Chapter 35: Vascular Plant Structure, Growth, and Development

Overview of Vascular Plants

  • Vascular plants are characterized by their intricate system of organs, including roots, stems, and leaves that facilitate growth and development.

Plant Organs

  • Roots:

    • Functions:
    • Anchoring the plant
    • Absorbing essential minerals and water
    • Storing carbohydrates for later use
    • Types of root systems:
    • Taproot system:
      • Features a single, thick primary root that develops into a deep anchor
      • Lateral roots branch off to improve stability and absorption
    • Fibrous root system:
      • Involves many small roots that spread out in a dense network
      • Helps prevent soil erosion
    • Root structures:
    • Root hairs increase surface area for absorption
    • Mycorrhizal associations enhance mineral uptake

  • Stems:

    • Functions:
    • Bear leaves and buds
    • Support plant structure
    • Facilitate transport between roots and leaves
    • Structure:
    • Composed of nodes (leaf attachment points) and internodes (stem segments)
    • Apical bud: Promotes elongation of the stem
    • Axillary buds: Can develop into lateral branches or flowers
    • Modified stems: Specialized stems exist for unique functions (e.g., rhizomes, tubers)

  • Leaves:

    • Main site of photosynthesis in vascular plants
    • Structure includes:
    • Blade: Flat, broad part of the leaf
    • Petiole: The stalk attaching the leaf to the stem
    • Types of leaves:
    • Simple leaves: Compose of an undivided blade
    • Compound leaves: Made up of multiple leaflets
    • Leaf adaptations: Some leaves have evolved for specific functions beyond photosynthesis (e.g., tendrils, spines)

Plant Tissues

  • Plant tissues are broadly categorized into three types: dermal, vascular, and ground tissues.

  • Dermal Tissue:

    • Serves as a protective outer layer.
    • In nonwoody plants, single epidermis layer
    • Waxy cuticle prevents water loss; periderm replaces epidermis in woody plants
    • Guard cells: Regulate gas exchange
    • Trichomes: Reduce water loss and offer protection

  • Vascular Tissue:

    • Facilitate transport:
    • Xylem: Conducts water and minerals upwards
    • Phloem: Transports sugars from leaves to rest of plant
    • Stele: The vascular cylinder of roots/stems; varies by species

  • Ground Tissue:

    • Cells that are neither dermal nor vascular, contribute to storage, photosynthesis, and support.
    • Pith: Internal to vascular tissue
    • Cortex: External to vascular tissue

Cellular Differentiation

  • Parenchyma Cells:
    • Thin cell walls, large vacuoles, play a major role in metabolic activities
  • Collenchyma Cells:
    • Provide support to young plant parts with unevenly thickened walls; flexible support
  • Sclerenchyma Cells:
    • Rigid, lignin-containing cells for structural support; may be dead at maturity
    • Sclereids: Boxy, irregular shapes
    • Fibers: Long, slender, tapered cells

Growth Mechanisms

  • Meristems: Regions where cell division occurs, essentially plant stem cells.
    • Apical meristems: Located at root and shoot tips; responsible for primary growth
    • Lateral meristems: Allow for thickness growth; include vascular cambium (adds xylem/phloem) and cork cambium (replaces epidermis with periderm)
  • Primary Growth: Involves elongation of roots and shoots, allowing plants to grow taller and develop leaves for photosynthesis.