Full Chapter Summary & Detailed Notes - Plant Growth and Development Class 11 NCERT
Overview & Key Concepts
- Chapter Goal: Explore how plants grow from zygote to maturity, focusing on growth, differentiation, development, and regulation by internal/external factors. Exam Focus: Phases of growth, PGRs (auxins, GAs, cytokinins, ethylene, ABA), plasticity. 2025 Updates: Emphasis on environmental influences and applications in agriculture. Fun Fact: Plants exhibit indeterminate growth due to meristems, unlike animals. Core Idea: Development = growth + differentiation, controlled by PGRs and extrinsic factors. Real-World: Crop yield enhancement via GA3 spraying.
- Wider Scope: Links to reproduction, ecology, biotechnology (tissue culture), and agriculture.
13.1 Growth
Growth is a fundamental characteristic of living organisms, defined as an irreversible permanent increase in size of an organ, its parts, or even a single cell. It involves metabolic processes (anabolic and catabolic) that require energy. For example, leaf expansion is growth, but wood swelling in water is not, as it's reversible.
- 13.1.1 Plant Growth Generally is Indeterminate: Unlike animals, plants have unlimited growth potential due to meristems (apical, lateral). Root and shoot apical meristems cause primary growth (elongation); vascular and cork cambium cause secondary growth (girth increase). Open form: New cells added continuously. If meristems cease, growth stops (e.g., in determinate plants like cereals).
- 13.1.2 Growth is Measurable: Measured indirectly via protoplasm increase parameters like fresh/dry weight, length, area, volume, cell number. Examples: Maize root meristem produces 17,500 cells/hour (cell number increase); watermelon cells enlarge 350,000 times (size increase); pollen tube by length; leaf by area.
- 13.1.3 Phases of Growth: Three phases - meristematic (division, protoplasm-rich, thin cellulosic walls), elongation (vacuolation, enlargement), maturation (wall thickening, protoplasmic modifications). Root tip example: Meristematic at apex, elongation proximal, maturation further away.
- 13.1.4 Growth Rates: Increased growth per unit time. Arithmetic: One daughter cell divides, other differentiates (linear curve, Lt = L0 + rt). Geometric: Both divide (exponential, sigmoid curve with lag, log, stationary phases; W1 = W0 e^rt). Absolute rate: Total growth/unit time; relative: Per unit initial parameter (e.g., leaf area comparison).
- 13.1.5 Conditions for Growth: Water (turgidity, enzyme medium), oxygen (energy release), nutrients (protoplasm synthesis), optimum temperature, light/gravity signals.
13.2 Differentiation, Dedifferentiation and Redifferentiation
Cells from meristems differentiate to perform specific functions, undergoing structural changes (e.g., tracheary elements lose protoplasm, gain lignocellulosic walls for water transport). Dedifferentiation: Differentiated cells regain division capacity (e.g., interfascicular cambium from parenchyma). Redifferentiation: New cells mature again (e.g., secondary tissues in woody plants). Open differentiation: Depends on cell position (e.g., root cap vs. epidermis). Tumors: Uncontrolled dedifferentiation; tissue culture: Controlled parenchyma division.
13.3 Development
Development encompasses all changes from seed germination to senescence, including growth and differentiation. Plants show plasticity: Response to environment/phases forming different structures (e.g., heterophylly - juvenile vs. mature leaves in cotton; air vs. water leaves in buttercup). Controlled by intrinsic (genetic, PGRs) and extrinsic (light, temperature) factors.
13.4 Plant Growth Regulators (PGRs)
PGRs are small molecules (indole compounds like IAA, adenine derivatives like kinetin, carotenoids like ABA, terpenes like GA3, gases like ethylene) acting as hormones.
- 13.4.1 Characteristics: Growth promoters (auxins, GAs, cytokinins: cell division/enlargement, flowering); inhibitors (ABA: dormancy, stress; ethylene: variable).
- 13.4.2 Discovery: Accidental - Auxins (Darwin's phototropism, Went's isolation); GAs ('bakanae' disease); Cytokinins (Skoog's callus culture); ABA (inhibitors from fruits); Ethylene (ripening gas).
- 13.4.3 Physiological Effects:
- Auxins (IAA, IBA, NAA, 2,4-D): Rooting in cuttings, flowering (pineapple), prevent early fruit drop, apical dominance, parthenocarpy (tomato), herbicides (2,4-D kills dicots).
- Gibberellins (GA3): Stem elongation (grapes, sugarcane yield +20 tonnes/acre), fruit shape (apple), delay senescence, malting, bolting (rosette plants like beet).
- Cytokinins (kinetin, zeatin): Cell division, new leaves/chloroplasts, lateral shoot growth, overcome apical dominance, delay senescence via nutrient mobilization.
- Ethylene: Senescence/abscission, fruit ripening (climacteric), break dormancy (peanut, potato), flood tolerance (deep water rice), female flowers (cucumber), via ethephon.
- Abscisic Acid (ABA): Stress hormone, inhibits growth/germination, stomatal closure, seed dormancy, antagonizes GAs.
PGRs act synergistically/antagonistically; interact with extrinsic factors (e.g., light/temperature for flowering).
Summary
Growth: Irreversible protoplasm increase via meristems (indeterminate). Phases: Meristematic, elongation, maturation. Rates: Arithmetic/geometric. Differentiation: Open, reversible (dediff/rediff). Development: Plastic, sum of growth+differentiation. PGRs: Five major groups control processes.
Why This Guide Stands Out
Complete coverage: All subtopics, diagrams explained, Q&A aligned to NCERT exercises. Exam-ready for 2025 with applications. Free & ad-free.
Key Themes & Tips
- Growth vs. Development: Growth quantitative; development qualitative.
- PGR Interactions: Synergistic (auxin+cytokinin for callus) or antagonistic (ABA vs. GA).
- Tip: Draw phases diagram; memorize PGR discoveries and applications.
Exam Case Studies
Questions on sigmoid curve, heterophylly examples, PGR roles in agriculture (e.g., GA3 in sugarcane).
Project & Group Ideas
- Observe seed germination phases; test PGR effects on bean cuttings.
- Discuss plasticity in local plants (e.g., water hyacinth).
60+ Questions & Answers - NCERT Based (Class 11)
Structured as Part A (1 mark, short answers), Part B (4 marks, ~6 lines/medium length), Part C (8 marks, detailed/long). 20 per part, aligned to NCERT exercises and concepts.
Part A: 1 Mark Questions (Short Answers)
1. Define growth.
1 Mark Answer: Irreversible permanent increase in size.
2. What causes indeterminate growth in plants?
1 Mark Answer: Meristems.
3. Primary growth meristems?
1 Mark Answer: Apical.
4. Secondary growth meristems?
1 Mark Answer: Vascular/cork cambium.
5. Growth measured by?
1 Mark Answer: Cell number/size.
6. Meristematic phase cells?
1 Mark Answer: Protoplasm-rich, thin walls.
7. Arithmetic growth equation?
1 Mark Answer: Lt = L0 + rt.
8. Geometric growth equation?
1 Mark Answer: W1 = W0 e^rt.
9. Sigmoid curve phases?
1 Mark Answer: Lag, log, stationary.
10. Essential for growth?
1 Mark Answer: Water, oxygen, nutrients.
11. Dedifferentiation example?
1 Mark Answer: Parenchyma to cambium.
12. Development includes?
1 Mark Answer: Germination to senescence.
13. Plasticity example?
1 Mark Answer: Heterophylly.
14. PGR group for promoters?
1 Mark Answer: Auxins, GAs, cytokinins.
15. Auxin discovery?
1 Mark Answer: Went's coleoptile.
16. GA from?
1 Mark Answer: Bakanae fungus.
17. Cytokinin natural source?
1 Mark Answer: Zeatin from corn.
18. Ethylene effect?
1 Mark Answer: Ripening.
19. ABA known as?
1 Mark Answer: Stress hormone.
20. Redifferentiation product?
1 Mark Answer: Secondary tissues.
Part B: 4 Marks Questions (Medium Length Answers ~6 Lines)
1. Differentiate arithmetic and geometric growth.
4 Marks Answer: Arithmetic: One cell divides, linear (Lt = L0 + rt), e.g., root constant rate. Geometric: Both divide, exponential/sigmoid (W1 = W0 e^rt), lag-log-stationary phases, e.g., embryo. Relative rate measures efficiency.
2. Explain phases of growth with root tip example.
4 Marks Answer: Meristematic: Division at apex, protoplasm-rich. Elongation: Proximal, vacuolation/enlargement. Maturation: Further, wall thickening. Root: Apical division, then elongation, then specialization.
3. What is plasticity? Give example.
4 Marks Answer: Environment-responsive structure formation. Heterophylly: Larkspur juvenile vs. adult leaves; buttercup air vs. water leaves. Shows developmental flexibility.
4. Describe dedifferentiation and redifferentiation.
4 Marks Answer: Dediff: Differentiated cells regain division (e.g., parenchyma to cambium). Rediff: New cells mature (e.g., secondary xylem/phloem). Enables wound healing, tissue culture.
5. List conditions for growth.
4 Marks Answer: Water (turgidity), oxygen (energy), nutrients (protoplasm), temperature (optimum), light/gravity (signals). Water links to extension; deviations detrimental.
6. Auxin physiological effects.
4 Marks Answer: Rooting cuttings, pineapple flowering, prevent early drop, apical dominance, parthenocarpy, herbicides (2,4-D dicots). Controls xylem, cell division.
7. GA applications.
4 Marks Answer: Grape stalk elongation, apple shape, sugarcane yield (+20t/acre), malting, bolting (beet), conifer maturity. Delays senescence.
8. Cytokinin functions.
4 Marks Answer: Cell division, chloroplasts, lateral shoots, overcome dominance, delay senescence (nutrient mobilization). Synthesized in root apices.
9. Ethylene roles.
4 Marks Answer: Ripening (climacteric), abscission, dormancy break (peanut), flood tolerance (rice), female flowers (cucumber). Ethephon source.
10. Why ABA stress hormone?
4 Marks Answer: Inhibits germination, closes stomata, increases stress tolerance (drought). Seed dormancy, antagonizes GAs.
11. Discovery of auxins.
4 Marks Answer: Darwin's phototropism; Went isolated from oat coleoptile tips. Transmissible influence causes bending.
12. Open differentiation.
4 Marks Answer: Meristem cells differentiate based on position. Example: Root cap (away), epidermis (periphery).
13. Absolute vs. relative growth.
4 Marks Answer: Absolute: Total/unit time. Relative: Per initial parameter. Smaller leaf higher relative despite same absolute increase.
14. Sigmoid curve significance.
4 Marks Answer: Natural growth in limited nutrients: Lag (slow), log (exponential), stationary (plateau). Typical for cells/organs.
15. PGR characteristics.
4 Marks Answer: Small molecules (indole, adenine, etc.); promoters/inhibitors. Synergistic/antagonistic actions.
16. Apical dominance mechanism.
4 Marks Answer: Auxin from tip inhibits laterals. Decapitation releases, promotes branches (tea/hedge use).
17. Heterophylly types.
4 Marks Answer: Developmental (cotton juvenile/mature); environmental (buttercup air/water). Plasticity example.
18. Climacteric in fruits.
4 Marks Answer: Ethylene-induced respiration rise for ripening. Example: Banana hastened by ripe oranges.
19. Role of water in growth.
4 Marks Answer: Cell enlargement, turgidity for extension, enzyme medium. Linked to plant water status.
20. PGR interactions.
4 Marks Answer: Complementary (auxin+cytokinin), antagonistic (ABA+GA). Control dormancy, abscission.
Part C: 8 Marks Questions (Detailed Long Answers)
1. Explain growth phases with diagram description.
8 Marks Answer: Growth divided into meristematic (constant division at apices, cells protoplasm-rich with large nuclei, primary thin cellulosic walls, plasmodesmata), elongation (proximal to meristem, increased vacuolation, cell enlargement, new wall deposition), maturation (further proximal, maximal size via wall thickening/protoplasmic modifications). Root tip: Apical meristematic, then elongation (detected by parallel lines, zones A-D elongate most), then maturation (tissues like xylem/phloem). This sequence ensures ordered development; most studied tissues represent maturation phase. Link to figures: Fig 13.3 shows elongation zones.
2. Describe arithmetic and geometric growth with equations and examples.
8 Marks Answer: Arithmetic: Post-mitosis, one cell divides (other matures), constant rate, linear curve (Fig 13.5). Equation: Lt = L0 + rt (L=length, r=rate, t=time). Example: Root elongation. Geometric: Both cells divide, initial lag (slow), exponential log phase, stationary (nutrient limit), sigmoid S-curve (Fig 13.6). Equation: W1 = W0 e^rt (W=size, e=base log). Example: Embryo (Fig 13.4c geometric then arithmetic). Absolute: Total/unit time; relative: Efficiency index, higher in smaller systems (Fig 13.7 leaf comparison).
3. Discuss differentiation, dedifferentiation, redifferentiation with examples.
8 Marks Answer: Differentiation: Meristem cells mature for functions, structural changes (walls/protoplasm). Example: Tracheary lose protoplasm, gain lignocellulosic walls for tension water transport. Open: Position-based (root: inner epidermis, outer cap). Dedifferentiation: Lost division regained under stress (e.g., parenchyma to interfascicular/cork cambium). Redifferentiation: Dediff cells produce maturing ones (e.g., secondary xylem/phloem in dicots). Tumor: Uncontrolled dediff; tissue culture: Controlled (callus). Enables plasticity; correlates anatomy to function (e.g., sieve tubes for phloem).
4. Explain development and plasticity in plants.
8 Marks Answer: Development: Zygote to senescence changes (Fig 13.8: division, plasmatic growth, expansion, differentiation, maturation, senescence). Sum of growth+differentiation; intrinsic (genetic/PGRs) + extrinsic (light/temp). Plasticity: Environment/life phase responses form structures (Fig 13.9 heterophylly). Developmental: Cotton/coriander juvenile (different shape) vs. mature leaves. Environmental: Larkspur terrestrial vs. aquatic (buttercup). Allows adaptation; closely tied to growth/differentiation events.
5. Detail conditions essential for plant growth.
8 Marks Answer: Water: Cell enlargement via turgidity, enzymatic medium; deficit halts extension. Oxygen: Aerobic respiration for energy. Nutrients: Macro/micro for protoplasm (N for proteins, P for ATP). Temperature: Optimum range; deviation lethal (enzymes denature). Light: Photomorphogenesis (e.g., phototropism). Gravity: Geotropism. All interact; e.g., water status affects PGR transport. Without, growth suspended (seed dormancy).
6. Physiological effects and applications of auxins.
8 Marks Answer: Produced at apices, migrate to action sites. Effects: Initiate rooting (cuttings propagation), pineapple flowering, early fruit/leaf drop prevention, older abscission promotion, apical dominance (Fig 13.11 decapitation branches), parthenocarpy (tomato seedless), xylem differentiation, cell division. Synthetic: NAA/2,4-D herbicides (dicot weeds, monocot safe). Urine-isolated IAA; IBA natural. Widely agricultural/horticultural.
7. Describe gibberellins: Discovery, effects, applications.
8 Marks Answer: >100 types (GA3 studied); from fungi/plants, acidic. Discovery: Kurosawa's 'bakanae' rice filtrate (Gibberella fujikuroi). Effects: Axis elongation, fruit elongation/shape (apple), senescence delay (market extension), carbohydrate mobilization (sugarcane). Applications: Grape stalks, sugarcane yield (20t/acre stem length), malting (brewing), conifer maturity, bolting (rosette beet/cabbage). Promotes flowering in long-day plants.
8. Explain cytokinins: Sources, functions.
8 Marks Answer: Adenine derivatives; kinetin (synthetic from herring DNA), zeatin (natural corn kernels/coconut milk). Synthesized in dividing regions (roots, buds, fruits). Functions: Cytokinesis, new leaves/chloroplasts, lateral/adventitious shoots, apical dominance overcome, senescence delay (nutrient mobilization from leaves to fruits/seeds). Interact with auxins for pattern formation.
9. Role of ethylene in plant processes.
8 Marks Answer: Gaseous, from senescing/ripening tissues. Effects: Seedling horizontal growth/apical hook, senescence/abscission (leaves/flowers), fruit ripening (respiratory climacteric), dormancy break (peanut seeds/potato tubers), deep water rice internode elongation (aerenchyma), root hair formation. Applications: Pineapple flowering sync, mango induction, ethephon for tomato/apple ripening, cotton thinning, cucumber females (yield+).
10. Why is ABA called stress hormone? Detailed role.
8 Marks Answer: Discovered as inhibitor-B/abscission II/dormin. General inhibitor of metabolism/growth. Roles: Seed germination inhibition, stomatal closure (water conservation), stress tolerance (drought/salt/cold via gene expression). Seed development/maturation/dormancy (desiccation withstand). Antagonizes GAs (dormancy vs. germination). Wide effects beyond abscission; essential for survival in adverse conditions.
11. Discovery of PGRs (all five).
8 Marks Answer: Accidental: Auxins (Darwin phototropism, Went 1928 coleoptile). GAs (Kurosawa 1926 bakanae filtrate). Cytokinins (Skoog 1955 tobacco callus with coconut/yeast, Miller kinetin). ABA (1960s inhibitors from fruits, identical chemically). Ethylene (Cousins 1910 orange gas ripens bananas). All led to understanding hormonal control.
12. Explain open growth and differentiation.
8 Marks Answer: Open growth: Meristems add cells lifelong (indeterminate). Differentiation open: Same meristem cells vary by position/maturity (e.g., root: cap/epidermis). Enables flexibility; contrasts determinate (limited). Ties to development plasticity.
13. PGR interactions with extrinsic factors.
8 Marks Answer: PGRs mediate light/temp effects: Photoperiodism (flowering via phytochrome-PGR), vernalization (cold via GA/ABA). Gravity/light tropisms (auxin redistribution). Nutrition/oxygen influence synthesis. Genomic control + extrinsic via PGRs regulate germination, movements, dormancy.
14. Significance of sigmoid growth curve.
8 Marks Answer: Represents natural limited-environment growth: Lag (adaptation), log (rapid exponential via mitosis), stationary (resource depletion). Characteristic of cells/tissues/organs (e.g., bacterial culture, plant organs). Relative rate (r) measures efficiency. Deviations in seasonal trees.
15. Agricultural applications of PGRs.
8 Marks Answer: Auxins: Propagation, weed control. GAs: Yield (sugarcane), malting. Cytokinins: Shelf-life (senescence delay). Ethylene: Ripening (ethephon tomatoes), thinning. ABA: Stress resistance breeding. Synergistic use enhances productivity.
16. Compare growth promoters and inhibitors.
8 Marks Answer: Promoters (auxins/GAs/cytokinins): Division/enlargement, flowering, fruiting. Inhibitors (ABA/ethylene): Dormancy, abscission, stress response. Ethylene dual. Interactions balance (e.g., auxin+GA elongation). Essential for regulated development.
17. Role of meristems in plant growth.
8 Marks Answer: Apical: Primary elongation (root/shoot). Lateral: Secondary girth (cambium). Intercalary: Grass elongation. Self-perpetuate, produce differentiating cells. Enable indeterminate open growth.
18. Explain heterophylly as plasticity.
8 Marks Answer: Different leaf forms: Developmental (larkspur juvenile simple vs. adult compound). Environmental (buttercup dissected air vs. submerged simple). Adaptive; controlled by PGRs/environment. Demonstrates flexible development pathways.
19. How PGRs control development phases.
8 Marks Answer: Cell division (cytokinins), elongation (auxins/GA), differentiation (auxins), dormancy (ABA), ripening (ethylene). Synergistic for pattern; antagonistic for balance. Extrinsic signals via PGRs (e.g., light auxin redistribution).
20. Significance of growth regulators in agriculture.
8 Marks Answer: Enhance yield (GA sugarcane), propagation (auxin cuttings), storage (cytokinin delay senescence), ripening control (ethylene), stress tolerance (ABA breeding). Economic: 20t/acre increase, reduced losses. Future: GM for PGR optimization.
Practice Tip: For 8 marks, include examples/equations/diagrams. Align to NCERT exercises.
Growth Phases - Detailed Explanations
Comprehensive breakdown of 13.1.3, with extensions to rates/conditions.
Meristematic Phase
Initial division phase at apices. Cells: Dense protoplasm, large nuclei, thin primary walls, plasmodesmata for communication. High metabolic rate. Example: Root/shoot tips add cells hourly (maize 17,500). Links to indeterminate growth.
Elongation Phase
Post-division: Vacuoles form, cells enlarge 5-10x, new walls deposit. Detected by marking (Fig 13.3 parallel lines; zones A-D max elongation). Water uptake key; auxins/GA promote. Prepares for maturation.
Maturation Phase
Final: Maximal size, wall thickening (lignin), protoplasm specialization (e.g., chloroplasts). Forms permanent tissues (xylem conducts). Most chapter-studied structures here. Rediff contributes in secondary growth.
Integration with Rates
Meristematic: Geometric (rapid cells). Elongation: Arithmetic (size). Overall sigmoid in organs. Conditions: Water for elongation turgor.
| Phase | Characteristics | Example |
|---|
| Meristematic | Division, thin walls | Apical meristem |
| Elongation | Enlargement, vacuoles | Root behind tip |
| Maturation | Thickening, function | Xylem vessels |
Tip: Sketch root tip for visuals. Relate to PGRs (cytokinins division).
Applications
Understanding phases aids breeding (e.g., GA for elongation in dwarfs). Disorders: If elongation fails, stunted growth.
