🌱 Plant Growth & Development – Quick Notes

Growth

Meaning of Growth

  • Irreversible, permanent increase in size of organ, part or cell.
  • Always linked with metabolic activity and use of energy.
  • Leaf expansion = growth.
  • Swelling of wood in water ≠ growth (no metabolism).
Plant Feature

Uniqueness of Plant Growth

  • Plants can grow almost throughout life.
  • Due to meristems present in specific regions.
  • Meristematic cells divide continuously and add new cells.
  • New cells later lose division ability and form permanent tissues.
  • Growth stops when meristematic activity stops.
Open growth: continuous addition of new cells by meristems.
Growth Types

Types of Growth (Summary)

  • Determinate: Stops after a certain size or maturity.
  • Indeterminate: Continues as long as plant is alive and resources are available.
  • Open growth: Same plant shows both determinate and indeterminate growth.
Examples:
– Determinate: leaves, flowers, sunflower plant.
– Indeterminate: roots and stems, vines.
Concept

Open Differentiation

  • Final structure and function of cells is not fixed from the beginning.
  • Cells can still change and differentiate according to their position and environment.
Development

Meaning of Development

  • Development = Growth + Differentiation.
  • Starts from the zygote.
  • Occurs in a definite, ordered sequence of events.
  • Forms roots, stems, leaves, branches, flowers, fruits and seeds.
  • Ends with death after maturation.
Stages

Basic Stages in Development

  • Cell division: increase in cell number.
  • Meristematic cells: undifferentiated, actively dividing cells.
  • Plasmatic growth: increase in protoplasm and cell size.
  • Expansion (elongation): cells elongate, organ length increases.
  • Differentiation: cells become specialised tissues and organs.
  • Maturation: tissues/organs become fully functional.
Later Changes

Aging & Senescence

  • Aging: gradual structural and chemical changes with time.
  • Occurs in whole plant or individual organs.
  • Senescence: final deteriorative phase of aging.
  • Dominated by breakdown (catabolic) processes, irreversible, ends in death of cell/organ/plant.
  • Can occur at whole plant, organ, cell or organelle level.
Abscission

Abscission (Shedding)

  • Natural shedding of leaves, flowers and fruits.
  • Deciduous plants: many leaves fall together in one season.
  • Evergreen plants: leaf fall is slow and continuous.
  • Dead leaves of some herbs may remain attached.
  • Colour change occurs due to chlorophyll breakdown and other pigment formation.
Final Stage

Death

  • Final stage of the plant life cycle.
  • Occurs after prolonged senescence when metabolism stops.
  • Often associated with abscission of non-functional parts.
  • Marks the completion of growth, development and reproduction.