Plant Growth and Development — Practice Questions with Answers
30 free MCQs on Plant Growth and Development with worked answers and explanations. Phases of plant growth, the five classical plant hormones plus newer ones, photoperiodism, vernalization, and seed dormancy.
Below are 30 practice questions on Plant Growth and Development, sorted Easy → Hard. Tap “Show answer & explanation” under any question to check yourself. Want the full theory first? Read the Plant Growth and Development notes.
Geometric growth (where both daughter cells keep dividing) produces this classic S-shaped curve: a slow lag phase, a rapid exponential phase, and a levelling-off stationary phase as nutrients or space become limiting — the same fundamental pattern seen in population growth.
Easy — 10 questions
Q1.
Gibberellins promote:
A Adventitious root initiation exclusively, with no effect on shoot tissue
B Stomatal closure via guard cell turgor loss under water stress
C Stem elongation and seed germination
D Climacteric fruit ripening through ethylene biosynthesis induction
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Answer: C. Stem elongation and seed germination
Why: Gibberellins promote stem elongation (important in dwarf plants), seed germination, and flowering in some plants.
Q2.
Auxin promotes:
A Cell elongation and phototropism
B Cell division at root tip
C Leaf senescence
D Stomatal closure
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Answer: A. Cell elongation and phototropism
Why: Auxin (IAA) promotes cell elongation in stems and is responsible for phototropism (bending toward light).
Q3.
Ethylene is a plant hormone involved in:
A Stem elongation driven by cell wall loosening at the apical meristem
B Fruit ripening and abscission
C Adventitious root formation at the cut ends of stem cuttings
D Directional bending of shoots toward a unidirectional light source
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Answer: B. Fruit ripening and abscission
Why: Ethylene is a gaseous hormone. It promotes fruit ripening and abscission (leaf/fruit drop).
Q4.
ABA (Abscisic acid) causes:
A Rapid stem elongation and internode growth
B Triggering of seed germination processes
C Stomatal closure and dormancy
D Acceleration of fruit ripening and softening
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Answer: C. Stomatal closure and dormancy
Why: ABA is a stress hormone. It causes stomatal closure (water stress) and promotes seed/bud dormancy. Known as stress hormone.
Q5.
Apical dominance in plants is regulated by:
A Gibberellins diffusing downward from the shoot apex to suppress lateral buds
B Cytokinins transported upward from the root tip through the xylem stream
C Auxin (IAA) from apical bud
D Ethylene accumulating locally at axillary bud junctions
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Answer: C. Auxin (IAA) from apical bud
Why: Auxin produced by the apical bud inhibits growth of lateral buds (apical dominance). Removing the apex allows lateral growth.
Q6.
Cytokinins, a class of plant hormones, mainly promote:
A Stomatal closure
B Stem elongation
C Cell division
D Fruit ripening
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Answer: C. Cell division
Why: Cytokinins primarily promote cell division (cytokinesis) and also help delay senescence and promote lateral bud growth in plants.
Q7.
Which plant hormone is commonly associated with promoting fruit ripening?
A Ethylene
B Gibberellin
C Auxin
D Cytokinin
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Answer: A. Ethylene
Why: Ethylene, a gaseous plant hormone, is well known for promoting fruit ripening as well as causing leaf senescence and abscission.
Q8.
The bending of a plant shoot toward light is an example of:
A Geotropism
B Thigmotropism
C Hydrotropism
D Phototropism
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Answer: D. Phototropism
Why: Phototropism is the directional growth response of a plant organ toward or away from a light source, with shoots typically showing positive phototropism.
Q9.
Seed dormancy in many plants helps ensure that:
A Seeds germinate immediately after dispersal regardless of conditions
B Germination occurs only under favourable environmental conditions
C Germination always requires artificial chemical treatment
D Seeds lose viability shortly after they are formed
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Answer: B. Germination occurs only under favourable environmental conditions
Why: Seed dormancy is a resting period that prevents germination until environmental conditions such as moisture, temperature, and light become favourable for seedling survival.
Q10.
Differentiation in plant development refers to the process by which:
A Mature cells revert back to a dividing meristematic state
B Cells derived from meristems mature to perform specific functions
C Plant organs increase only in number, not in specialization
D Cells divide repeatedly without any change in structure
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Answer: B. Cells derived from meristems mature to perform specific functions
Why: Differentiation is the process by which cells produced by meristems undergo structural and functional changes to become specialized for a particular role, such as forming xylem or phloem.
Medium — 10 questions
Q11.
Vernalization is:
A A plant's photoperiodic response to the relative length of day versus night
B Requirement for cold treatment to induce flowering
C Application of elevated temperature treatment to accelerate vegetative growth
D Prolonged exposure to drought stress that triggers stomatal closure
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Answer: B. Requirement for cold treatment to induce flowering
Why: Vernalization: plants require prolonged cold treatment (winter) to acquire the ability to flower in spring. Promotes flowering in wheat, barley.
Q12.
Cytokinin promotes:
A Stem elongation by loosening cell walls at the subapical meristem
B Cell division and delays senescence
C Climacteric fruit ripening coupled with ethylene release
D Primary root elongation exclusively, with no effect on lateral shoots
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Answer: B. Cell division and delays senescence
Why: Cytokinins promote cell division, prevent senescence (aging), and promote lateral bud growth. They work together with auxins.
Q13.
Senescence in leaves is triggered by:
A A sharp rise in cytokinin levels delivered from the root system
B Decreased auxin and increased ethylene and ABA
C An isolated drop in ambient temperature unaccompanied by hormonal change
D An increase in available soil water supply to the root system
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Answer: B. Decreased auxin and increased ethylene and ABA
Why: Leaf senescence: triggered by decrease in auxin/cytokinin and increase in ethylene and ABA. Chlorophyll breaks down, nutrients are reclaimed.
Q14.
Phytochrome is a photoreceptor that responds to:
A Blue light exclusively, detected through a flavin chromophore
B Red and far-red light (Pr and Pfr forms)
C Ultraviolet light absorbed by UVR8 photoreceptor proteins
D Green light wavelengths absorbed by chlorophyll-associated pigments
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Answer: B. Red and far-red light (Pr and Pfr forms)
Why: Phytochrome exists as Pr (absorbs red 660 nm, inactive) and Pfr (absorbs far-red 730 nm, active). Controls germination, flowering, shade avoidance.
Q15.
Photoperiodism refers to:
A The overall rate of carbon fixation occurring during daylight hours
B Response of plants to the relative lengths of day and night for flowering
C Light-induced changes in chlorophyll concentration affecting leaf color
D Rapid guard cell turgor changes that open stomata at sunrise
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Answer: B. Response of plants to the relative lengths of day and night for flowering
Why: Photoperiodism: flowering controlled by relative length of dark period (night). Plants classified as short-day, long-day, or day-neutral.
Q16.
Auxin transport is primarily:
A Acropetal, moving upward from the root tip toward the shoot apex
B Polar (from shoot apex downward, basipetal)
C Non-directional, diffusing randomly through ground tissue without polarity
D Confined entirely to root tissue, absent from the shoot system
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Answer: B. Polar (from shoot apex downward, basipetal)
Why: Auxin has polar (unidirectional) transport: basipetal (away from apex, downward in shoots) via PIN efflux carrier proteins.
Q17.
Gravitropism in roots is caused by:
A Auxin accumulating on the upper side, accelerating elongation there instead
B Auxin accumulating on the lower side, inhibiting root elongation there
C Uniform auxin distribution across the root cap with no lateral asymmetry
D Cytokinin redistribution within statocytes sensing the gravity vector
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Answer: B. Auxin accumulating on the lower side, inhibiting root elongation there
Why: In roots, statoliths (starch grains) settle by gravity, signaling asymmetric auxin distribution. Auxin accumulates on lower side, inhibiting growth there, so root curves downward.
Q18.
Apical dominance, in which a growing apical bud suppresses the growth of lateral buds, is mainly caused by:
A Ethylene released from leaves undergoing senescence
B Gibberellin transported upward from the root system
C High auxin levels produced by the apical bud itself
D Cytokinin moving downward from the shoot tip
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Answer: C. High auxin levels produced by the apical bud itself
Why: Auxin produced by the actively growing apical bud moves downward and suppresses the growth of lateral (axillary) buds, a phenomenon called apical dominance.
Q19.
Abscisic acid is often referred to as a stress hormone in plants because it:
A Induces stomatal closure and seed dormancy under stress like drought
B Stimulates internode elongation within the stem under usual circumstances
C Promotes faster cell division in favourable conditions as generally observed
D Speeds up fruit ripening together with ethylene in typical laboratory settings
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Answer: A. Induces stomatal closure and seed dormancy under stress like drought
Why: Abscisic acid (ABA) is associated with plant stress responses; it promotes stomatal closure during water stress and induces seed and bud dormancy, generally acting as a growth inhibitor.
Q20.
Ethylene's effect in promoting fruit ripening is widely exploited commercially because it:
A Promotes ongoing vegetative growth of the fruit as widely reported
B Stops sugar formation within the ripening fruit according to most studies
C Triggers starch-to-sugar conversion and softening of fruit tissue
D Halts respiration within the ripening fruit cells in the majority of documented cases
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Answer: C. Triggers starch-to-sugar conversion and softening of fruit tissue
Why: Ethylene gas triggers ripening-associated changes such as conversion of starch to sugars, breakdown of cell wall components causing softening, and changes in fruit colour, making it useful for controlled ripening.
Hard — 10 questions
Q21.
Florigen is now identified as:
A A specialized auxin derivative synthesized directly within the shoot apical meristem region
B FT protein (Flowering Locus T) produced in leaves, transported to shoot apex via phloem
C Gibberellin A3 synthesized locally within developing floral primordia tissue
D A cytokinin variant transported acropetally upward from the root system below
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Answer: B. FT protein (Flowering Locus T) produced in leaves, transported to shoot apex via phloem
Why: Florigen = FT (Flowering Locus T) protein. Produced in leaf phloem companion cells under inductive photoperiods, transported to shoot apical meristem where it activates flowering genes.
Q22.
Jasmonates (jasmonic acid) are plant hormones that:
A Promote climacteric fruit ripening mainly through ethylene synergism during late development according to standard textbooks
B Activate defense responses against herbivory and pathogens, regulate pollen development, and inhibit growth
C Promote stomatal opening by activating proton pumps within guard cell membranes directly in general practice
D Bind the same TIR1 receptor as auxin and trigger largely identical downstream signaling pathways as frequently described
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Answer: B. Activate defense responses against herbivory and pathogens, regulate pollen development, and inhibit growth
Why: Jasmonate (JA-Ile): key mediator of wound response (herbivore attack), pathogen defense, pollen development, and some stress responses. Triggers protease inhibitor gene expression.
Q23.
Epigenetic regulation of flowering time in Arabidopsis involves:
A Direct DNA methylation of the FT gene promoter region alone, with little histone involvement noted in typical laboratory settings
B FLC (Flowering Locus C) - a repressor of flowering - silenced by vernalization through polycomb-mediated H3K27me3 marking
C Gibberellin signaling acting mainly alone through the DELLA degradation pathway each time under usual circumstances
D Mainly transcriptional control with little chromatin-level modification involved overall according to most researchers
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Answer: B. FLC (Flowering Locus C) - a repressor of flowering - silenced by vernalization through polycomb-mediated H3K27me3 marking
Why: FLC represses flowering. Vernalization causes polycomb repressive complex (PRC2) to add H3K27me3 marks to FLC chromatin, silencing it. This allows FT expression and flowering.
Q24.
Calmodulin in plant signal transduction:
A Functions as a receptor tyrosine kinase embedded directly in the plasma membrane structure under most conditions encountered
B Is a calcium sensor that, when Ca2+ bound, activates multiple target enzymes (kinases, phosphatases, NOSs)
C Operates mainly within guard cells, largely absent from other plant tissues studied as frequently observed in practice
D Is itself a diffusible plant hormone synthesized within the shoot apex region in many documented cases
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Answer: B. Is a calcium sensor that, when Ca2+ bound, activates multiple target enzymes (kinases, phosphatases, NOSs)
Why: Calmodulin: ubiquitous Ca2+-binding protein. Ca2+ binding changes its conformation, enabling it to activate/inhibit target proteins, transducing Ca2+ signals to diverse cellular responses.
Q25.
Phytochrome-interacting factors (PIFs) are:
A Red light receptors themselves, which absorb photons directly through a bound chromophore group structure according to conventional understanding
B Transcription factors that interact with Pfr form of phytochrome and are degraded upon light activation, derepressing light-responsive genes
C Plastid-localized enzymes responsible for synthesizing the phytochrome chromophore precursor molecule in routine practice overall in most cases
D DNA repair proteins that are activated specifically in response to ultraviolet light exposure events under typical conditions according to standard textbooks
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Answer: B. Transcription factors that interact with Pfr form of phytochrome and are degraded upon light activation, derepressing light-responsive genes
Why: PIFs: bHLH transcription factors. In dark, PIFs accumulate and repress light responses. Light converts phytochrome to Pfr; Pfr binds PIFs and promotes their phosphorylation and proteasomal degradation.
A Primary root elongation by suppressing meristematic cell division at the root tip
B Shoot branching (axillary bud outgrowth) and promote mycorrhizal symbiosis
C Seed germination in the surrounding rhizosphere soil community
D Stomatal opening by maintaining elevated guard cell turgor pressure
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Answer: B. Shoot branching (axillary bud outgrowth) and promote mycorrhizal symbiosis
Why: Strigolactones: inhibit shoot branching (synergistic with auxin, antagonistic with cytokinin); promote mycorrhizal fungus hyphal branching for symbiosis; germination stimulant for parasitic plants.
Q27.
The 'triple response' of pea seedlings (reduced stem elongation, increased stem thickening, and horizontal growth) is a classic bioassay for which plant hormone?
A Gibberellin
B Ethylene
C Auxin
D Cytokinin
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Answer: B. Ethylene
Why: The triple response (inhibition of elongation, radial swelling, and horizontal growth of seedlings) is a well-known bioassay used to detect ethylene activity.
Q28.
Abscisic acid is often called a 'stress hormone' in plants mainly because it:
A Promotes stomatal closure and dormancy in response to water stress
B Stimulates seed germination under high humidity conditions
C Promotes flowering specifically in response to cold temperatures
D Promotes rapid cell elongation under conditions of high water availability
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Answer: A. Promotes stomatal closure and dormancy in response to water stress
Why: Abscisic acid accumulates under water stress and other unfavourable conditions, promoting stomatal closure to reduce water loss and inducing seed and bud dormancy.
Q29.
Auxin transport within plant tissues is largely polar (mainly basipetal in stems), a property explained by:
A Auxin's inability to cross the plasma membrane in either direction
B Auxin being synthesized only at the base of the stem
C Asymmetric distribution of auxin efflux carriers (PIN proteins) on the cell membrane
D Passive diffusion alone, without involvement of any membrane transport proteins
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Answer: C. Asymmetric distribution of auxin efflux carriers (PIN proteins) on the cell membrane
Why: Polar auxin transport depends on the asymmetric, unequal localization of PIN efflux carrier proteins on the plasma membrane, directing the movement of auxin predominantly toward the base of the shoot.
A Inhibiting cell division in the apical meristem entirely
B Stimulating cell elongation and division in the stem internodes
C Causing abscission of the existing leaves on the rosette
D Triggering immediate seed dormancy in the same plant
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Answer: B. Stimulating cell elongation and division in the stem internodes
Why: Gibberellins promote bolting by stimulating both cell elongation and cell division in stem internodes, causing the characteristic rapid increase in stem length seen in rosette plants before flowering.