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Plant Growth and Development – Class 11 Biology Chapter 13 Notes & NCERT PDF

Class 11BiologyChapter 13NCERT book: Biology - Class 11

Notes and a simple summary of Chapter 13 of the NCERT Class 11 Biology book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 13: Plant Growth and Development

Introduction

A plant starts as a zygote, grows into a seed, germinates, and develops roots, leaves, branches, flowers and fruits. All these changes happen in an orderly sequence. This chapter studies growth, differentiation and development, and the chemical plant growth regulators (PGRs) that control them.

Key Concepts

13.1 Growth

Growth is an irreversible, permanent increase in size of an organ, its parts or even an individual cell, accompanied by metabolic processes at the expense of energy. Expansion of a leaf is growth; the swelling of wood in water is not (it is reversible and not metabolic).

13.1.1 Plant growth is generally indeterminate. Plants keep the capacity for unlimited growth because of meristems, whose cells divide and self-perpetuate. New cells are always being added — the open form of growth.

  • Root and shoot apical meristems → primary growth (elongation along the axis).
  • Lateral meristems (vascular cambium and cork cambium) in dicots and gymnosperms → secondary growth (increase in girth).

    • 13.1.2 Growth is measurable. Growth at the cellular level is mainly an increase in protoplasm, which is hard to measure, so we use fresh weight, dry weight, length, area, volume and cell number.

  • A single maize root apical meristem can produce more than 17,500 new cells per hour (growth as cell number).
  • Cells of a watermelon may increase in size by up to 3,50,000 times (growth as cell size).
  • Pollen tube: length; dorsiventral leaf: surface area.

    • 13.1.3 Phases of growth (seen at root tips, Figure 13.3, parallel-line technique):

  • Meristematic — constantly dividing cells; rich protoplasm, large nuclei, thin primary cellulosic walls, abundant plasmodesmata.
  • Elongation — increased vacuolation, cell enlargement, new wall deposition.
  • Maturation — cells attain maximal size in wall thickening and protoplasmic modification.

    • 13.1.4 Growth rates. Increased growth per unit time is the growth rate.

  • Arithmetic growth: after mitosis only one daughter cell keeps dividing. Example: a root elongating at a constant rate; length vs time gives a straight line. Lt = L₀ + rt.
  • Geometric growth: both daughter cells keep dividing. Initial lag phase, then log (exponential) phase, then a stationary phase when nutrients limit — a sigmoid (S-) curve, typical of cells, tissues and organs growing in nature. W₁ = W₀eʳᵗ, where r is the relative growth rate (the efficiency index) and e is the base of natural logarithms.
  • Absolute growth rate: total growth per unit time. Relative growth rate: growth per unit time per unit initial size. Two leaves may both gain 5 cm² in the same time; the smaller one shows the higher relative growth rate.

    • 13.1.5 Conditions for growth: water (cell enlargement needs turgidity; medium for enzymes), oxygen (metabolic energy), nutrients (macro- and micro-elements for protoplasm and energy), an optimum temperature range, and environmental signals such as light and gravity.

    13.2 Differentiation, Dedifferentiation and Redifferentiation

  • Differentiation: cells from meristems and cambium mature to perform specific functions, with changes in walls and protoplasm (e.g., tracheary elements lose protoplasm and develop strong lignocellulosic secondary walls).
  • Dedifferentiation: living differentiated cells that had lost the ability to divide regain it — e.g., interfascicular cambium and cork cambium formed from fully differentiated parenchyma cells.
  • Redifferentiation: the products of dedifferentiated tissue again lose the ability to divide and mature for specific functions.
  • Differentiation in plants is open: the final structure also depends on a cell's location (cells away from the root apical meristem become root-cap cells; those pushed to the periphery become epidermis).

    • 13.3 Development

    Development includes all changes an organism goes through from germination of the seed to senescence. Plants follow different pathways in response to environment or life phase — plasticity:

  • Heterophylly due to life phase: juvenile and mature leaves differ in cotton, coriander and larkspur.
  • Heterophylly due to environment: leaves in air vs in water in buttercup.

    • Development = growth + differentiation, controlled by intrinsic factors (genetic, and intercellular chemicals such as PGRs) and extrinsic factors (light, temperature, water, oxygen, nutrition).

    13.4 Plant Growth Regulators

    13.4.1 Characteristics. Small, simple molecules of diverse chemistry: indole compounds (IAA); adenine derivatives (kinetin, N⁶-furfurylamino purine); carotenoid derivatives (ABA); terpenes (GA₃); gases (ethylene, C₂H₄). Also called growth substances, plant hormones or phytohormones.

  • Promoters: auxins, gibberellins, cytokinins (cell division, enlargement, tropic growth, flowering, fruiting, seed formation).
  • Inhibitors: abscisic acid (responses to wounds and stresses, dormancy, abscission).
  • Ethylene could fit either group but is largely an inhibitor.

    • 13.4.2 Discovery (each was accidental).

  • Auxin: Charles and Francis Darwin saw canary grass coleoptiles bend towards unilateral light (phototropism); the tip was the source of the influence. F.W. Went isolated auxin from oat coleoptile tips.
  • Gibberellin: 'bakanae' (foolish seedling) disease of rice caused by the fungus Gibberella fujikuroi; E. Kurosawa (1926) reproduced symptoms with sterile fungal filtrates; the substance was gibberellic acid.
  • Cytokinin: F. Skoog found tobacco internode callus proliferated only if auxin was supplemented with vascular extract, yeast extract, coconut milk or DNA; Miller et al. (1955) crystallised the active substance — kinetin.
  • ABA: mid-1960s — inhibitor-B, abscission II and dormin, later shown identical and named abscisic acid.
  • Ethylene: H.H. Cousins (1910) — a volatile substance from ripened oranges hastened ripening of stored bananas.

    • 13.4.3 Physiological effects.

  • Auxins (Greek auxein, to grow; first isolated from human urine). Natural: IAA, IBA; synthetic: NAA, 2,4-D. Initiate rooting in stem cuttings; promote flowering in pineapple; prevent early fruit and leaf drop but promote abscission of older leaves/fruits; cause apical dominance (removing the shoot tip — decapitation — lets lateral buds grow; used in tea plantations and hedges); induce parthenocarpy in tomatoes; 2,4-D kills dicot weeds without affecting monocots (weed-free lawns); control xylem differentiation and help cell division.
  • Gibberellins: over 100 reported (GA₁, GA₂, GA₃ ...); all acidic; GA₃ most studied. Increase grape stalk length; elongate and improve shape of apples; delay senescence; speed up malting in brewing; spraying sugarcane increases stem length and yield by as much as 20 tonnes per acre; hasten maturity in juvenile conifers (early seeds); promote bolting in beet, cabbage and rosette plants.
  • Cytokinins: discovered as kinetin from autoclaved herring sperm DNA (kinetin does not occur naturally in plants); natural zeatin from corn kernels and coconut milk. Synthesised where rapid division occurs (root apices, shoot buds, young fruits). Promote new leaves, chloroplasts, lateral shoot growth and adventitious shoots; overcome apical dominance; promote nutrient mobilisation that delays leaf senescence.
  • Ethylene: gaseous; made by senescing tissues and ripening fruits. Horizontal growth of seedlings, swelling of axis, apical hook in dicot seedlings; promotes senescence and abscission; highly effective in fruit ripening — raises respiration (the respiratory climactic); breaks seed and bud dormancy (peanut germination, potato sprouting); rapid internode/petiole elongation in deep water rice; promotes root growth and root hairs; initiates flowering and synchronises fruit-set in pineapples; induces flowering in mango. Ethephon releases ethylene slowly: hastens ripening in tomatoes and apples, accelerates abscission (thinning of cotton, cherry, walnut), promotes female flowers in cucumbers.
  • Abscisic acid: general growth inhibitor and inhibitor of metabolism; inhibits seed germination; stimulates closure of stomata; increases tolerance to stresses — the stress hormone; important in seed development, maturation and dormancy (helps seeds withstand desiccation). Usually acts as an antagonist to GAs.

    • PGRs may act complementarily or antagonistically, individually or synergistically; several interact in events such as dormancy, abscission, senescence and apical dominance. Extrinsic factors like temperature and light act via PGRs in vernalisation, flowering, dormancy, germination and plant movements.

    Diagrams to Know

  • Locations of root apical meristem, shoot apical meristem and vascular cambium (Figure 13.2).
  • Zones of meristematic activity, elongation and maturation at a root tip (parallel-line technique).
  • Arithmetic (straight-line) vs geometric (sigmoid) growth curves.
  • Coleoptile tip experiment showing auxin source; apical dominance before and after decapitation.
  • Heterophylly in larkspur and buttercup.

    • Key-Facts Sheet

  • Growth = irreversible permanent increase in size.
  • Maize root apex: >17,500 cells/hour; watermelon cells: up to 3,50,000× size.
  • Arithmetic: Lt = L₀ + rt; geometric: W₁ = W₀eʳᵗ.
  • Five PGR groups: auxins, gibberellins, cytokinins, ABA, ethylene.
  • ABA = stress hormone; ethephon = ethylene source; 2,4-D = dicot weedicide.
  • Sugarcane + GA: up to 20 tonnes per acre more yield.

    • Exam Focus

    Exercises ask you to define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate; explain why no single parameter shows growth throughout a plant's life; describe arithmetic vs geometric growth, sigmoid curve and absolute vs relative growth rate; list the five PGR groups with discovery, functions and applications of one; explain why ABA is the stress hormone and why "growth and differentiation in higher plants are open"; and choose the right PGR to induce rooting, quickly ripen fruit, delay leaf senescence, induce axillary bud growth, bolt a rosette plant or close stomata. They also ask what happens if GA₃ is applied to rice seedlings, a rotten fruit is mixed with unripe fruits, or cytokinin is left out of a culture medium.

    Key Terms

  • Growth (वृद्धि)
  • Meristem (विभज्योतक)
  • Differentiation (विभेदन)
  • Dedifferentiation (निर्विभेदन)
  • Redifferentiation (पुनर्विभेदन)
  • Development (परिवर्धन)
  • Plasticity (सुघट्यता)
  • Heterophylly (विषमपर्णता)
  • Plant growth regulator (पादप वृद्धि नियामक)
  • Apical dominance (शीर्ष प्रभाविता)
  • Parthenocarpy (अनिषेकफलन)
  • Bolting (बोल्टिंग / पुष्पवृंत दीर्घन)
  • Senescence (जीर्णता)
  • Abscission (विलगन)
  • Dormancy (प्रसुप्ति)

    • Common Mistakes

  • Calling any size increase growth — it must be irreversible and involve metabolism (swollen wood is not growth).
  • Confusing arithmetic growth (one daughter cell divides) with geometric growth (both divide).
  • Thinking kinetin is a natural plant hormone — it does not occur naturally in plants; zeatin does.
  • Mixing up roles: cytokinins overcome apical dominance, while auxins cause it.
  • Writing that 2,4-D kills monocot weeds — it kills dicot weeds in monocot lawns and crops.
  • Forgetting that ethylene is largely an inhibitor even though it promotes ripening and some growth responses.

    • 💡 Key Learning Points

    • ✓Define growth and explain why plant growth is open and indeterminate
    • ✓Describe the phases of growth and compare arithmetic and geometric growth
    • ✓Distinguish differentiation, dedifferentiation and redifferentiation with examples
    • ✓Explain development and plasticity using heterophylly
    • ✓Recall the discovery and physiological effects of the five groups of plant growth regulators

    👨‍🏫 Teaching Tips

    • →Mark a germinating root with equally spaced ink lines and observe which zone elongates after a day
    • →Plot class data of seedling height against days to show a sigmoid curve
    • →Show apical dominance by decapitating one of two identical potted plants
    • →Ripen raw bananas in a closed bag with a ripe fruit to show ethylene action
    • →Root stem cuttings with and without a rooting hormone powder (auxin)
    • →Make a PGR 'who am I?' card game from effects like bolting, stomatal closure and parthenocarpy

    📋 Assessment Questions

    1. Why is a root elongating at a constant rate an example of arithmetic growth?
    2. Give one example each of dedifferentiation and redifferentiation.
    3. Which PGR would you use to bolt a rosette plant, and which to close stomata quickly?
    4. Why is abscisic acid called the stress hormone?
    5. What will happen if cytokinin is left out of a tissue-culture medium?

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    Keep learning

    All chapters in Biology - Class 11

    1. 1. The Living World
    2. 2. Biological Classification
    3. 3. Plant Kingdom
    4. 4. Animal Kingdom
    5. 5. Morphology of Flowering Plants
    6. 6. Anatomy of Flowering Plants
    7. 7. Structural Organisation in Animals
    8. 8. Cell: The Unit of Life
    9. 9. Biomolecules
    10. 10. Cell Cycle and Cell Division
    11. 11. Photosynthesis in Higher Plants
    12. 12. Respiration in Plants
    13. 13. Plant Growth and Development
    14. 14. Breathing and Exchange of Gases
    15. 15. Body Fluids and Circulation
    16. 16. Excretory Products and their Elimination
    17. 17. Locomotion and Movement
    18. 18. Neural Control and Coordination
    19. 19. Chemical Coordination and Integration