1. The first discovered plant hormone is ____________.
A) Gibberellin
B) Cytokinin
C) Auxin
D) Abscisic acid
Answer: C
Explanation: Auxin was the first plant hormone discovered through phototropism experiments by Darwin, and later isolated by Frits Went.
2. Who demonstrated that plant shoots bend towards light due to a chemical substance?
A) Charles Darwin
B) Kurosawa
C) Frits Went
D) Miller
Answer: A
Explanation: Darwin and his son Francis showed phototropism in canary grass coleoptiles, suggesting a mobile chemical (later identified as auxin).
3. Who first isolated auxin from oat coleoptile tips?
A) Charles Darwin
B) Frits Went
C) Miller
D) Kurosawa
Answer: B
Explanation: In 1928, Went collected diffusible substance from coleoptile tips, naming it “auxin.”
4. The naturally occurring auxin in plants is ____________.
A) Indole-3-acetic acid (IAA)
B) Indole-3-butyric acid (IBA)
C) Naphthalene acetic acid (NAA)
D) 2,4-D
Answer: A
Explanation: IAA is the main natural auxin present in plants.
5. Which auxin is widely used for rooting in stem cuttings?
A) IAA
B) IBA
C) 2,4-D
D) Kinetin
Answer: B
Explanation: Indole-3-butyric acid is applied to induce root formation in cuttings.
6. Which of the following is a synthetic auxin?
A) IAA
B) IBA
C) NAA
D) Zeatin
Answer: C
Explanation: Naphthalene acetic acid (NAA) is a synthetic auxin.
7. The auxin responsible for apical dominance is mainly produced in ____________.
A) Roots
B) Shoot tips
C) Leaves
D) Flowers
Answer: B
Explanation: Auxins produced in the apical bud suppress growth of lateral buds.
8. The phenomenon of suppression of lateral buds by apical bud is called ____________.
A) Phototropism
B) Apical dominance
C) Geotropism
D) Senescence
Answer: B
Explanation: Auxins from apical bud inhibit lateral buds, maintaining apical dominance.
9. Removal of apical bud results in growth of lateral buds. This is called ____________.
A) Pinching
B) Decapitation
C) Pruning
D) Defoliation
Answer: B
Explanation: Removing apical bud reduces auxin effect, allowing lateral buds to grow.
10. Which synthetic auxin is used as a selective weedicide?
A) 2,4-D
B) NAA
C) IBA
D) Kinetin
Answer: A
Explanation: 2,4-dichlorophenoxyacetic acid kills broad-leaved dicots but not monocot crops.
11. Which hormone promotes cell elongation in shoots?
A) Auxin
B) Cytokinin
C) ABA
D) Ethylene
Answer: A
Explanation: Auxins promote loosening of cell wall, aiding elongation.
12. Which hormone promotes parthenocarpic fruit development?
A) Cytokinin
B) Gibberellin
C) Auxin
D) Ethylene
Answer: C
Explanation: Auxins induce fruit formation without fertilization.
13. Which hormone delays leaf abscission?
A) ABA
B) Ethylene
C) Auxin
D) Cytokinin
Answer: C
Explanation: Auxins prevent leaf and fruit drop by inhibiting abscission layer formation.
14. In tissue culture, auxins are mainly used for ____________.
A) Shoot differentiation
B) Root initiation
C) Senescence delay
D) Fruit ripening
Answer: B
Explanation: Auxins induce root formation from callus in tissue culture.
15. Which auxin is used to prevent premature fruit drop in orchards?
A) IAA
B) IBA
C) NAA
D) Zeatin
Answer: C
Explanation: Naphthalene acetic acid prevents abscission of developing fruits.
16. Which plant response is controlled by lateral movement of auxin?
A) Thigmotropism
B) Phototropism
C) Chemotropism
D) Nastic movement
Answer: B
Explanation: Auxins accumulate on the shaded side, causing bending towards light.
17. In geotropism, auxins move towards ____________.
A) Upper side
B) Lower side
C) Equal distribution
D) Leaves
Answer: B
Explanation: Auxins accumulate on lower side of root/shoot in response to gravity.
18. In roots, higher auxin concentration causes ____________.
A) Increased elongation
B) Inhibition of elongation
C) Parthenocarpy
D) Apical dominance
Answer: B
Explanation: Auxins promote elongation in shoots but inhibit elongation in roots.
19. Synthetic auxin commonly used for fruit thinning in apple and grape cultivation is ____________.
A) NAA
B) 2,4-D
C) IBA
D) Zeatin
Answer: A
Explanation: NAA prevents overcrowding of developing fruits.
20. The discovery of auxins was based on experiments on ____________.
A) Maize endosperm
B) Oat coleoptile
C) Rice seedlings
D) Wheat roots
Answer: B
Explanation: Went’s classic experiment used oat coleoptile tips to demonstrate auxin.
21. Which auxin is naturally occurring in maize and other cereals?
A) IBA
B) IAA
C) NAA
D) 2,4-D
Answer: B
Explanation: IAA is a universal natural auxin in higher plants.
22. Auxins promote vascular differentiation. This is important in ____________.
A) Root initiation
B) Secondary growth
C) Fruit ripening
D) Senescence
Answer: B
Explanation: Auxins help in formation of xylem and phloem tissues.
23. Auxins act by ____________.
A) Increasing cell wall plasticity
B) Inhibiting respiration
C) Closing stomata
D) Inhibiting protein synthesis
Answer: A
Explanation: Auxins activate proton pumps, loosen cell walls, and promote elongation.
24. The process of fruit development without fertilization under auxin treatment is ____________.
A) Apomixis
B) Parthenocarpy
C) Polyembryony
D) Pollination
Answer: B
Explanation: Auxins induce seedless fruit development.
25. Excessive application of auxins can cause ____________.
A) Early flowering
B) Leaf abscission
C) Root initiation
D) Increased seed germination
Answer: B
Explanation: Though auxins normally delay abscission, excess concentration reverses the effect, causing leaf and fruit drop.
26. Gibberellins were first discovered in ____________.
A) Maize kernels
B) Oat coleoptiles
C) Rice seedlings
D) Tobacco pith culture
Answer: C
Explanation: Kurosawa discovered gibberellin while studying “foolish seedling disease” in rice caused by Gibberella fujikuroi.
27. Which scientist is credited with the discovery of gibberellins?
A) Frits Went
B) Kurosawa
C) Miller
D) Darwin
Answer: B
Explanation: In 1926, Kurosawa linked abnormal growth in rice to a fungal metabolite, later named gibberellin.
28. The main physiological effect of gibberellins is ____________.
A) Root initiation
B) Cell division
C) Stem elongation
D) Fruit ripening
Answer: C
Explanation: Gibberellins break dormancy, induce bolting, and cause internode elongation.
29. Bolting in rosette plants like cabbage is due to ____________.
A) Auxin
B) Cytokinin
C) Gibberellin
D) Ethylene
Answer: C
Explanation: GA causes elongation of internodes leading to bolting before flowering.
30. Which hormone induces enzyme synthesis (amylase) during seed germination?
A) Auxin
B) Gibberellin
C) Cytokinin
D) Ethylene
Answer: B
Explanation: GA stimulates aleurone layer to produce hydrolytic enzymes that mobilize stored food.
31. Gibberellins can substitute for which environmental requirement to break seed dormancy?
A) Light
B) Low temperature
C) Water
D) Oxygen
Answer: B
Explanation: GA can replace cold stratification in seed germination.
32. Which hormone is commercially used to increase sugarcane yield?
A) Auxin
B) Gibberellin
C) Cytokinin
D) Ethylene
Answer: B
Explanation: GA promotes stem elongation and enhances sugar accumulation in sugarcane.
33. The hormone responsible for “foolish seedling disease” is ____________.
A) Auxin
B) Cytokinin
C) Gibberellin
D) Ethylene
Answer: C
Explanation: Excess GA from fungal infection caused abnormal tall growth in rice seedlings.
34. Which gibberellin is most biologically active?
A) GA₁
B) GA₂
C) GA₃
D) GA₇
Answer: C
Explanation: GA₃ is widely used commercially and physiologically most active.
35. Gibberellins induce seedless fruit formation (parthenocarpy) in ____________.
A) Tomato
B) Banana
C) Grapes
D) Pineapple
Answer: C
Explanation: GA sprays are used to induce seedlessness in grapes.
36. Which of the following is a cytokinin?
A) Indole-3-acetic acid
B) Zeatin
C) Gibberellin A₃
D) Abscisic acid
Answer: B
Explanation: Zeatin is a natural cytokinin isolated from maize kernels.
37. Cytokinins were first discovered by ____________.
A) Frits Went
B) Kurosawa
C) Miller
D) Darwin
Answer: C
Explanation: In 1955, Miller discovered kinetin while studying DNA extracts.
38. The first cytokinin discovered was ____________.
A) Zeatin
B) Kinetin
C) 6-BA
D) Zeatin riboside
Answer: B
Explanation: Kinetin was obtained from autoclaved herring sperm DNA.
39. The main function of cytokinins is ____________.
A) Root elongation
B) Flower induction
C) Cell division
D) Fruit ripening
Answer: C
Explanation: Cytokinins are also called “cell division hormones.”
40. In tissue culture, a high cytokinin to auxin ratio favors ____________.
A) Root formation
B) Shoot formation
C) Callus initiation
D) Senescence
Answer: B
Explanation: Cytokinins promote shoot differentiation, whereas auxins promote roots.
41. Cytokinins delay ____________.
A) Senescence
B) Flowering
C) Apical dominance
D) Dormancy
Answer: A
Explanation: Cytokinins are also called anti-aging hormones as they delay leaf yellowing.
42. Natural cytokinin found in maize kernels is ____________.
A) Kinetin
B) Zeatin
C) IBA
D) NAA
Answer: B
Explanation: Zeatin is the most common natural cytokinin.
43. Cytokinins are synthesized mainly in ____________.
A) Root tips
B) Shoot apices
C) Leaves
D) Flowers
Answer: A
Explanation: Cytokinins are synthesized in root tips and transported upward via xylem.
44. Which hormone promotes nutrient mobilization in plants?
A) Cytokinin
B) Auxin
C) Gibberellin
D) Ethylene
Answer: A
Explanation: Cytokinins mobilize nutrients towards young leaves, fruits, and seeds.
45. Cytokinins overcome apical dominance caused by ____________.
A) Auxins
B) Gibberellins
C) Ethylene
D) ABA
Answer: A
Explanation: Cytokinins promote lateral bud growth, counteracting auxin effect.
46. Which hormone is used to increase shelf life of vegetables?
A) Auxin
B) Gibberellin
C) Cytokinin
D) ABA
Answer: C
Explanation: Cytokinins delay senescence and extend freshness of vegetables.
47. Coconut milk contains ____________.
A) Auxins
B) Cytokinins
C) Gibberellins
D) Ethylene
Answer: B
Explanation: Coconut milk is rich in natural cytokinins and used in tissue culture.
48. High auxin to cytokinin ratio in tissue culture leads to ____________.
A) Callus
B) Root formation
C) Shoot formation
D) Senescence
Answer: B
Explanation: Root initiation requires high auxin relative to cytokinin.
49. Cytokinins are chemically derivatives of ____________.
A) Indole
B) Purine (adenine)
C) Carotenoids
D) Amino acids
Answer: B
Explanation: Cytokinins are adenine derivatives, e.g., kinetin, zeatin.
50. Which pair of hormones acts antagonistically in bud growth regulation?
A) Auxin & Cytokinin
B) Gibberellin & Cytokinin
C) ABA & Cytokinin
D) Ethylene & Gibberellin
Answer: A
Explanation: Auxin maintains apical dominance, while cytokinin promotes lateral bud growth.
51. Which is the only gaseous plant hormone?
A) Cytokinin
B) Ethylene
C) Auxin
D) Gibberellin
Answer: B
Explanation: Ethylene is a simple gaseous hydrocarbon (C₂H₄) acting as a plant hormone.
52. Which hormone is responsible for fruit ripening?
A) Auxin
B) Ethylene
C) Cytokinin
D) Gibberellin
Answer: B
Explanation: Ethylene regulates ripening of climacteric fruits like banana, mango, and tomato.
53. Ethylene induces ____________.
A) Seed dormancy
B) Flowering in pineapple
C) Apical dominance
D) Root elongation
Answer: B
Explanation: Ethylene induces synchronized flowering in pineapple plantations.
54. Which hormone is used to ripen fruits artificially?
A) Auxin
B) Gibberellin
C) Ethylene
D) Cytokinin
Answer: C
Explanation: Commercial ethylene or ethrel sprays are used to ripen fruits.
55. Ethylene promotes ____________.
A) Apical dominance
B) Senescence and abscission
C) Stem elongation
D) Phototropism
Answer: B
Explanation: Ethylene accelerates leaf fall, flower drop, and aging.
56. Which hormone is used to increase latex yield in rubber plants?
A) Auxin
B) Gibberellin
C) Ethylene
D) Cytokinin
Answer: C
Explanation: Ethylene stimulates laticifer activity in rubber.
57. Ethylene promotes root initiation in ____________.
A) Tissue culture
B) Cuttings
C) Hydroponics
D) All of these
Answer: D
Explanation: Ethylene stimulates adventitious root formation.
58. Triple response of ethylene includes ____________.
A) Stem elongation, leaf expansion, senescence
B) Inhibition of elongation, stem swelling, horizontal growth
C) Apical dominance, bolting, parthenocarpy
D) Fruit ripening, seed dormancy, bolting
Answer: B
Explanation: This response was first observed in pea seedlings.
59. Ethylene production is highest in ____________.
A) Roots
B) Flowers
C) Ripening fruits
D) Leaves
Answer: C
Explanation: Climacteric fruits produce maximum ethylene during ripening.
60. Ethylene is commercially available as ____________.
A) IAA
B) NAA
C) Ethrel
D) Zeatin
Answer: C
Explanation: Ethrel (2-chloroethyl phosphonic acid) releases ethylene in plant tissues.
61. Ethylene promotes female flowers in ____________.
A) Papaya
B) Cucurbits
C) Maize
D) Sugarcane
Answer: B
Explanation: Ethylene increases female flowers in cucumber and pumpkin.
62. Ethylene enhances the rate of ____________.
A) Transpiration
B) Respiration
C) Photosynthesis
D) Mineral uptake
Answer: B
Explanation: Ethylene increases respiration during fruit ripening.
63. Ethylene delays ____________.
A) Abscission
B) Senescence
C) Flowering
D) None of these
Answer: D
Explanation: Ethylene promotes abscission and senescence, not delay them.
64. Which hormone is called the “stress hormone”?
A) Auxin
B) Gibberellin
C) Abscisic acid
D) Cytokinin
Answer: C
Explanation: ABA accumulates under stress (drought, cold, salinity).
65. Abscisic acid was initially called ____________.
A) Kinetin
B) Dormin
C) Zeatin
D) Florigen
Answer: B
Explanation: ABA was named “dormin” due to its role in seed dormancy.
66. Which hormone induces stomatal closure during drought?
A) Ethylene
B) Cytokinin
C) Abscisic acid
D) Auxin
Answer: C
Explanation: ABA prevents water loss by closing stomata.
67. ABA is antagonistic to ____________.
A) Auxin
B) Gibberellin
C) Cytokinin
D) Ethylene
Answer: B
Explanation: GA promotes germination, ABA induces dormancy.
68. ABA is synthesized mainly in ____________.
A) Young leaves
B) Root cap and mature leaves
C) Apical buds
D) Seeds only
Answer: B
Explanation: ABA is produced in stressed leaves and transported via phloem/xylem.
69. Which hormone inhibits seed germination?
A) Auxin
B) Gibberellin
C) ABA
D) Cytokinin
Answer: C
Explanation: ABA induces dormancy and prevents precocious germination.
70. Which hormone increases seed dormancy in cereals?
A) Auxin
B) Gibberellin
C) ABA
D) Cytokinin
Answer: C
Explanation: ABA maintains dormancy in wheat, rice, barley seeds.
71. Which hormone promotes abscission of leaves and fruits?
A) Cytokinin
B) Gibberellin
C) Abscisic acid
D) IAA
Answer: C
Explanation: ABA accelerates senescence and abscission.
72. ABA plays a major role in ____________.
A) Senescence
B) Flowering
C) Fruit ripening
D) Phototropism
Answer: A
Explanation: ABA induces leaf aging and death.
73. ABA inhibits ____________.
A) Fruit ripening
B) Stomatal closure
C) Senescence
D) Dormancy
Answer: A
Explanation: ABA generally delays fruit ripening unlike ethylene.
74. Vivipary (precocious seed germination) is due to ____________.
A) High ABA
B) Low ABA
C) High GA
D) Both B and C
Answer: D
Explanation: Vivipary (as in mangroves) occurs due to low ABA and high GA.
75. Which hormone acts as a “universal inhibitor” of plant growth?
A) Auxin
B) Cytokinin
C) Gibberellin
D) Abscisic acid
Answer: D
Explanation: ABA inhibits growth and is termed the universal growth inhibitor.
76. Which hormone is used to induce synchronized flowering in pineapple?
A) Auxin
B) Gibberellin
C) Ethylene
D) Cytokinin
Answer: C
Explanation: Ethylene spray ensures uniform flowering in pineapple fields.
77. Bolting in rosette plants (cabbage, lettuce) is induced by ____________.
A) Auxin
B) Gibberellin
C) Cytokinin
D) ABA
Answer: B
Explanation: Gibberellins elongate internodes, converting rosette habit to bolting.
78. The pair of hormones that act antagonistically in seed germination is ____________.
A) Auxin & Cytokinin
B) Gibberellin & ABA
C) Ethylene & Cytokinin
D) Auxin & Ethylene
Answer: B
Explanation: GA promotes germination, while ABA maintains dormancy.
79. Callus differentiation in tissue culture depends on ____________.
A) High auxin concentration only
B) High cytokinin concentration only
C) Ratio of cytokinin to auxin
D) Ethylene concentration
Answer: C
Explanation: High cytokinin:auxin → shoots; High auxin:cytokinin → roots.
80. Florigen is a hypothetical hormone responsible for ____________.
A) Phototropism
B) Flowering
C) Senescence
D) Parthenocarpy
Answer: B
Explanation: Florigen is the postulated mobile flowering signal in plants.
81. Hormone mixture used in tissue culture for shoot regeneration ____________.
A) High auxin, low cytokinin
B) High cytokinin, low auxin
C) Equal auxin and cytokinin
D) Only gibberellin
Answer: B
Explanation: Cytokinins promote shoot development.
82. Which hormone promotes femaleness in cucumber flowers?
A) Auxin
B) Gibberellin
C) Ethylene
D) Cytokinin
Answer: C
Explanation: Ethylene increases female flowers in cucurbits.
83. Which hormone is used in malting industry for brewing beer?
A) Cytokinin
B) Ethylene
C) Gibberellin
D) Auxin
Answer: C
Explanation: GA induces hydrolytic enzymes in barley grains during malting.
84. Which hormone is used to increase fruit size in grapes?
A) Cytokinin
B) Gibberellin
C) Auxin
D) ABA
Answer: B
Explanation: GA sprays increase bunch size and looseness of grapes.
85. Seedless fruits in tomato and cucumber can be obtained by application of ____________.
A) Auxin
B) Cytokinin
C) ABA
D) Florigen
Answer: A
Explanation: Auxins induce parthenocarpy (fruit development without fertilization).
86. Which hormone promotes senescence (aging) of leaves?
A) Auxin
B) Gibberellin
C) Cytokinin
D) ABA
Answer: D
Explanation: ABA accelerates leaf yellowing and senescence.
87. Which hormone is used as a weed killer in wheat fields?
A) Ethylene
B) 2,4-D (auxin)
C) Cytokinin
D) Gibberellin
Answer: B
Explanation: 2,4-D selectively kills dicot weeds without harming monocot crops.
88. “Richmond Lang Effect” (delay of leaf senescence) is caused by ____________.
A) Auxin
B) Cytokinin
C) Ethylene
D) ABA
Answer: B
Explanation: Cytokinins delay aging, keeping leaves green for longer.
89. Which hormone induces opening of flowers in cotton, tobacco and tomato?
A) Auxin
B) Gibberellin
C) Ethylene
D) Cytokinin
Answer: C
Explanation: Ethylene promotes flower opening in several crops.
90. Apical dominance can be overcome by ____________.
A) Application of gibberellin
B) Application of cytokinin
C) Removal of apical bud
D) Both B and C
Answer: D
Explanation: Apical dominance is controlled by auxin; cytokinin or bud removal releases lateral buds.
91. Which hormone promotes abscission of fruits under stress?
A) Cytokinin
B) ABA
C) Auxin
D) Gibberellin
Answer: B
Explanation: ABA accelerates abscission, especially under drought.
92. Which hormone induces seed germination in barley by activating amylase?
A) Cytokinin
B) Gibberellin
C) Ethylene
D) Auxin
Answer: B
Explanation: GA activates aleurone layer to secrete amylase.
93. Which hormone causes horizontal growth in dark-grown seedlings?
A) Ethylene
B) Auxin
C) Cytokinin
D) ABA
Answer: A
Explanation: Ethylene causes triple response, including horizontal growth.
94. Vivipary (precocious germination in fruits) is due to ____________.
A) High ABA
B) High Ethylene
C) Low ABA & High GA
D) High Auxin
Answer: C
Explanation: In mangroves, reduced ABA and high GA cause seeds to germinate on plant.
95. Which hormone is commercially used to ripen bananas?
A) Auxin
B) Ethylene
C) Cytokinin
D) ABA
Answer: B
Explanation: Ethylene chambers are used to ripen bananas and mangoes.
96. Which hormone enhances resistance against drought by closing stomata?
A) Auxin
B) Ethylene
C) ABA
D) Cytokinin
Answer: C
Explanation: ABA induces stomatal closure to conserve water.
97. Which hormone is used for inducing parthenocarpy in watermelon?
A) Auxin
B) Gibberellin
C) Cytokinin
D) ABA
Answer: B
Explanation: Gibberellin sprays induce seedless fruit development in watermelon.
98. Which hormone promotes xylogenesis (formation of xylem)?
A) Auxin
B) Cytokinin
C) Ethylene
D) ABA
Answer: A
Explanation: Auxins promote differentiation of vascular tissues, especially xylem.
99. Fruit drop in citrus orchards can be controlled by spraying ____________.
A) ABA
B) 2,4-D (auxin)
C) Ethylene
D) Cytokinin
Answer: B
Explanation: Auxin sprays prevent premature fruit abscission.
100. Which is called the “universal growth inhibitor”?
A) Cytokinin
B) ABA
C) Auxin
D) Gibberellin
Answer: B
Explanation: Abscisic acid inhibits growth and is termed the universal growth inhibitor.