🌿 Plant Growth & Development – MCQs

Part 1: Q1–Q25

Q1. Plant growth is best described as

a) Anabolic only
b) Irreversible increase in size
c) Reversible increase in size
d) Only increase in dry weight
Answer: b) Irreversible increase in size
Growth in plants is a permanent (irreversible) increase in size/volume/dry mass due to cell division and enlargement.

Q2. The typical growth curve of a plant organ (e.g., leaf) is

a) Linear
b) Sigmoid (S-shaped)
c) Exponential forever
d) Stepwise
Answer: b) Sigmoid (S-shaped)
Shows lag phase, log (exponential) phase, and stationary phase.

Q3. Primary growth in plants results from activity of

a) Apical meristems
b) Lateral meristems
c) Intercalary meristems
d) Cork cambium only
Answer: a) Apical meristems
Apical meristems at root and shoot tips cause elongation (primary growth).

Q4. Secondary growth in dicot stems is mainly due to

a) Apical meristem
b) Intercalary meristem
c) Vascular cambium and cork cambium
d) Pericycle only
Answer: c) Vascular cambium and cork cambium
They add secondary xylem/phloem and periderm, increasing girth.

Q5. The phase of fast maximum growth in the sigmoid curve is

a) Lag phase
b) Log phase
c) Stationary phase
d) Senescent phase
Answer: b) Log phase
Cells divide and elongate rapidly—maximum growth rate.

Q6. The most abundant natural auxin is

a) 2,4-D
b) IAA (Indole-3-acetic acid)
c) IBA
d) NAA
Answer: b) IAA (Indole-3-acetic acid)
IAA is the principal endogenous auxin in higher plants.

Q7. Polar transport of auxin occurs mainly

a) Non-directionally
b) Basipetally in shoots
c) Acropetally in shoots
d) Only through phloem mass flow
Answer: b) Basipetally in shoots
Auxin moves cell-to-cell, predominantly from apex toward base in shoots.

Q8. Apical dominance is primarily controlled by

a) Cytokinins
b) Auxins from shoot tip
c) Abscisic acid
d) Ethylene
Answer: b) Auxins from shoot tip
Apical auxin suppresses lateral buds; removing the tip releases buds (cytokinins can counter it).

Q9. Which hormone most strongly promotes stem elongation and bolting?

a) ABA
b) Gibberellins (GA)
c) Ethylene
d) Cytokinins
Answer: b) Gibberellins (GA)
GAs stimulate cell elongation, internode extension, and bolting in rosette plants.

Q10. Dwarf pea/maize mutants recover normal height upon treatment with

a) ABA
b) GA₃
c) Ethylene
d) Cytokinin
Answer: b) GA₃
Gibberellin-deficient dwarfs elongate when supplied GA₃.

Q11. Natural cytokinin first discovered in maize kernels is

a) Kinetin
b) Zeatin
c) BAP
d) TDZ
Answer: b) Zeatin
Zeatin is a natural cytokinin from Zea mays.

Q12. Which hormone generally promotes senescence and stomatal closure?

a) Auxin
b) Cytokinin
c) Abscisic acid (ABA)
d) GA₃
Answer: c) Abscisic acid (ABA)
ABA induces stomatal closure under stress and accelerates senescence/dormancy.

Q13. Triple response (in dark-grown seedlings) is characteristic of

a) Auxin
b) Cytokinin
c) Ethylene
d) GA
Answer: c) Ethylene
Ethylene causes reduced elongation, hypocotyl swelling, and apical hook maintenance.

Q14. Fruit ripening in climacteric fruits is hastened by

a) Cytokinin
b) GA
c) Ethylene
d) ABA
Answer: c) Ethylene
Ethylene triggers climacteric rise in respiration and ripening.

Q15. Parthenocarpy (seedless fruit) can be induced most directly by

a) ABA
b) GA or Auxin
c) Cytokinin only
d) Ethylene only
Answer: b) GA or Auxin
Both can stimulate fruit set without fertilization (e.g., GA in grapes).

Q16. Photoperiodism refers to plant response to

a) Light quality only
b) Length of day/night
c) Temperature duration only
d) Light intensity only
Answer: b) Length of day/night
Flowering is controlled by photoperiod—critical day/night length.

Q17. Short-day plants (SDP) flower when

a) Day is longer than a critical value
b) Night is shorter than a critical value
c) Night is longer than a critical value
d) Independent of photoperiod
Answer: c) Night is longer than a critical value
SDPs need long uninterrupted dark period (critical night).

Q18. The photoreceptor mediating photoperiodic flowering is

a) Carotenoid
b) Flavonoid
c) Phytochrome
d) Chlorophyll b
Answer: c) Phytochrome
Phytochrome (Pr/Pfr) perceives red/far-red light affecting flowering.

Q19. Night break (flash of light during dark) in SDPs typically

a) Promotes flowering
b) Inhibits flowering
c) Has no effect
d) Promotes leaf abscission
Answer: b) Inhibits flowering
Interrupting the long night converts it effectively to short night, preventing SDP flowering.

Q20. Vernalization is

a) Requirement of low temperature for flowering
b) Requirement of high temperature for germination
c) Requirement of red light for flowering
d) Response to day length only
Answer: a) Requirement of low temperature for flowering
Cold treatment (e.g., winter cereals) accelerates subsequent flowering.

Q21. Florigen is best described as

a) A specific hormone isolated in pure form
b) A transmissible flowering signal from leaves
c) Root-derived inhibitor
d) Ethylene gas
Answer: b) A transmissible flowering signal from leaves
Now explained largely as FT protein/complex moving from induced leaves to the shoot apex.

Q22. Differentiation, dedifferentiation, redifferentiation respectively mean

a) Loss, gain, and loss of function
b) Maturation, return to meristematic state, and specialization again
c) Only maturation in one direction
d) Only cell enlargement
Answer: b) Maturation, return to meristematic state, and specialization again
E.g., parenchyma dedifferentiates to form cambium; then redifferentiates to xylem/phloem.

Q23. Which tissue gives rise to lateral roots in dicots?

a) Endodermis
b) Pericycle
c) Cortex
d) Epidermis
Answer: b) Pericycle
Lateral roots initiate endogenously from pericycle cells.

Q24. Auxin promotes cell elongation via the

a) Protein denaturation hypothesis
b) Acid-growth hypothesis
c) Oxidative burst hypothesis
d) Starch-statolith hypothesis
Answer: b) Acid-growth hypothesis
Auxin activates proton pumps → cell wall acidification → expansins loosen wall → elongation.

Q25. Which pair is correctly matched?

a) 2,4-D – rooting in cuttings
b) NAA – herbicide in cereals
c) Ethrel – releases ethylene for ripening
d) Cytokinin – promotes abscission
Answer: c) Ethrel – releases ethylene for ripening
Ethrel (ethephon) decomposes to ethylene; 2,4-D is mainly a selective herbicide; NAA commonly aids rooting; cytokinins generally delay abscission/senescence.

🌱 Plant Physiology – Plant Growth and Development

📘 Part 2: MCQs (Q26–Q50)

Q26. Which type of growth is exhibited by plant roots and shoots?

a) Determinate growth
b) Indeterminate growth
c) Apical-basal growth
d) Limited growth

Answer: b) Indeterminate growth

a) Wrong – determinate growth stops after a certain point.
b) Correct – roots and shoots continue to grow throughout life.
c) Wrong – apical-basal refers to direction, not continuity.
d) Wrong – limited growth applies to some plant organs, not roots/shoots.

Q27. The sigmoid growth curve in plants is also called:

a) J-shaped curve
b) S-shaped curve
c) Linear curve
d) Exponential curve

Answer: b) S-shaped curve

a) Wrong – J-shape indicates unrestricted exponential growth.
b) Correct – plant growth generally follows an S-curve (lag, log, stationary phases).
c) Wrong – linear growth is straight-line increase.
d) Wrong – exponential is only one phase, not the entire pattern.

Q28. Which hormone promotes cell elongation?

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

Answer: a) Auxin

a) Correct – auxins stimulate elongation of cells in shoots.
b) Wrong – cytokinins promote cell division.
c) Wrong – ABA inhibits growth.
d) Wrong – ethylene mainly promotes fruit ripening and abscission.

Q29. Gibberellins were first discovered from:

a) Wheat
b) Rice
c) Maize
d) Pea

Answer: b) Rice

a) Wrong – wheat is affected by GA but not the discovery source.
b) Correct – discovered from “foolish seedling” disease in rice caused by Gibberella fujikuroi.
c) Wrong – maize was later used for GA studies.
d) Wrong – pea was for auxin studies.

Q30. Which hormone breaks seed dormancy?

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

Answer: c) Gibberellin

a) Wrong – ABA induces dormancy.
b) Wrong – ethylene helps in fruit ripening, not dormancy breaking.
c) Correct – GA breaks seed dormancy and promotes germination.
d) Wrong – cytokinins promote cell division, not germination.

Q31. Which photoreceptor controls photoperiodism?

a) Chlorophyll
b) Phytochrome
c) Carotenoids
d) Xanthophyll

Answer: b) Phytochrome

a) Wrong – chlorophyll is for photosynthesis.
b) Correct – phytochrome senses red and far-red light, controlling flowering.
c) Wrong – carotenoids are accessory pigments.
d) Wrong – xanthophyll helps in photoprotection.

Q32. Vernalization is:

a) Promotion of flowering by high temperature
b) Promotion of flowering by low temperature
c) Dormancy due to light
d) Growth by auxins

Answer: b) Promotion of flowering by low temperature

a) Wrong – high temp is not vernalization.
b) Correct – exposure to low temperature promotes flowering in biennials and winter crops.
c) Wrong – photoperiodism, not vernalization.
d) Wrong – auxins are unrelated to vernalization.

Q33. Bolting in rosette plants is induced by:

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

Answer: b) Gibberellin

a) Wrong – auxins elongate but don’t cause bolting.
b) Correct – GA causes sudden elongation (bolting) in rosette plants like cabbage.
c) Wrong – cytokinins promote cell division, not bolting.
d) Wrong – ABA inhibits growth.

Q34. Which hormone is also called “stress hormone”?

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

Answer: c) ABA

a) Wrong – cytokinins promote growth, not stress.
b) Wrong – ethylene regulates ripening.
c) Correct – abscisic acid induces dormancy and closes stomata under stress.
d) Wrong – auxins regulate elongation and tropisms.

Q35. The phase of maximum growth in the sigmoid curve is:

a) Lag phase
b) Log phase
c) Stationary phase
d) Decline phase

Answer: b) Log phase

a) Wrong – lag phase is initial slow growth.
b) Correct – log phase is rapid, exponential growth.
c) Wrong – stationary phase is equilibrium.
d) Wrong – decline is rarely used in plant growth curves.

Q36. The term “apical dominance” is associated with:

a) Gibberellins
b) Cytokinins
c) Auxins
d) Ethylene

Answer: c) Auxins

a) Wrong – gibberellins induce elongation but not apical dominance.
b) Wrong – cytokinins promote lateral bud growth.
c) Correct – auxin from shoot apex suppresses lateral buds.
d) Wrong – ethylene causes abscission.

Q37. The climacteric rise in respiration is associated with:

a) Seed germination
b) Flowering
c) Fruit ripening
d) Leaf abscission

Answer: c) Fruit ripening

a) Wrong – germination doesn’t involve climacteric rise.
b) Wrong – flowering is light/temperature regulated.
c) Correct – respiration rate increases during fruit ripening (ethylene-controlled).
d) Wrong – abscission isn’t linked to climacteric rise.

Q38. Short-day plants require:

a) Day length longer than critical photoperiod
b) Day length shorter than critical photoperiod
c) No photoperiod
d) Continuous darkness

Answer: b) Day length shorter than critical photoperiod

a) Wrong – that’s long-day plants.
b) Correct – short-day plants (e.g., rice) flower when day length is shorter.
c) Wrong – photoperiod is essential.
d) Wrong – continuous darkness prevents flowering.

Q39. Cytokinins are mostly synthesized in:

a) Leaves
b) Shoot apex
c) Root apex
d) Flowers

Answer: c) Root apex

a) Wrong – leaves are not primary cytokinin sources.
b) Wrong – shoot apex responds to cytokinins.
c) Correct – cytokinins are synthesized in root tips and transported upward.
d) Wrong – flowers are not major cytokinin sources.

Q40. Which plant hormone induces parthenocarpy?

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

Answer: a) Auxin

a) Correct – auxins induce fruit development without fertilization.
b) Wrong – ABA inhibits growth.
c) Wrong – cytokinins don’t induce parthenocarpy.
d) Wrong – ethylene regulates ripening, not parthenocarpy.

Q41. Which process is promoted by ethylene?

a) Stem elongation
b) Leaf abscission
c) Seed dormancy
d) Root elongation

Answer: b) Leaf abscission

a) Wrong – gibberellins elongate stems.
b) Correct – ethylene accelerates leaf abscission and fruit drop.
c) Wrong – ABA induces dormancy.
d) Wrong – auxins stimulate root elongation.

Q42. Which hormone promotes stomatal closure during water stress?

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

Answer: c) ABA

a) Wrong – auxins regulate elongation.
b) Wrong – cytokinins delay senescence, not stomatal closure.
c) Correct – ABA signals guard cells to close stomata in drought.
d) Wrong – ethylene promotes ripening.

Q43. Phototropism is caused mainly by:

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

Answer: c) Auxin

a) Wrong – cytokinins aren’t light-sensitive.
b) Wrong – gibberellins elongate stems.
c) Correct – auxins accumulate on the shaded side, causing bending.
d) Wrong – ABA inhibits growth.

Q44. Which hormone delays leaf senescence?

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

Answer: b) Cytokinin

a) Wrong – ethylene promotes senescence.
b) Correct – cytokinins delay senescence (“Richmond Lang Effect”).
c) Wrong – ABA accelerates senescence.
d) Wrong – auxins don’t directly affect senescence.

Q45. A long-day plant flowers when:

a) Day is longer than critical photoperiod
b) Day is shorter than critical photoperiod
c) There is no light
d) Exposed to continuous darkness

Answer: a) Day is longer than critical photoperiod

a) Correct – long-day plants (wheat, barley) need longer days.
b) Wrong – that’s short-day plants.
c) Wrong – some light is required.
d) Wrong – continuous darkness prevents flowering.

Q46. “Foolish seedling disease” is due to:

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

Answer: c) Gibberellin

a) Wrong – ABA causes dormancy, not elongation.
b) Wrong – ethylene causes ripening.
c) Correct – excessive GA secretion leads to abnormal elongation in rice.
d) Wrong – cytokinins stimulate division, not elongation.

Q47. Which process does NOT require gibberellins?

a) Bolting
b) Fruit ripening
c) Breaking dormancy
d) Stem elongation

Answer: b) Fruit ripening

a) Wrong – GA induces bolting.
b) Correct – ethylene controls ripening, not GA.
c) Wrong – GA breaks dormancy.
d) Wrong – GA elongates stems.

Q48. Growth in length is primarily due to:

a) Apical meristem
b) Lateral meristem
c) Intercalary meristem
d) Cork cambium

Answer: a) Apical meristem

a) Correct – apical meristems produce primary growth in length.
b) Wrong – lateral meristems increase thickness.
c) Wrong – intercalary meristem helps regrowth (e.g., grasses).
d) Wrong – cork cambium produces protective periderm.

Q49. Which hormone promotes flowering in pineapple?

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

Answer: b) Ethylene

a) Wrong – auxins don’t induce pineapple flowering.
b) Correct – ethylene induces flowering in pineapple.
c) Wrong – cytokinins are not flowering signals.
d) Wrong – gibberellins induce flowering in long-day plants, not pineapple.

Q50. Triple response of ethylene includes all EXCEPT:

a) Inhibition of stem elongation
b) Promotion of lateral expansion
c) Horizontal growth of stem
d) Increased apical dominance

Answer: d) Increased apical dominance

a) Correct – ethylene inhibits elongation.
b) Correct – ethylene promotes lateral expansion.
c) Correct – ethylene causes horizontal growth.
d) Wrong – apical dominance is caused by auxins, not ethylene.

🌱 Plant Growth and Development MCQs (Part 3: Q51–Q75)

Q51. Which hormone is primarily responsible for apical dominance in plants?

a) Auxin
b) Cytokinin
c) Gibberellin
d) Abscisic acid

✅ Answer: a) Auxin

Auxin promotes apical dominance by suppressing lateral bud growth.
Cytokinin promotes lateral bud growth.
Gibberellin helps in stem elongation.
Abscisic acid is a growth inhibitor.

Q52. Bolting in rosette plants is induced by:

a) Auxins
b) Gibberellins
c) Cytokinins
d) Ethylene

✅ Answer: b) Gibberellins

Gibberellins stimulate stem elongation in rosette plants (bolting).
Auxins mainly elongate cells.
Cytokinins promote cell division.
Ethylene induces fruit ripening.

Q53. Which hormone delays senescence of leaves and fruits?

a) Auxin
b) Cytokinin
c) Ethylene
d) Abscisic acid

✅ Answer: b) Cytokinin

Cytokinins delay senescence (anti-aging hormone).
Auxins prevent leaf abscission but not senescence.
Ethylene accelerates senescence.
Abscisic acid promotes dormancy and senescence.

Q54. Photoperiodism is best defined as:

a) Response to gravity
b) Response to light duration
c) Response to temperature
d) Response to water

✅ Answer: b) Response to light duration

Photoperiodism is the response of plants to light/dark duration, controlling flowering.
Gravity → geotropism.
Temperature → vernalization.
Water → hydrotropism.

Q55. A short-day plant requires:

a) More light than critical day length
b) Less light than critical day length
c) Continuous light
d) Only red light

✅ Answer: b) Less light than critical day length

Short-day plants flower when light duration is less than a critical day length.
Long-day plants need more light.
Continuous light inhibits some plants.
Red light affects photoperiodism, but it’s not the only requirement.

Q56. Vernalization refers to:

a) Response to light period
b) Response to gravity
c) Induction of flowering by low temperature
d) Breaking seed dormancy by water

✅ Answer: c) Induction of flowering by low temperature

Vernalization is flowering induced by low temperature.
Light response = photoperiodism.
Gravity response = geotropism.
Water response = hydration.

Q57. Phytochrome exists in two interconvertible forms:

a) P660 and P730
b) Pr and Pfr
c) Chlorophyll a and b
d) NADH and NADPH

✅ Answer: b) Pr and Pfr

Phytochrome exists as Pr (absorbs red light ~660 nm) and Pfr (absorbs far-red light ~730 nm).
Pfr is the biologically active form.
Chlorophylls are pigments.
NADH/NADPH are electron carriers.

Q58. Ethylene is a unique hormone because it is:

a) Water-soluble
b) Gaseous
c) Insoluble in lipids
d) Produced only in roots

✅ Answer: b) Gaseous

Ethylene is a gaseous plant hormone regulating ripening.
Other hormones are non-gaseous.
It is soluble in lipids, diffusing easily.
Produced in various parts (not just roots).

Q59. The triple response of ethylene includes:

a) Elongation, apical dominance, flowering
b) Inhibition of elongation, swelling, horizontal growth
c) Senescence, dormancy, abscission
d) Photosynthesis, respiration, transpiration

✅ Answer: b) Inhibition of elongation, swelling, horizontal growth

Ethylene reduces elongation, thickens stem, and promotes horizontal growth (triple response).

Q60. Which hormone promotes abscission of leaves and fruits?

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

✅ Answer: c) Ethylene

Ethylene accelerates abscission (shedding).
Auxins actually delay abscission.
Cytokinins and gibberellins do not directly induce abscission.

Q61. Which plant hormone is stress-induced and promotes seed dormancy?

a) Cytokinin
b) Gibberellin
c) Abscisic acid
d) Auxin

✅ Answer: c) Abscisic acid

Abscisic acid (ABA) promotes seed dormancy and stress resistance.
Cytokinins promote growth.
Gibberellins break dormancy.
Auxins regulate elongation.

Q62. Apical dominance can be overcome by:

a) Removing lateral buds
b) Removing apical bud
c) Application of auxin
d) Application of gibberellin

✅ Answer: b) Removing apical bud

Removal of the apical bud reduces auxin, allowing lateral buds to grow.

Q63. Which hormone promotes parthenocarpy (seedless fruit formation)?

a) Ethylene
b) Auxin
c) Abscisic acid
d) Cytokinin

✅ Answer: b) Auxin

Auxin promotes parthenocarpic fruit formation.
Ethylene also can induce parthenocarpy in some cases.
ABA inhibits growth.
Cytokinins promote cell division.

Q64. Which process is associated with scarlet coloration in tomato fruit ripening?

a) Accumulation of anthocyanins
b) Breakdown of chlorophyll and synthesis of lycopene
c) Synthesis of carotenoids and xanthophylls
d) Conversion of starch into sugar

✅ Answer: b) Breakdown of chlorophyll and synthesis of lycopene

Ethylene induces lycopene synthesis, giving red color.

Q65. Cytokinins were first discovered in:

a) Tobacco pith culture
b) Maize endosperm
c) Coconut milk
d) DNA hydrolysate

✅ Answer: d) DNA hydrolysate

Cytokinins were first found in herring sperm DNA hydrolysate as kinetin.

Q66. The main site of auxin production is:

a) Mature leaves
b) Root tip
c) Shoot tip
d) Cambium

✅ Answer: c) Shoot tip

Shoot tips are the main site of auxin synthesis.
Root tips also produce some auxin but at lower levels.

Q67. Florigen is hypothesized as:

a) Gibberellin
b) Cytokinin
c) A flowering hormone
d) Abscisic acid

✅ Answer: c) A flowering hormone

Florigen is a hypothetical flowering hormone produced in leaves under favorable photoperiod.

Q68. The red/far-red light response in flowering is mediated by:

a) Chlorophyll
b) Carotenoid
c) Phytochrome
d) Anthocyanin

✅ Answer: c) Phytochrome

Phytochrome detects red/far-red light, regulating photoperiodism.

Q69. Which hormone is also known as “stress hormone” in plants?

a) Auxin
b) Gibberellin
c) Abscisic acid
d) Ethylene

✅ Answer: c) Abscisic acid

ABA is called stress hormone, regulating drought tolerance and dormancy.

Q70. In short-day plants, interruption of dark period by red light:

a) Promotes flowering
b) Inhibits flowering
c) Has no effect
d) Promotes leaf senescence

✅ Answer: b) Inhibits flowering

Short-day plants require long dark periods; interruption by red light inhibits flowering.

Q71. Which plant hormone promotes seed germination by breaking dormancy?

a) Auxin
b) Gibberellin
c) Cytokinin
d) Abscisic acid

✅ Answer: b) Gibberellin

Gibberellins break dormancy and promote germination.
ABA maintains dormancy.

Q72. Which hormone promotes cell wall loosening, enabling cell elongation?

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

✅ Answer: c) Auxin

Auxin promotes elongation by loosening cell walls.

Q73. Which hormone is associated with fruit ripening and sweetening?

a) Auxin
b) Ethylene
c) Gibberellin
d) Abscisic acid

✅ Answer: b) Ethylene

Ethylene promotes ripening, starch-to-sugar conversion, and color change.

Q74. Which plant hormone inhibits seed germination under stress conditions?

a) Auxin
b) Gibberellin
c) Cytokinin
d) Abscisic acid

✅ Answer: d) Abscisic acid

ABA prevents germination under unfavorable conditions.

Q75. Which hormone promotes female flowers in cucumber?

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

✅ Answer: a) Ethylene

Ethylene promotes femaleness in cucurbits, while gibberellins promote maleness.

🌱 Plant Growth and Development MCQs Part 4: MCQs (Q76 – Q100)

Q76. Which of the following hormones promotes cell elongation in plants?
a) Cytokinin
b) Auxin ✅
c) Abscisic acid
d) Ethylene

Answer: b) Auxin

Auxin promotes cell elongation by loosening the cell wall.
Cytokinins promote cell division.
ABA inhibits growth.
Ethylene promotes fruit ripening and abscission.

Q77. Vernalization helps in:
a) Seed germination
b) Breaking seed dormancy
c) Flowering ✅
d) Cell division

Answer: c) Flowering

Vernalization is exposure to low temperature to promote flowering in biennials and winter crops.

Q78. Which plant hormone is known as the “stress hormone”?
a) Auxin
b) Cytokinin
c) Abscisic acid ✅
d) Gibberellin

Answer: c) Abscisic acid

ABA induces dormancy, closes stomata during stress, and inhibits growth.

Q79. Which is the site of perception of photoperiod in plants?
a) Leaves ✅
b) Flowers
c) Roots
d) Stem

Answer: a) Leaves

Leaves perceive light/dark cycles, and the signal is transmitted to induce flowering.

Q80. Gibberellins were first discovered in:
a) Maize
b) Rice seedlings
c) Fungus Gibberella fujikuroi ✅
d) Pea plants

Answer: c) Gibberella fujikuroi

It caused “Bakanae” disease in rice seedlings, leading to discovery of gibberellins.

Q81. Which hormone promotes fruit ripening?
a) Ethylene ✅
b) Cytokinin
c) Gibberellin
d) Auxin

Answer: a) Ethylene

Ethylene accelerates fruit ripening by increasing respiration and softening tissues.

Q82. Apical dominance in plants is caused by:
a) Cytokinin
b) Auxin ✅
c) ABA
d) Gibberellin

Answer: b) Auxin

Auxin produced in the apical bud inhibits growth of lateral buds (apical dominance).

Q83. Which process is influenced by phytochrome pigment?
a) Phototropism
b) Photoperiodism ✅
c) Apical dominance
d) Water absorption

Answer: b) Photoperiodism

Phytochrome is a light-sensitive pigment regulating flowering by detecting light/dark periods.

Q84. Which hormone is responsible for seed dormancy?
a) Gibberellin
b) Auxin
c) Abscisic acid ✅
d) Cytokinin

Answer: c) Abscisic acid

ABA induces and maintains seed dormancy, preventing premature germination.

Q85. Which type of movement is shown by the opening of stomata?
a) Growth movement
b) Nastic movement
c) Turgor movement ✅
d) Tropic movement

Answer: c) Turgor movement

Stomatal opening and closing depend on turgor changes in guard cells.

Q86. Scarification is the process of:
a) Exposing seeds to cold temperature
b) Removing seed coat mechanically ✅
c) Breaking dormancy by light
d) Application of gibberellins

Answer: b) Removing seed coat mechanically

Scarification weakens or removes hard seed coats to break physical dormancy.

Q87. Which hormone promotes leaf senescence?
a) Cytokinin
b) Auxin
c) Ethylene ✅
d) Gibberellin

Answer: c) Ethylene

Ethylene accelerates leaf senescence and abscission. Cytokinin delays senescence.

Q88. The conversion of vegetative apex into floral meristem is regulated by:
a) Photoperiod ✅
b) Auxin
c) Ethylene
d) Cytokinin

Answer: a) Photoperiod

Flowering is induced by specific light/dark periods sensed by leaves.

Q89. Which hormone is also called the “feminizing hormone” in plants?
a) Cytokinin
b) Ethylene ✅
c) Gibberellin
d) Auxin

Answer: b) Ethylene

Ethylene induces femaleness in cucurbits and other plants.

Q90. Bolting in onion is caused by:
a) Auxin
b) Cytokinin
c) Gibberellin ✅
d) ABA

Answer: c) Gibberellin

Gibberellins induce bolting (sudden elongation of internodes) in rosette plants like onion.

Q91. Which plant hormone promotes parthenocarpy (fruit without fertilization)?
a) Gibberellin ✅
b) ABA
c) Cytokinin
d) Ethylene

Answer: a) Gibberellin

Gibberellins induce seedless fruit development without fertilization.

Q92. Red light promotes flowering in:
a) Long-day plants ✅
b) Short-day plants
c) Day-neutral plants
d) None of these

Answer: a) Long-day plants

Red light exposure promotes flowering in long-day plants.

Q93. Which hormone delays leaf senescence?
a) Ethylene
b) ABA
c) Cytokinin ✅
d) Auxin

Answer: c) Cytokinin

Cytokinin promotes nutrient mobilization and delays leaf aging (anti-senescence effect).

Q94. Phototropism in plants is mainly due to:
a) Gibberellin
b) Auxin ✅
c) Cytokinin
d) ABA

Answer: b) Auxin

Auxin accumulates on the shaded side, promoting elongation and bending towards light.

Q95. Which factor breaks seed dormancy in lettuce?
a) Red light ✅
b) Darkness
c) Cold temperature
d) Scarification

Answer: a) Red light

In lettuce seeds, red light activates phytochrome to break dormancy and initiate germination.

Q96. Which hormone is used to delay ripening of fruits during transport?
a) Ethylene
b) Auxin
c) Cytokinin
d) Abscisic acid ✅

Answer: d) Abscisic acid

ABA and ethylene inhibitors are used to delay ripening for storage and transport.

Q97. Apical dominance can be overcome by:
a) Removing apical bud ✅
b) Applying auxin
c) Applying ABA
d) Applying ethylene

Answer: a) Removing apical bud

Decapitating the apex removes auxin influence, allowing lateral buds to grow.

Q98. Which hormone promotes flowering in pineapple?
a) Auxin
b) Ethylene ✅
c) Gibberellin
d) ABA

Answer: b) Ethylene

Ethylene promotes synchronous flowering in pineapple plants.

Q99. Which of the following is an example of a long-day plant?
a) Rice
b) Pea ✅
c) Tobacco
d) Cotton

Answer: b) Pea

Pea, wheat, and barley are long-day plants. Rice and tobacco are short-day plants.

Q100. Abscisic acid is also called:
a) Ripening hormone
b) Dormin ✅
c) Antiauxin
d) Florigen

Answer: b) Dormin

ABA is called Dormin because it induces dormancy in seeds and buds.

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