I. INTRODUCTION & BASICS
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| FEATURE | DETAIL |
|---|---|
| All cells of a plant | Descendants of the zygote ⭐ |
| Development | Sum of two processes: Growth + Differentiation ⭐⭐ |
| ATP | Energy currency of the cell ⭐ |
| First step of plant growth | Seed germination ⭐ |
| If favourable conditions absent | Seeds go into suspended growth / rest (dormancy) ⭐ |
II. GROWTH — DEFINITION & CHARACTERISTICS
A DEFINITION
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| FEATURE | DETAIL |
|---|---|
| Growth | An irreversible permanent increase in size of an organ or its parts or even of an individual cell ⭐⭐⭐ |
| Accompanied by | Metabolic processes (both anabolic and catabolic), at the expense of energy ⭐⭐ |
| Example of growth | Expansion of a leaf ⭐ |
| NOT growth | Swelling of a piece of wood in water (reversible, non-living) ⭐ |
B PLANT GROWTH IS INDETERMINATE
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| FEATURE | DETAIL |
|---|---|
| Plant growth | Generally indeterminate — continues throughout life ⭐⭐⭐ |
| Reason | Presence of meristems at certain locations in the body ⭐⭐ |
| Meristematic cells | Have capacity to divide and self-perpetuate ⭐ |
| Open form of growth | New cells are always being added to the plant body by activity of meristem ⭐⭐ |
| Root + Shoot apical meristem | Responsible for primary growth (elongation along axis) ⭐ |
| Lateral meristems | Vascular cambium and cork cambium — appear later in dicots & gymnosperms → cause increase in girth = secondary growth ⭐⭐ |
⚡ EXAM TRAP
NEET 2023: 'Plant growth is generally determinate' — this is INCORRECT; plant growth is INDETERMINATE.
C GROWTH IS MEASURABLE
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| FEATURE | DETAIL |
|---|---|
| At cellular level | Growth is principally a consequence of increase in the amount of protoplasm ⭐⭐ |
| Parameters | Increase in fresh weight, dry weight, length, area, volume, and cell number ⭐⭐ |
| Maize root apical meristem | Can give rise to more than 17,500 new cells per hour ⭐ |
| Watermelon cells | May increase in size by up to 3,50,000 times ⭐ |
| Pollen tube growth | Measured in terms of its length ⭐⭐ |
| Dorsiventral leaf growth | Measured as increase in surface area ⭐ |
III. GROWTH — PHASES
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| PHASE | CHARACTERISTICS |
|---|---|
| 1. Meristematic phase | Cells rich in protoplasm; large conspicuous nuclei; cell walls are primary, thin, cellulosic with abundant plasmodesmatal connections; cells are actively dividing ⭐⭐⭐ |
| 2. Elongation phase | Increased vacuolation; cell enlargement; new cell wall deposition; cells proximal to (just next to, away from tip) meristematic zone ⭐⭐⭐ |
| 3. Maturation phase | Cells attain maximal size; wall thickening and protoplasmic modifications; further away from apex ⭐⭐ |
IV. GROWTH RATES (ARITHMETIC VS GEOMETRIC)
A DEFINITION
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| FEATURE | DETAIL |
|---|---|
| Growth rate | Increased growth per unit time ⭐ |
| Types | Arithmetic or Geometrical ⭐⭐ |
B ARITHMETIC GROWTH
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| FEATURE | DETAIL |
|---|---|
| Cell division pattern | Only one daughter cell continues to divide; other differentiates and matures ⭐⭐ |
| Example | Root elongation at a constant rate ⭐⭐ |
| Curve | Linear curve (straight line when length plotted vs time) ⭐ |
| Formula | Lₜ = L₀ + rt ⭐⭐ |
| Lₜ | Length at time 't' ⭐ |
| L₀ | Length at time 'zero' ⭐ |
| r | Growth rate / elongation per unit time ⭐ |
⚡ EXAM TRAP
RE-NEET 2026 (reinforced): Arithmetic growth follows Lₜ = L₀ + rt.
C GEOMETRICAL GROWTH
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| FEATURE | DETAIL |
|---|---|
| Cell division pattern | Both daughter cells continue to divide ⭐⭐ |
| Three phases | Lag phase → Log/Exponential phase → Stationary phase ⭐⭐⭐ |
| Lag phase | Initial slow growth ⭐ |
| Log (Exponential) phase | Growth increases rapidly; maximum growth occurs ⭐⭐⭐ |
| Stationary phase | Growth slows down due to limited nutrient supply ⭐ |
| Curve | Sigmoid or S-curve when parameter of growth plotted against time ⭐⭐⭐ |
| Formula | W₁ = W₀ × eʳᵗ ⭐⭐ |
| 'r' | Relative growth rate = Efficiency index ⭐⭐ |
| Final size W₁ depends on | Initial size W₀ ⭐ |
⚡ EXAM TRAP
NEET 2015: Sigmoid / S-curve obtained when growth parameter plotted against time.
⚡ EXAM TRAP
NEET 2020: Maximum growth occurs during log/exponential phase.
D ABSOLUTE vs RELATIVE GROWTH RATE
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| TYPE | DEFINITION |
|---|---|
| Absolute growth rate | Measurement and comparison of total growth per unit time ⭐⭐ |
| Relative growth rate | Growth of the given system per unit time expressed on a common basis (e.g., per unit initial parameter) ⭐⭐ |
V. CONDITIONS FOR GROWTH
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| ESSENTIAL ELEMENT | ROLE |
|---|---|
| Water | Provides medium for enzymatic activities; turgidity helps in extension growth; plant growth linked to water status ⭐⭐ |
| Oxygen | Helps in releasing metabolic energy essential for growth ⭐ |
| Nutrients | (Macro and micro) Required for synthesis of protoplasm and act as source of energy ⭐ |
| Temperature | Every plant has optimum range; deviation can be detrimental ⭐ |
| Light and Gravity | Environmental signals that affect certain phases/stages of growth ⭐ |
VI. DIFFERENTIATION, DEDIFFERENTIATION & REDIFFERENTIATION
A OVERVIEW
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| TERM | DEFINITION | EXAMPLES | DIVISION ABILITY |
|---|---|---|---|
| Differentiation | Cells from meristems mature to perform specific functions ⭐⭐ | Parenchyma, Collenchyma, Sclerenchyma, Primary xylem, Primary phloem ⭐ | Lost ⭐ |
| Dedifferentiation | Living differentiated cells regain capacity of division ⭐⭐⭐ | Interfascicular cambium, Cork cambium (from parenchyma cells) ⭐⭐ | Regained ⭐⭐ |
| Redifferentiation | Dedifferentiated cells lose capacity to divide again & mature ⭐⭐ | Secondary xylem, Secondary phloem, Cork, Secondary cortex ⭐⭐ | Permanently lost ⭐ |
⚡ EXAM TRAP
NEET 2022, 2025 (reinforced): Differentiation → Dedifferentiation → Redifferentiation sequence. Dedifferentiation is pre-requisite for redifferentiation.
⚡ EXAM TRAP
NEET 2023, 2024: Dedifferentiation examples = interfascicular cambium, cork cambium; callus from leaf mesophyll in tissue culture.
B ADDITIONAL FACTS
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| FEATURE | DETAIL |
|---|---|
| Tracheary element formation | Cells lose protoplasm; develop strong, elastic, lignocellulosic secondary cell walls → carry water under extreme tension ⭐ |
| Differentiation in plants | Open — cells/tissues from same meristem have different structures at maturity ⭐ |
| Final structure determined by | Location of cell within the organ ⭐ |
⚡ EXAM TRAP
NEET 2022: Undifferentiated cells = shoot & root apical meristem.
VII. DEVELOPMENT & PLASTICITY
A DEVELOPMENT
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| FEATURE | DETAIL |
|---|---|
| Development | Includes all changes an organism goes through during its life cycle — from germination of seed to senescence ⭐⭐ |
| Development = | Growth + Differentiation ⭐⭐ |
| Controlled by | Intrinsic factors + Extrinsic factors ⭐⭐ |
| Intrinsic factors | Intracellular (genetic) + Intercellular (PGRs — plant growth regulators) ⭐⭐ |
| Extrinsic factors | Light, Temperature, Water, Oxygen, Nutrition ⭐ |
B PLASTICITY
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| FEATURE | DETAIL |
|---|---|
| Plasticity | Ability of plants to follow different pathways in response to environment or phases of life to form different kinds of structures ⭐⭐⭐ |
| Example | Heterophylly — leaves of juvenile plant different from mature plant ⭐⭐ |
| Heterophylly examples | Cotton, Coriander, Larkspur (developmental plasticity) ⭐⭐ |
| Environmental heterophylly | Buttercup — leaves produced in air differ in shape from those produced in water ⭐⭐ |
⚡ EXAM TRAP
NEET 2021, 2022, 2026 (reinforced): Plasticity = heterophyllous development in response to environment or life phases; examples = cotton, coriander, larkspur, buttercup.
⚡ EXAM TRAP
NEET 2022: Maize does NOT show plasticity (TRAP!).
VIII. PLANT GROWTH REGULATORS — OVERVIEW & DISCOVERY
A CHARACTERISTICS
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| FEATURE | DETAIL |
|---|---|
| PGRs | Small, simple molecules of diverse chemical composition ⭐⭐ |
| Also called | Plant growth substances, Plant hormones, Phytohormones ⭐ |
| PGR | CHEMICAL NATURE |
|---|---|
| Auxins | Indole compounds (IAA) ⭐⭐ |
| Cytokinins | Adenine derivatives (Kinetin) ⭐⭐ |
| Gibberellins | Terpenes (GA₃) ⭐⭐ |
| Abscisic acid | Derivative of Carotenoids ⭐⭐ |
| Ethylene | Gas (C₂H₄) ⭐⭐ |
B CLASSIFICATION BY FUNCTION
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| CATEGORY | PGRS | KEY ACTIVITIES |
|---|---|---|
| Growth Promoters | Auxins, Gibberellins, Cytokinins ⭐⭐ | Cell division, enlargement, flowering, fruiting, seed ⭐ |
| Growth Inhibitor | ABA ⭐⭐ | Dormancy, abscission, stress responses ⭐ |
| Both (largely inhibitor) | Ethylene ⭐⭐⭐ | Promoter AND inhibitor, but largely inhibitor of growth ⭐⭐ |
⚡ EXAM TRAP
NEET 2025: Plant growth regulators can be involved in promotion as well as inhibition of growth.
C DISCOVERY OF PGRs
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| PGR | DISCOVERER | KEY EXPERIMENT |
|---|---|---|
| Auxin | F.W. Went ⭐⭐⭐ | Isolated from tips of coleoptiles of oat seedlings ⭐ |
| Gibberellin | E. Kurosawa (1926) ⭐⭐ | 'Bakanae' (foolish seedling) disease of rice; Gibberella fujikuroi ⭐⭐⭐ |
| Cytokinin | Skoog & Miller (1955) ⭐⭐ | Kinetin from autoclaved herring sperm DNA ⭐⭐ |
| ABA | Three researchers (mid-1960s) ⭐ | Inhibitor-B = Abscission II = Dormin → named ABA ⭐⭐ |
| Ethylene | H.H. Cousins (1910) ⭐⭐ | Volatile substance from ripened oranges hastened ripening of bananas ⭐⭐ |
⚡ EXAM TRAP
NEET 2016: Auxin isolated by F.W. Went from tips of oat coleoptiles.
⚡ EXAM TRAP
NEET 2014: Bakanae disease — Gibberella fujikuroi — gibberellin discovery.
IX. AUXINS
A BASICS
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| FEATURE | DETAIL |
|---|---|
| Name origin | Greek 'auxein' = to grow ⭐ |
| First isolated from | Human urine ⭐⭐ |
| Produced by | Growing apices of stems and roots → migrate to regions of action ⭐⭐ |
| Natural auxins | IAA (Indole-3-acetic acid) and IBA (Indole butyric acid) ⭐⭐⭐ |
| Synthetic auxins | 2,4-D (2,4-dichlorophenoxyacetic acid) and NAA (Naphthalene acetic acid) ⭐⭐⭐ |
⚡ EXAM TRAP
NEET 2013: IAA and IBA = natural auxins. 2,4-D and NAA = synthetic auxins.
B BIOASSAY & C. PHOTOTROPISM
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| FEATURE | DETAIL |
|---|---|
| Bioassay for auxins | Avena coleoptile curvature test ⭐⭐ |
| Phototropism mechanism | Auxin accumulates on the shaded side of the stem → stimulates greater cell elongation → plant bends towards light ⭐⭐ |
⚡ EXAM TRAP
NEET 2014, 2015, 2016: Avena coleoptile curvature test = bioassay for auxins.
D FUNCTIONS OF AUXINS
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| FUNCTION | DETAIL |
|---|---|
| Initiate rooting | In stem cuttings — widely used for plant propagation ⭐⭐ |
| Promote flowering | e.g., in Pineapples ⭐⭐ |
| Prevent fruit & leaf drop | At early stages ⭐⭐ |
| Promote abscission | Of older mature leaves and fruits ⭐⭐ |
| Apical dominance | Growing apical bud inhibits growth of lateral (axillary) buds ⭐⭐⭐ |
| Decapitation | Removal of shoot tips → growth of lateral buds → used in tea plantations and hedge-making ⭐⭐ |
| Parthenocarpy | Induces parthenocarpy in Tomatoes ⭐⭐ |
| Herbicide | 2,4-D kills dicot weeds; does NOT affect mature monocots → used for weed-free lawns ⭐⭐⭐ |
| Xylem differentiation | Controls xylem differentiation ⭐ |
| Tissue culture | Auxin + Cytokinin needed for both roots and shoots ⭐⭐ |
⚡ EXAM TRAP
NEET 2021, 2024, RE-NEET 2026 (reinforced): 2,4-D is used as herbicide; kills dicot weeds without affecting mature monocots.
⚡ EXAM TRAP
NEET 2022, 2025: Parthenocarpy can be induced by auxins in tomatoes. Apical dominance inhibits growth of lateral buds (does not promote!).
X. GIBBERELLINS
A BASICS
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| FEATURE | DETAIL |
|---|---|
| Number | More than 100 gibberellins reported ⭐ |
| First discovered | GA₃ (Gibberellic acid) ⭐⭐ |
| Nature | All GAs are acidic ⭐⭐ |
| Classification | Terpenes ⭐ |
| Type | Growth promoter ⭐ |
⚡ EXAM TRAP
NEET 2024: All GAs are acidic.
B FUNCTIONS OF GIBBERELLINS
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| FUNCTION | DETAIL |
|---|---|
| Grape stalks | Increases length of grape stalks ⭐⭐ |
| Apple | Causes elongation and improves shape ⭐ |
| Delay senescence | Fruits can be left on tree longer → extend market period ⭐⭐ |
| Malting process | GA₃ used to speed up malting in brewing industry ⭐⭐ |
| Sugarcane yield | Spraying increases stem length → yield increases by as much as 20 tonnes per acre ⭐⭐⭐ |
| Juvenile conifers | Spraying with GAs hastens maturity period → leads to early seed production ⭐⭐⭐ |
| Bolting | Promotes bolting (internode elongation just prior to flowering) in beet, cabbages, and rosette habit plants ⭐⭐⭐ |
| Seed germination | Mobilises stored food in the seed during germination ⭐⭐ |
⚡ EXAM TRAP
NEET 2020, 2024, RE-NEET 2026 (reinforced): Spraying sugarcane with GAs increases stem length → yield increase up to 20 tonnes/acre. Gibberellin promotes internode elongation prior to flowering in cabbage — bolting!
⚡ EXAM TRAP
NEET 2023, 2026 (reinforced): Spraying juvenile conifers with GAs → early seed production. GA₃ is used in brewing industry for malting.
XI. CYTOKININS
A BASICS
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| FEATURE | DETAIL |
|---|---|
| Specific effect on | Cytokinesis (cell division) ⭐⭐ |
| Chemical nature | Adenine derivative (modified form of adenine, a purine) ⭐⭐⭐ |
| Kinetin | Discovered from autoclaved herring sperm DNA; does NOT occur naturally in plants ⭐⭐⭐ |
| Zeatin | Isolated from corn-kernels and coconut milk → natural cytokinin ⭐⭐⭐ |
| Synthesised in | Regions of rapid cell division — root apices, developing shoot buds, young fruits ⭐⭐ |
| Discovery | Skoog and Miller — termed 'Kinetin' ⭐⭐ |
⚡ EXAM TRAP
NEET 2022: Cytokinin = adenine derivative.
B FUNCTIONS OF CYTOKININS
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| FUNCTION | DETAIL |
|---|---|
| Promote new leaves | ⭐ |
| Promote chloroplasts | In leaves ⭐ |
| Lateral shoot growth | ⭐ |
| Adventitious shoot formation | ⭐ |
| Overcome apical dominance | ⭐⭐⭐ |
| Nutrient mobilisation | Helps in delay of leaf senescence ⭐⭐⭐ |
⚡ EXAM TRAP
NEET 2024, 2025, 2026 (reinforced): Cytokinin promotes nutrient mobilisation which helps delay leaf senescence. Kinetin helps in nutrient mobilisation. Overcomes apical dominance!
XII. ETHYLENE
A BASICS
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| FEATURE | DETAIL |
|---|---|
| Nature | Simple gaseous PGR (C₂H₄) ⭐⭐ |
| Synthesised in large amounts by | Tissues undergoing senescence and ripening fruits ⭐⭐ |
| Classification | Both promoter and inhibitor; largely inhibitor of growth activities ⭐⭐ |
| Most widely used PGR in | Agriculture ⭐⭐ |
| Most widely used compound | Ethephon — absorbed and transported in plant, releases ethylene slowly ⭐⭐ |
B FUNCTIONS OF ETHYLENE
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| FUNCTION | DETAIL |
|---|---|
| Horizontal growth | Of dicot seedlings ⭐ |
| Swelling + Apical hook | Swelling of axis; apical hook formation in dicot seedlings ⭐ |
| Senescence & abscission | Promotes senescence and abscission of plant organs, esp. leaves and flowers ⭐⭐ |
| Fruit ripening | Highly effective; enhances respiration rate during ripening = Respiratory climacteric ⭐⭐⭐ |
| Break dormancy | Breaks seed and bud dormancy; initiates germination in peanut seeds, sprouting of potato tubers ⭐ |
| Deep water rice | Promotes rapid internode/petiole elongation → helps leaves/shoot remain above water ⭐⭐⭐ |
| Root growth | Promotes root growth and root hair formation → increases absorption surface ⭐⭐ |
| Flowering | Initiates flowering in pineapples; induces flowering in mango ⭐⭐⭐ |
| Female flowers | Promotes female flowers in cucumbers → increases yield ⭐⭐⭐ |
| Ethephon uses | Hastens fruit ripening in tomatoes and apples; accelerates abscission (thinning of cotton, cherry, walnut) ⭐⭐ |
⚡ EXAM TRAP
NEET 2022, 2023: Ethylene → rapid internode/petiole elongation in deep water rice.
⚡ EXAM TRAP
NEET 2022, 2024: Ethylene promotes female flowers in cucumber → increases yield.
XIII. ABSCISIC ACID (ABA)
A BASICS
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| FEATURE | DETAIL |
|---|---|
| Also called | Stress hormone ⭐⭐⭐ |
| Chemical nature | Derivative of Carotenoids ⭐ |
| Classification | Growth inhibitor — general plant growth inhibitor and inhibitor of plant metabolism ⭐⭐ |
⚡ EXAM TRAP
NEET 2013, 2020, 2024: ABA = Stress hormone.
B FUNCTIONS OF ABA
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| FUNCTION | DETAIL |
|---|---|
| Inhibits seed germination | ⭐⭐ |
| Stimulates closure of stomata | ⭐⭐⭐ |
| Increases tolerance to stresses | Various kinds of biotic and abiotic stresses ⭐⭐⭐ |
| Seed development, maturation, dormancy | Plays important role ⭐⭐ |
| Desiccation tolerance | Helps seeds withstand desiccation by inducing dormancy ⭐⭐ |
| Antagonist to GAs | ABA acts as an antagonist of Gibberellins ⭐⭐⭐ |
⚡ EXAM TRAP
NEET 2012, 2024, 2025, 2026 (reinforced): ABA = antagonist of GAs. Abscisic acid is a plant growth inhibitor — not a promoter — and acts as stress hormone. Stimulates closure of stomata!
⚡ EXAM TRAP
NEET 2024 TRAP: 'Auxins are antagonists to GAs' — INCORRECT; ABA is the antagonist. 'ABA induces parthenocarpy' — INCORRECT; Auxins/GAs induce parthenocarpy.
XIV. PGR INTERACTIONS
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| FEATURE | DETAIL |
|---|---|
| PGR roles | Could be complementary or antagonistic ⭐⭐ |
| PGR roles | Could be individualistic or synergistic ⭐⭐ |
| Events with multiple PGR interaction | Dormancy of seeds/buds, Abscission, Senescence, Apical dominance ⭐⭐ |
| Extrinsic factors via PGRs | Vernalisation, Flowering, Dormancy, Seed germination, Plant movements ⭐ |
XV. RAPID REVISION — KEY COMPARISON TABLES
TABLE 1: Five Major PGRs — Chemical Nature & Discovery ⭐⭐⭐
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| PGR | CHEMICAL NATURE | DISCOVERED BY | SOURCE |
|---|---|---|---|
| Auxins | Indole compounds | F.W. Went | Tips of oat coleoptiles |
| Gibberellins | Terpenes | E. Kurosawa (1926) | Gibberella fujikuroi (Bakanae) |
| Cytokinins | Adenine derivatives | Skoog & Miller (1955) | Autoclaved herring sperm DNA |
| ABA | Carotenoid derivative | Three researchers (mid-1960s) | Inhibitor-B = Abscission II = Dormin |
| Ethylene | Gas (C₂H₄) | H.H. Cousins (1910) | Ripened oranges |
TABLE 2: Growth Promoters vs Inhibitors ⭐⭐⭐
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| CATEGORY | PGRS | KEY ACTIVITIES |
|---|---|---|
| Growth Promoters | Auxins, Gibberellins, Cytokinins | Cell division, enlargement, flowering, fruiting, seed |
| Growth Inhibitor | ABA | Dormancy, abscission, stress responses |
| Both (largely inhibitor) | Ethylene | Ripening, abscission, senescence + root growth, flowering |
TABLE 3: Natural vs Synthetic Auxins ⭐⭐⭐
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| TYPE | EXAMPLES |
|---|---|
| Natural | IAA (Indole-3-acetic acid), IBA (Indole butyric acid) |
| Synthetic | 2,4-D (2,4-dichlorophenoxyacetic acid), NAA (Naphthalene acetic acid) |
TABLE 4: Kinetin vs Zeatin ⭐⭐⭐
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| FEATURE | KINETIN | ZEATIN |
|---|---|---|
| Source | Autoclaved herring sperm DNA | Corn-kernels, Coconut milk |
| Natural / Synthetic | NOT natural (does not occur naturally in plants) | Natural cytokinin |
| Chemical nature | Modified form of adenine (purine) | — |
| Discovered by | Miller et al. (Skoog & co-workers) | — |
TABLE 5: Arithmetic vs Geometric Growth ⭐⭐⭐
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| FEATURE | ARITHMETIC GROWTH | GEOMETRIC GROWTH |
|---|---|---|
| Daughter cells dividing | Only one continues to divide | Both continue to divide |
| Example | Root elongation at constant rate | Cell culture; most organ growth |
| Curve | Linear | Sigmoid (S-curve) |
| Formula | Lₜ = L₀ + rt | W₁ = W₀ × eʳᵗ |
| Phases | — | Lag → Log → Stationary |
| Maximum growth | Constant rate | Log/Exponential phase |
TABLE 6: Differentiation → Dedifferentiation → Redifferentiation ⭐⭐⭐
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| STAGE | EXAMPLES | DIVISION ABILITY |
|---|---|---|
| Undifferentiated | Shoot & root apical meristem cells | Active division |
| Differentiated | Parenchyma, Collenchyma, Sclerenchyma, Primary xylem, Primary phloem | Lost |
| Dedifferentiated | Interfascicular cambium, Cork cambium | Regained |
| Redifferentiated | Secondary xylem, Secondary phloem, Cork, Secondary cortex | Permanently lost |
TABLE 7: Functions of All Five PGRs — Quick Reference ⭐⭐⭐
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| FUNCTION | AUXIN | GA | CK | ETH | ABA |
|---|---|---|---|---|---|
| Cell division | ✅ | — | ✅ | — | — |
| Cell elongation | ✅ | ✅ | — | — | — |
| Apical dominance | ✅ (causes) | — | Overcomes | — | — |
| Flowering | ✅ (Pineapple) | — | — | ✅ (Mango, Pineapple) | — |
| Bolting | — | ✅ | — | — | — |
| Fruit ripening | — | — | — | ✅ | — |
| Delays senescence | — | ✅ (fruits) | ✅ (leaves) | — | — |
| Promotes abscission | ✅ (older) | — | — | ✅ | — |
| Parthenocarpy | ✅ (Tomato) | — | — | — | — |
| Herbicide | ✅ (2,4-D) | — | — | — | — |
| Seed germination | — | ✅ | — | ✅ | Inhibits |
| Stomatal closure | — | — | — | — | ✅ |
| Stress tolerance | — | — | — | — | ✅ |
| Female flowers (Cucumber) | — | — | — | ✅ | — |
| Deep water rice elongation | — | — | — | ✅ | — |
| Root initiation (cuttings) | ✅ | — | — | — | — |
| Root growth & hair | — | — | — | ✅ | — |
| Sugarcane yield | — | ✅ | — | — | — |
| Antagonist to GAs | — | — | — | — | ✅ |
TABLE 8: Phases of Growth ⭐⭐⭐
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| PHASE | KEY FEATURES |
|---|---|
| Meristematic | Rich in protoplasm; large nuclei; primary, thin, cellulosic walls; abundant plasmodesmata; active division |
| Elongation | Increased vacuolation; cell enlargement; new cell wall deposition |
| Maturation | Maximal size; wall thickening; protoplasmic modifications |
TABLE 9: PGR-Specific Plant Examples ⭐⭐⭐
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| PLANT | PGR | EFFECT |
|---|---|---|
| Pineapple | Auxin + Ethylene | Promote flowering; synchronise fruit-set |
| Tomato | Auxin | Induces parthenocarpy |
| Sugarcane | Gibberellin | Increases stem length → yield up to 20 tonnes/acre |
| Grape | Gibberellin | Increases length of stalks |
| Beet, Cabbage | Gibberellin | Promotes bolting |
| Juvenile conifers | Gibberellin | Hastens maturity → early seed production |
| Rice | Gibberella fujikuroi | Bakanae disease |
| Deep water rice | Ethylene | Rapid internode/petiole elongation |
| Cucumber | Ethylene | Promotes female flowers → increases yield |
| Mango | Ethylene | Induces flowering |
| Cotton, Coriander, Larkspur | Plasticity | Heterophylly |
| Buttercup | Plasticity | Environmental heterophylly |
TABLE 10: Key Numbers & Facts — Quick Reference ⭐⭐⭐
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| PARAMETER | VALUE / FACT |
|---|---|
| Growth curve shape | Sigmoid / S-curve |
| Maximum growth phase | Log / Exponential phase |
| Growth type in plants | Indeterminate |
| Growth form | Open |
| Arithmetic growth formula | Lₜ = L₀ + rt |
| Geometric growth formula | W₁ = W₀ × eʳᵗ |
| 'r' in geometric formula | Relative growth rate = Efficiency index |
| Number of gibberellins | More than 100 |
| First gibberellin | GA₃ |
| Natural auxins | IAA, IBA |
| Synthetic auxins | 2,4-D, NAA |
| Kinetin source | Autoclaved herring sperm DNA |
| Zeatin source | Corn-kernels, Coconut milk |
| Ethylene = most widely used PGR in | Agriculture |
| Most widely used ethylene compound | Ethephon |
| ABA = also called | Stress hormone |
| ABA is antagonist to | Gibberellins (GAs) |
| Sugarcane yield increase with GA | 20 tonnes per acre |
| Auxin isolated from | Tips of oat coleoptiles (by F.W. Went) |
| Auxin first isolated from | Human urine |
| Maize root apical meristem | 17,500 new cells/hour |
| Watermelon cell size increase | Up to 3,50,000 times |
| Plasticity examples | Cotton, Coriander, Larkspur, Buttercup |
| NOT plasticity | Maize |
XVI. COMMON EXAM TRAPS — QUICK REFERENCE
NEET 2025, 2026 & RE-NEET 2026 REINFORCED TRAPS
RE-NEET 2026: Arithmetic growth follows Lₜ = L₀ + rt.
NEET 2025: Dedifferentiation is pre-requisite for redifferentiation.
NEET 2026: Heterophyllous development in response to environment is plasticity.
NEET 2025: Plant growth regulators can be involved in promotion as well as inhibition of growth.
RE-NEET 2026: 2,4-D is used as herbicide.
NEET 2025: Parthenocarpy can be induced by auxins. Apical dominance inhibits growth of lateral buds — not promote!
RE-NEET 2026: Gibberellin promotes internode elongation prior to flowering in cabbage — bolting.
NEET 2026: GA₃ is used in brewing industry for malting.
NEET 2025: Cytokinin promotes nutrient mobilisation which helps delay leaf senescence.
NEET 2026: Kinetin helps in nutrient mobilisation.
NEET 2025: Abscisic acid is a plant growth inhibitor — not a promoter — and acts as stress hormone.
NEET 2026: Abscisic acid stimulates closure of stomata.
CONSOLIDATED PYQ Q&A TABLE
↔ Swipe table sideways to view full columns
| TRAP / QUESTION | CORRECT ANSWER |
|---|---|
| Growth is? | Irreversible permanent increase in size ⭐ |
| Plant growth is determinate or indeterminate? | Indeterminate (TRAP: 'determinate' is WRONG) ⭐⭐ |
| Open form of growth? | New cells always being added to plant body ⭐ |
| Pollen tube growth measured by? | Length ⭐ |
| Dorsiventral leaf growth measured by? | Surface area ⭐ |
| Meristematic phase cells have? | Rich protoplasm; large nuclei; primary, thin, cellulosic walls; abundant plasmodesmata ⭐ |
| Maximum growth in which phase? | Log / Exponential phase ⭐ |
| Sigmoid/S-curve represents? | Growth parameter plotted against time in geometric growth ⭐ |
| 'r' in W₁=W₀eʳᵗ? | Relative growth rate = Efficiency index ⭐ |
| Differentiation = ? | Cells mature to perform specific functions ⭐ |
| Dedifferentiation examples? | Interfascicular cambium, Cork cambium ⭐ |
| Redifferentiation examples? | Secondary xylem, phloem, cork, secondary cortex ⭐ |
| Plasticity = ? | Different structures in response to environment or life phases ⭐ |
| Plasticity examples? | Cotton, Coriander, Larkspur, Buttercup ⭐ |
| Maize shows plasticity? | NO (TRAP!) ⭐⭐ |
| Development = ? | Growth + Differentiation ⭐ |
| Auxin chemical nature? | Indole compound ⭐ |
| Cytokinin chemical nature? | Adenine derivative ⭐ |
| Gibberellin chemical nature? | Terpene ⭐ |
| ABA chemical nature? | Carotenoid derivative ⭐ |
| Growth promoters? | Auxins, Gibberellins, Cytokinins ⭐ |
| Growth inhibitor? | ABA ⭐ |
| Ethylene is promoter or inhibitor? | Both, but largely inhibitor ⭐ |
| Auxin discovered by? | F.W. Went (from tips of oat coleoptiles) ⭐ |
| Bakanae disease pathogen? | Gibberella fujikuroi ⭐ |
| Kinetin source? | Autoclaved herring sperm DNA ⭐ |
| Kinetin is natural? | NO ⭐ |
| Zeatin is natural? | YES — from corn-kernels and coconut milk ⭐ |
| Auxin first isolated from? | Human urine ⭐ |
| Natural auxins? | IAA, IBA ⭐ |
| Synthetic auxins? | 2,4-D, NAA ⭐ |
| Auxin bioassay? | Avena coleoptile curvature test ⭐ |
| All GAs are? | Acidic ⭐ |
| ABA = ? | Stress hormone ⭐ |
| Auxin promotes flowering in? | Pineapple ⭐ |
| Apical dominance caused by? | Auxin (from apical bud) ⭐ |
| Cytokinin does what to apical dominance? | Overcomes it ⭐ |
| 2,4-D is? | Herbicide — kills dicot weeds; doesn't affect mature monocots ⭐ |
| Auxin induces parthenocarpy in? | Tomatoes ⭐ |
| GA on sugarcane? | Increases stem length → yield up to 20 tonnes/acre ⭐ |
| GA promotes? | Bolting in beet, cabbages, rosette plants ⭐ |
| GA on juvenile conifers? | Hastens maturity → early seed production ⭐ |
| Ethylene in deep water rice? | Rapid internode/petiole elongation ⭐ |
| Ethylene in cucumber? | Promotes female flowers → increases yield ⭐ |
| Ethylene in fruit ripening? | Highly effective; respiratory climacteric ⭐ |
| ABA inhibits? | Seed germination ⭐ |
| ABA stimulates? | Stomatal closure ⭐ |
| ABA is antagonist to? | GAs (NOT auxins!) ⭐⭐ |
| Auxins are antagonists to GAs? | NO (TRAP!) — ABA is the antagonist ⭐⭐ |
| ABA induces parthenocarpy? | NO (TRAP!) — Auxins induce parthenocarpy ⭐⭐ |
| Cytokinin delays leaf senescence via? | Nutrient mobilisation ⭐ |
| Tissue culture needs? | Auxin + Cytokinin for roots and shoots ⭐ |
| Most widely used PGR in agriculture? | Ethylene ⭐ |
| Most widely used ethylene compound? | Ethephon ⭐ |