1. The first discovered plant hormone is:
A) Gibberellin
B) Cytokinin
C) Auxin
D) Abscisic acid
Answer: C) Auxin
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) Charles Darwin
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) Frits Went
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) Indole-3-acetic acid (IAA)
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) IBA
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) NAA
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) Shoot tips
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) Apical dominance
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) Decapitation
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) 2,4-D
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) Auxin
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) Auxin
Explanation: Auxins induce fruit formation without fertilization.
13. Which hormone delays leaf abscission?
A) ABA
B) Ethylene
C) Auxin
D) Cytokinin
Answer: C) Auxin
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) Root initiation
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) NAA
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) Phototropism
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) Lower side
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) Inhibition of elongation
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) NAA
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) Oat coleoptile
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) IAA
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) Secondary growth
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) Increasing cell wall plasticity
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) Parthenocarpy
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) Leaf abscission
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) Rice seedlings
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) Kurosawa
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) Stem elongation
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) Gibberellin
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) Gibberellin
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) Low temperature
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) Gibberellin
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) Gibberellin
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) GA₃
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) Grapes
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) Zeatin
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) Miller
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) Kinetin
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) Cell division
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) Shoot formation
Explanation: Cytokinins promote shoot differentiation, whereas auxins promote roots.
41. Cytokinins delay:
A) Senescence
B) Flowering
C) Apical dominance
D) Dormancy
Answer: A) Senescence
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) Zeatin
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) Root tips
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) Cytokinin
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) Auxins
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) Cytokinin
Explanation: Cytokinins delay senescence and extend freshness of vegetables.
47. Coconut milk contains:
A) Auxins
B) Cytokinins
C) Gibberellins
D) Ethylene
Answer: B) Cytokinins
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) Root formation
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) Purine (adenine)
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) Auxin & Cytokinin
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) Ethylene
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) Ethylene
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) Flowering in pineapple
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) Ethylene
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) Senescence and abscission
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) Ethylene
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) All of these
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) Inhibition of elongation, stem swelling, horizontal growth
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) Ripening fruits
Explanation: Climacteric fruits produce maximum ethylene during ripening.
60. Ethylene is commercially available as:
A) IAA
B) NAA
C) Ethrel
D) Zeatin
Answer: C) Ethrel
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) Cucurbits
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) Respiration
Explanation: Ethylene increases respiration during fruit ripening.
63. Ethylene delays:
A) Abscission
B) Senescence
C) Flowering
D) None of these
Answer: D) None of these
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) Abscisic acid
Explanation: ABA accumulates under stress (drought, cold, salinity).
65. Abscisic acid was initially called:
A) Kinetin
B) Dormin
C) Zeatin
D) Florigen
Answer: B) Dormin
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) Abscisic acid
Explanation: ABA prevents water loss by closing stomata.
67. ABA is antagonistic to:
A) Auxin
B) Gibberellin
C) Cytokinin
D) Ethylene
Answer: B) Gibberellin
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) Root cap and mature leaves
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) ABA
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) ABA
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) Abscisic acid
Explanation: ABA accelerates senescence and abscission.
72. ABA plays a major role in:
A) Senescence
B) Flowering
C) Fruit ripening
D) Phototropism
Answer: A) Senescence
Explanation: ABA induces leaf aging and death.
73. ABA inhibits:
A) Fruit ripening
B) Stomatal closure
C) Senescence
D) Dormancy
Answer: A) Fruit ripening
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) Both B and C
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) Abscisic acid
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) Ethylene
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) Gibberellin
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) Gibberellin & ABA
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) Ratio of cytokinin to auxin
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) Flowering
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) High cytokinin, low auxin
Explanation: Cytokinins promote shoot development.
82. Which hormone promotes femaleness in cucumber flowers?
A) Auxin
B) Gibberellin
C) Ethylene
D) Cytokinin
Answer: C) Ethylene
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) Gibberellin
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) Gibberellin
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) Auxin
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) ABA
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) 2,4-D (auxin)
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) Cytokinin
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) Ethylene
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) Both B and C
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) ABA
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) Gibberellin
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) Ethylene
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) Low ABA & High GA
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) Ethylene
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) ABA
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) Gibberellin
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) Auxin
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) 2,4-D (auxin)
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) ABA
Explanation: Abscisic acid inhibits growth and is termed the universal growth inhibitor.