Plant Growth and Development — NEET Botany MCQs with answers

Plant Growth and Development is a Class 11 Botany chapter in the NEET (UG) syllabus. NEET720 has 684 reviewed practice questions on it, each with a quick answer and a step-by-step explanation. The 8 questions below are free and fixed, so you can bookmark this page; the full chapter, plus mistake tracking and spaced revision, is in the app.

Topics covered

Growth, Differentiation and Development · Auxins, Gibberellins and Cytokinins · Ethylene and Abscisic Acid · Growth rates · Plant hormones · Development · Phases of Growth · Growth Rate · Conditions for Growth · Differentiation, Dedifferentiation and Redifferentiation · Growth Regulators · Vernalisation · Seed Dormancy and Germination · Growth Basics · Auxins · Cytokinins · Photoperiodism · Vernalization · Seed Germination · Growth Regulators Overview · Seed Dormancy · Plant Growth · Plant Growth and Development · Growth · Hormones · Growth and differentiation · Gibberellins · Hormonal integration · Secondary growth · Ethylene · Auxin · Growth patterns · Abscisic acid · Cytokinin · Growth patterns and gibberellins · Differentiation and hormone balance · Auxin-cytokinin antagonism · Ethylene-auxin interaction · ABA-GA antagonism · Growth phases and differentiation zones

8 free Plant Growth and Development practice questions with answers

Choose an answer in your head before opening it. Each explanation says why the correct option is right and, where relevant, why the tempting wrong option is wrong.

1. Question 1 · easy · Auxins, Gibberellins and Cytokinins

   Plant growth regulators (PGRs) are best described as which of the following?

   • A.Small, simple molecules of diverse chemical composition that are effective at very low concentrations
   • B.Large complex proteins synthesised only in the root apical meristem
   • C.Inorganic mineral ions absorbed from the soil that directly build cell walls
   • D.Molecules effective only at high concentrations comparable to primary metabolites
   Show answer and explanation

   Answer: A. Small, simple molecules of diverse chemical composition that are effective at very low concentrations

   PGRs are small, simple organic molecules of diverse chemical nature (indole compounds, terpenes, adenine derivatives, carotenoid derivatives) that produce marked physiological responses at very low concentrations.

   NCERT defines plant growth regulators as small molecules of diverse chemical composition — some are indole compounds (auxins), some terpenes (gibberellins), some adenine derivatives (cytokinins), and others are simple gases (ethylene) or derived from carotenoids (ABA). A hallmark feature is that they exert profound physiological effects at very low concentrations, unlike primary metabolites needed in bulk. Option B wrongly equates PGRs with large proteins; option C confuses PGRs with minerals; option D contradicts the defining low-concentration efficacy.

   Common mistake: Assuming hormones must be large molecules like proteins to have a big physiological effect.

   Key point: PGRs are small, chemically diverse molecules active at very low concentrations.

2. Question 2 · medium · Auxins, Gibberellins and Cytokinins

   Statement I: Charles Darwin and his son Francis observed that coleoptiles of canary grass bend towards unilateral light, and that this bending is caused by a signal transmitted from the tip. Statement II: F.W. Went isolated the substance responsible for coleoptile curvature from Avena coleoptile tips and named it auxin. Which of the following is correct?

   • A.Statement I is true but Statement II is false
   • B.Both Statement I and Statement II are true
   • C.Statement I is false but Statement II is true
   • D.Both Statement I and Statement II are false
   Show answer and explanation

   Answer: B. Both Statement I and Statement II are true

   Darwin and Francis first observed phototropic bending in canary grass coleoptiles and inferred a transmissible signal from the tip; Went later isolated and named auxin from Avena coleoptile tips.

   Statement I is true: the Darwins' classic experiments with canary grass (Phalaris) coleoptiles showed that the tip perceives unilateral light and transmits an influence to the elongating region below, causing bending. Statement II is true: F.W. Went, working with oat (Avena sativa) coleoptiles, isolated the growth-promoting substance from the tips and named it auxin (from Greek 'auxein', to grow). Both statements accurately represent the well-documented discovery sequence.

   Common mistake: Mixing up who observed the phenomenon (Darwins) versus who isolated and named the hormone (Went).

   Key point: Darwin observed the phenomenon; Went isolated and named the hormone auxin from Avena coleoptiles.

3. Question 3 · easy · Auxins, Gibberellins and Cytokinins

   Tea garden workers regularly prune the apical bud of tea bushes to promote bushy lateral growth for higher leaf yield. Which physiological phenomenon and hormonal explanation underlies this practice?

   • A.Pruning has no hormonal basis; it merely provides more light to lower branches
   • B.Removing the apical bud increases gibberellin supply to roots, promoting lateral root branching
   • C.Pruning removes cytokinin produced at the tip, which was inhibiting lateral bud growth
   • D.Removing the apical bud eliminates the source of auxin that suppresses lateral buds, releasing apical dominance
   Show answer and explanation

   Answer: D. Removing the apical bud eliminates the source of auxin that suppresses lateral buds, releasing apical dominance

   The apical bud produces auxin that suppresses growth of lateral (axillary) buds — apical dominance. Decapitation removes this auxin source, releasing lateral buds to grow, which is exploited in tea pruning and hedge-making.

   Apical dominance is the phenomenon in which the growing apical bud inhibits the growth of lateral buds, mediated by auxin synthesised at the tip and transported basipetally. Removing the apical bud (decapitation/pruning) removes this auxin source, releasing lateral buds from inhibition, resulting in bushier growth. This principle is commercially exploited in tea plantations and hedge-pruning for ornamental shrubs. Option B and C misattribute the effect to gibberellin/cytokinin roles; option D ignores hormonal control entirely.

   Common mistake: Confusing which hormone (auxin vs cytokinin) suppresses versus promotes lateral bud growth.

   Key point: Apical bud auxin suppresses lateral buds; decapitation releases apical dominance — exploited in tea pruning.

4. Question 4 · medium · Auxins, Gibberellins and Cytokinins

   A horticulturist dips the cut end of a stem cutting in a rooting hormone powder before planting it in soil to raise a new plant vegetatively. Which auxin is most commonly used for this purpose, and what physiological effect does it produce?

   • A.GA3; it induces adventitious root initiation from the stem cutting
   • B.IBA/NAA; it induces adventitious root initiation from the stem cutting
   • C.Kinetin; it prevents the cutting from rotting by delaying senescence only
   • D.IBA/NAA; it prevents any root formation to force shoot growth first
   Show answer and explanation

   Answer: B. IBA/NAA; it induces adventitious root initiation from the stem cutting

   Auxins such as IBA and NAA are widely used as rooting hormones because they induce adventitious root formation in stem cuttings, a technique central to vegetative propagation in horticulture.

   One of the most economically important applications of auxin is inducing root initiation in stem cuttings, exploited for vegetative propagation of ornamental and horticultural plants. Commercial rooting hormone powders typically contain IBA (indole butyric acid) or NAA (naphthalene acetic acid), which stimulate adventitious root formation at the cut surface. GA3 (gibberellin) does not promote rooting in this manner, and cytokinins (like kinetin) are associated with cell division and delaying senescence, not root induction from cuttings.

   Common mistake: Assuming any plant hormone can serve as a rooting hormone rather than specifically auxins.

   Key point: IBA/NAA are used as rooting hormones to induce adventitious roots in stem cuttings.

5. Question 5 · medium · Auxins, Gibberellins and Cytokinins

   A farmer wants to remove broad-leaved dicot weeds from a wheat (monocot) field without harming the wheat crop. Which synthetic auxin, and at what concentration regime, achieves this selectively?

   • A.2,4-D at very low concentration, since low auxin concentrations are herbicidal to dicots
   • B.GA3 at high concentration, since gibberellins selectively damage broad-leaved plants
   • C.IAA at high concentration, since natural auxin is more potent as a herbicide than synthetic analogues
   • D.2,4-D at high concentration, since it selectively kills dicot weeds without affecting monocot crops
   Show answer and explanation

   Answer: D. 2,4-D at high concentration, since it selectively kills dicot weeds without affecting monocot crops

   2,4-D, a synthetic auxin, is used at high concentration as a selective herbicide that kills dicot weeds but does not harm monocot crops like wheat, because monocots are far less sensitive to auxin overdose.

   A key exam trap is the concentration-dependence of auxin effects: at LOW concentrations auxin promotes growth-related and abscission-preventing effects, while at HIGH concentrations synthetic auxins like 2,4-D become herbicidal, causing uncontrolled, disorganised growth that kills the plant. Monocots such as wheat are relatively insensitive to this herbicidal action, making 2,4-D a widely used selective herbicide against dicot weeds in cereal fields. GA3 and IAA are not used this way; IAA in particular is unstable and rapidly degraded, unlike synthetic 2,4-D.

   Common mistake: Believing herbicidal auxin action occurs at low concentration rather than high concentration.

   Key point: 2,4-D at high concentration is a selective dicot herbicide, harmless to monocot crops.

6. Question 6 · easy · Auxins, Gibberellins and Cytokinins

   At low concentrations, auxin has which of the following effects on leaves and fruits?

   • A.It prevents premature abscission (falling) of leaves and fruits
   • B.It accelerates abscission of leaves and fruits to promote earlier harvest
   • C.It has no measurable effect on leaf or fruit drop
   • D.It induces immediate leaf yellowing and chlorophyll breakdown
   Show answer and explanation

   Answer: A. It prevents premature abscission (falling) of leaves and fruits

   Low concentrations of auxin prevent premature fruit and leaf drop by inhibiting the formation of the abscission layer, a fact commercially exploited in orchard management.

   One of the classical physiological effects of auxin, at low concentration, is preventing abscission of leaves and fruits — auxin delays the formation of the abscission zone, keeping the organ attached longer. This is exploited commercially to reduce premature fruit drop in orchards. Options B, C, and D contradict this well-established effect, either reversing it or denying its existence.

   Common mistake: Confusing auxin's abscission-preventing role with ethylene's abscission-promoting role.

   Key point: Low-concentration auxin prevents leaf/fruit abscission, useful to reduce premature fruit drop.

7. Question 7 · hard · Auxins, Gibberellins and Cytokinins

   In which of the following NCERT-cited examples does auxin help induce flowering?

   • A.Wheat
   • B.Rice
   • C.Pineapple
   • D.Mustard
   Show answer and explanation

   Answer: C. Pineapple

   NCERT cites pineapple as a classic example where auxin application helps induce and synchronise flowering, useful for commercial fruit production.

   Among the many physiological roles of auxin, NCERT specifically mentions that auxin helps induce flowering in certain plants, citing pineapple as the classic example — commercial pineapple growers use auxin treatment to synchronise flowering and thus fruiting across a plantation. Wheat, mustard, and rice are not the textbook examples used for this particular auxin effect; rice is instead associated with the gibberellin/bakanae disease narrative.

   Common mistake: Mixing up the pineapple-auxin flowering example with the rice-gibberellin bakanae example.

   Key point: Auxin can induce/synchronise flowering, classic NCERT example: pineapple.

8. Question 8 · easy · Auxins, Gibberellins and Cytokinins

   The 'bakanae' or foolish seedling disease of rice, in which infected seedlings become abnormally tall and spindly, led to the discovery of gibberellins. Which fungus, studied by Kurosawa, causes this disease?

   • A.Puccinia graminis
   • B.Gibberella fujikuroi
   • C.Ustilago maydis
   • D.Rhizopus stolonifer
   Show answer and explanation

   Answer: B. Gibberella fujikuroi

   Kurosawa found that rice seedlings infected with the fungus Gibberella fujikuroi showed excessive, abnormal elongation (bakanae disease), which led to the isolation of gibberellins.

   The bakanae ('foolish seedling') disease of rice causes infected plants to grow abnormally tall due to a substance secreted by the fungus Gibberella fujikuroi. Kurosawa's studies on this disease-causing fungus led directly to the discovery and isolation of gibberellins, hormones later found to be produced naturally by plants themselves. The other fungi listed (rust, smut, bread mould) are unrelated to this discovery history.

   Common mistake: Confusing Gibberella fujikuroi with other well-known plant pathogenic fungi.

   Key point: Gibberellins were discovered via bakanae disease of rice caused by the fungus Gibberella fujikuroi.

Questions about Plant Growth and Development for NEET

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Questions are original NEET720 compositions reviewed for correctness, syllabus fit and option quality. Counts update as the bank grows (684 active practice questions in this chapter today).