Plant Tissues

Plant Tissues Lecture Notes

Overview of Main Points

  • Functions of meristematic tissue.
  • Definitions of initials and derivatives in plant cells.
  • Differences between indeterminate and determinate growth with examples.
  • Functions of ground tissues: sclerenchyma, parenchyma, collenchyma.
  • Types of tracheary elements in xylem.
  • Contrasts between xylem and phloem functions.
  • Sieve elements in phloem tissue.
  • Function of trichomes within the dermal tissue system.

Meristematic Tissue

  • Definition & Function: Regions of active cell division, located at tips of stems and roots, responsible for the extension of the plant body.
  • Cell Types:
    • Initials: Cells that remain within meristematic tissue.
    • Derivatives: Cells produced through division that differentiate into specific tissues.
  • Types of Growth:
    • Primary Growth: Responsible for elongation (primarily from apical meristem).
    • Secondary Growth: Increases girth of stems (from vascular & cork cambium).

Growth Types

  • Indeterminate Growth (Plants): Continuous growth throughout life.
  • Determinate Growth (Animals): Growth ceases upon reaching maturity.
  • Examples: Plants can regenerate leaves and branches, whereas animals have a preset growth plan.

Developmental Plasticity

  • Ability of plants to modify morphology in response to environmental stimuli.
  • Differences in leaf structures depending on sunlight exposure (e.g., leaves on sunny vs. shady sides of trees).
  • Developmental plasticity vs. animal behavior (nature vs. nurture).

Plant Development Processes

  • Growth: Irreversible increase in size (cell division and enlargement).
  • Morphogenesis: Development of shape, influenced by genes and environmental stimuli.
  • Differentiation: Cells with identical genetic information become specialized based on position and environmental factors.

Introduction to Plant Tissues

  • Definition of Tissue: Group of similar cells that work together for a common function.
  • Tissue Systems: Groups of tissues organized into functional units. Three systems in plants:
    • Ground Tissue System (parenchyma, collenchyma, sclerenchyma).
    • Vascular Tissue System (xylem and phloem).
    • Dermal Tissue System (epidermis).

Ground Tissue System

  1. Parenchyma:
    • Living cells, thin-walled, flexible, involved in photosynthesis, storage, and regeneration (totipotency).
  2. Collenchyma:
    • Living cells, unevenly thickened walls, support for growing tissue (e.g., celery stalk).
  3. Sclerenchyma:
    • Often dead cells, thick lignified walls, provide structural support (fibers and sclerids).

Vascular Tissue System

Xylem:
  • Function: Main water-conducting tissue, transports minerals.
  • **Cell Types:
    • Tracheids:** Primitive, elongated cells with pitted walls.
    • Vessel elements: More efficient, aligned end to end with perforations.
  • Apoptosis: Xylem cells undergo programmed cell death, leaving hollow structures for transport.
Phloem:
  • Function: Food-conducting tissue, transports sugars and nutrients.
  • Cell Types:
    • Sieve cells: Present in gymnosperms, no sieve plates.
    • Sieve tube elements: Found in angiosperms, stacked in tubes and connected by sieve plates.
  • Companion cells: Support sieve tube elements and keep them alive.

Dermal Tissue System

  • Epidermis: Protective outer layer of young plant parts; regulates gas exchange (stomata with guard cells).
  • Trichomes: Specialized epidermal cells for various functions (e.g., increase root surface area, reflect sunlight, defense against herbivory).
  • Cuticle: Waxy layer minimizing water loss, primarily made of cutin.

Recap of Key Functions

  • Meristematic Tissue: Source of new growth.
  • Ground Tissue: Support and storage.
  • Vascular Tissue: Transport of water, nutrients, and foods.
  • Dermal Tissue: Protection and regulation.