an auxin, belongs to gibberellins.

Q4. Which plant hormone promotes apical dominance?

a) Auxin
b) Cytokinin
c) Gibberellin
d) Ethylene

Answer: a) Auxin

a) Auxin – Correct: Produced in apical bud; suppresses lateral buds.
b) Cytokinin – Incorrect: Promotes lateral bud growth (antagonistic to auxin).
c) Gibberellin – Incorrect: Stimulates elongation, not apical dominance.
d) Ethylene – Incorrect: Promotes lateral growth and senescence.

Q5. Which of the following auxins is used for inducing root formation in cuttings?

a) 2,4-D
b) IBA
c) Kinetin
d) GA₃

Answer: b) IBA

a) 2,4-D – Incorrect: Used as herbicide, not for rooting.
b) IBA – Correct: Induces adventitious root formation.
c) Kinetin – Incorrect: Cytokinin, not involved in rooting.
d) GA₃ – Incorrect: Involved in stem elongation, not rooting.

Q6. Gibberellins were first discovered in association with which disease of rice?

a) Blight
b) Bakanae
c) Blast
d) Rust

Answer: b) Bakanae

a) Blight – Incorrect: Caused by bacterial/fungal infections.
b) Bakanae – Correct: Caused by Gibberella fujikuroi fungus → excessive elongation.
c) Blast – Incorrect: Caused by Pyricularia oryzae.
d) Rust – Incorrect: A fungal disease, unrelated to gibberellins.

Q7. Which plant hormone is used for breaking seed dormancy?

a) Auxin
b) Gibberellin
c) Cytokinin
d) ABA

Answer: b) Gibberellin

a) Auxin – Incorrect: Not involved in dormancy breaking.
b) Gibberellin – Correct: Breaks seed and bud dormancy.
c) Cytokinin – Incorrect: Involved in cell division.
d) ABA – Incorrect: Induces dormancy.

Q8. Which hormone is responsible for bolting in rosette plants like cabbage?

a) Auxin
b) Gibberellin
c) Cytokinin
d) ABA

Answer: b) Gibberellin

a) Auxin – Incorrect: Not involved in bolting.
b) Gibberellin – Correct: Promotes bolting and flowering in long-day plants.
c) Cytokinin – Incorrect: No role in bolting.
d) ABA – Incorrect: Growth inhibitor.

Q9. Which of the following is NOT a role of gibberellins?

a) Stem elongation
b) Fruit elongation
c) Apical dominance
d) Breaking dormancy

Answer: c) Apical dominance

a) Stem elongation – Correct role of gibberellins.
b) Fruit elongation – Correct role (e.g., grapes).
c) Apical dominance – Incorrect, role of auxin.
d) Breaking dormancy – Correct role.

Q10. Which hormone induces parthenocarpy in tomatoes?

a) Auxin
b) Gibberellin
c) Cytokinin
d) ABA

Answer: a) Auxin

a) Auxin – Correct: Artificially applied auxin induces seedless fruits.
b) Gibberellin – Incorrect: Also induces parthenocarpy but less common in tomato.
c) Cytokinin – Incorrect: Promotes cell division, not parthenocarpy.
d) ABA – Incorrect: Growth inhibitor.

Q11. The commercial production of seedless grapes is due to the application of:

a) Auxin
b) Gibberellin
c) Cytokinin
d) Ethylene

Answer: b) Gibberellin

a) Auxin – Incorrect: Majorly for tomato parthenocarpy.
b) Gibberellin – Correct: Produces larger, seedless grapes.
c) Cytokinin – Incorrect: Not related to parthenocarpy.
d) Ethylene – Incorrect: Involved in ripening.

Q12. Cytokinins were first discovered in:

a) Coconut milk
b) Corn kernels
c) Tobacco pith culture
d) Oat coleoptiles

Answer: c) Tobacco pith culture

a) Coconut milk – Incorrect: Contains natural cytokinins, but discovery was from kinetin.
b) Corn kernels – Incorrect: Source of natural zeatin, discovered later.
c) Tobacco pith culture – Correct: Skoog and Miller discovered kinetin.
d) Oat coleoptiles – Incorrect: Related to auxin experiments.

Q13. The naturally occurring cytokinin in plants is:

a) Zeatin
b) Kinetin
c) BAP (Benzylaminopurine)
d) NAA

Answer: a) Zeatin

a) Zeatin – Correct: Discovered from maize kernels.
b) Kinetin – Incorrect: Synthetic, discovered in DNA hydrolysate.
c) BAP – Incorrect: Synthetic cytokinin used in tissue culture.
d) NAA – Incorrect: Synthetic auxin, not cytokinin.

Q14. Which of the following hormones promotes chloroplast development?

a) Auxin
b) Gibberellin
c) Cytokinin
d) Ethylene

Answer: c) Cytokinin

a) Auxin – Incorrect: Mainly elongation, not chloroplast development.
b) Gibberellin – Incorrect: Not directly related to chloroplasts.
c) Cytokinin – Correct: Promotes chloroplast differentiation.
d) Ethylene – Incorrect: Promotes senescence, opposite effect.

Q15. The ratio of auxin to cytokinin in tissue culture determines:

a) Apical dominance
b) Type of organ formed
c) Bolting
d) Fruit ripening

Answer: b) Type of organ formed

a) Apical dominance – Incorrect: Controlled by auxin alone.
b) Type of organ formed – Correct: High auxin: root, high cytokinin: shoot.
c) Bolting – Incorrect: Controlled by gibberellin.
d) Fruit ripening – Incorrect: Controlled by ethylene.

Q16. Cytokinins delay which physiological process?

a) Apical dominance
b) Senescence
c) Bolting
d) Fruit set

Answer: b) Senescence

a) Apical dominance – Incorrect: Auxin related.
b) Senescence – Correct: Cytokinins are anti-senescence hormones.
c) Bolting – Incorrect: Controlled by gibberellin.
d) Fruit set – Incorrect: Auxin related.

Q17. Which of the following is TRUE regarding cytokinins?

a) They inhibit cell division
b) They promote apical dominance
c) They promote lateral bud growth
d) They induce abscission

Answer: c) They promote lateral bud growth

a) Inhibit cell division – Incorrect: They stimulate cell division.
b) Promote apical dominance – Incorrect: Opposite effect.
c) Promote lateral bud growth – Correct: Antagonistic to auxin.
d) Induce abscission – Incorrect: Ethylene is responsible.

Q18. Which of the following is NOT a cytokinin?

a) Zeatin
b) Kinetin
c) BAP
d) IBA

Answer: d) IBA

a) Zeatin – Correct cytokinin.
b) Kinetin – Correct cytokinin.
c) BAP – Correct synthetic cytokinin.
d) IBA – Incorrect, this is an auxin.

Q19. The antagonistic relationship in controlling apical dominance is between:

a) Auxin and gibberellin
b) Auxin and cytokinin
c) Cytokinin and ABA
d) Gibberellin and ABA

Answer: b) Auxin and cytokinin

a) Auxin & gibberellin – Incorrect: Both promote growth.
b) Auxin & cytokinin – Correct: Auxin → apical dominance; Cytokinin → lateral growth.
c) Cytokinin & ABA – Incorrect: Not directly related.
d) Gibberellin & ABA – Incorrect: Work oppositely in dormancy.

Q20. Which of the following hormones promotes nutrient mobilization in senescing leaves?

a) Auxin
b) Gibberellin
c) Cytokinin
d) ABA

Answer: c) Cytokinin

a) Auxin – Incorrect: Not involved.
b) Gibberellin – Incorrect: Role in elongation.
c) Cytokinin – Correct: Delays senescence and mobilizes nutrients.
d) ABA – Incorrect: Causes senescence.

Q21. Which of the following is incorrectly matched?

a) Auxin – Apical dominance
b) Gibberellin – Bolting
c) Cytokinin – Senescence promotion
d) IBA – Root initiation

Answer: c) Cytokinin – Senescence promotion

a) Auxin – Apical dominance – Correct.
b) Gibberellin – Bolting – Correct.
c) Cytokinin – Senescence promotion – Incorrect, cytokinins delay senescence.
d) IBA – Root initiation – Correct.

Q22. Which hormone is used in tissue culture to induce shoot formation?

a) High auxin, low cytokinin
b) High cytokinin, low auxin
c) Equal auxin and cytokinin
d) Gibberellin

Answer: b) High cytokinin, low auxin

a) High auxin, low cytokinin – Incorrect: Root formation.
b) High cytokinin, low auxin – Correct: Shoot formation.
c) Equal – Incorrect: Callus formation.
d) Gibberellin – Incorrect: Not used in organogenesis.

Q23. The “foolish seedling” disease in rice is due to excess:

a) Auxin
b) Cytokinin
c) Gibberellin
d) Ethylene

Answer: c) Gibberellin

a) Auxin – Incorrect.
b) Cytokinin – Incorrect.
c) Gibberellin – Correct, causes abnormal elongation.
d) Ethylene – Incorrect.

Q24. Which hormone works synergistically with auxin in cell elongation?

a) Cytokinin
b) Gibberellin
c) Ethylene
d) ABA

Answer: b) Gibberellin

a) Cytokinin – Incorrect: Works in division, not elongation.
b) Gibberellin – Correct: Promotes elongation along with auxin.
c) Ethylene – Incorrect: Usually inhibits elongation.
d) ABA – Incorrect: Growth inhibitor.

Q25. Which statement is correct regarding auxin transport?

a) It is non-polar and bidirectional
b) It is polar and unidirectional
c) It is only passive diffusion
d) It occurs via xylem

Answer: b) It is polar and unidirectional

a) Non-polar – Incorrect.
b) Polar & unidirectional – Correct, basipetal transport.
c) Only passive – Incorrect, involves active transport.
d) Via xylem – Incorrect, not related to transpiration stream.

Plant Growth Class 11, Biology Growth Regulators, CBSE Biology Notes, Class 11 NEET MCQs, NCERT Plant Growth, Seed Germination Biology, Differentiation Redifferentiation, Plant Growth NEET Preparation, plant growth and development mcqs for neet, cbse class 11 biology plant growth notes, auxin gibberellin cytokinin neet questions, seed germination class 11 biology mcqs, differentiation and dedifferentiation examples biology, plant growth regulators mcqs for neet ug, conditions of plant growth ncert biology, phases of growth class 11 ncert questions

Part 6 — Plant Growth Regulators: Auxin, Gibberellin, Cytokinin