angiosperms

Chapter 34: Structure and Growth of Angiosperms

Plant Organization

• Overview of Structures
    - Hierarchical organization: organs and systems
    - Root System
      - Comprises roots of the plant
    - Shoot System
      - Consists of stem and leaves

Surface Area to Volume (SAV) Ratio

• SAV Ratio Calculation for Different Sizes
    - For a cube of dimensions 1 cm x 1 cm:
      - Surface area = 6 cm²; Volume = 1 cm³ → SAV = 6:1
    - For a cube of dimensions 5 cm x 5 cm:
      - Surface area = 150 cm²; Volume = 125 cm³ → SAV = 1.2:1
    - Alternative interpretation of interior surfaces:
      - Important to consider internal structure for overall plant health

Plant Tissue Types

• Meristematic Tissues
    - Undifferentiated cells capable of division
    - Responsible for growth in plants

• Permanent Tissues
    - Differentiated tissues that perform specific functions

• Plant Tissue Systems
    - Ground Tissue
      - Components:
        - Pith: Inner tissue that stores nutrients.
        - Cortex: Outside layer of vascular tissue.
    - Dermal Tissue
      - Components:
        - Cuticle: Protective outer layer.
    - Vascular Tissue
      - Xylem: Conducts water and minerals.
        - Components:
          - Tracheids: Water-conducting cells with lignin.
          - Vessel Elements: Specialized tubes for water transport.
      - Phloem: Transports sugars.
        - Components:
          - Sieve Tube Members: Transport nutrients.
          - Companion Cells: Support sieve elements.

Epithelial and Vascular Organization

• Types of Permanent Cells
    - Parenchyma: Living cells for storage and photosynthesis.
    - Collenchyma: Support for young plants; flexible.
    - Sclerenchyma: Provides rigidity; contains lignin.
      - Fibers: Long, supportive cells; used in textile production.
      - Sclereids: Stone cells found in nuts and seeds.

Root Types and Functions

• Monocots: Fibrous root systems

• Dicots: Taproot systems

• Root Functions
    - Anchoring the plant into the soil
    - Uptake of water from the soil
    - Storage of food molecules
    - Nutrient exchange with the soil

• Root Structural Variations
    - Prop Roots: Provide additional support.
    - Buttress Roots: Enhance stability for tall trees.
    - Pneumatophores: Air roots for oxygen uptake.
    - Aerial Roots: Above-ground roots that gather moisture.
    - Storage Roots: Store nutrients for later use.

Anatomy of Roots

• Root Hairs: Increase surface area for absorption.

• Root Structure
    - Root Cap: Protects root tip.
    - Meristem: Zone of rapid cell division.
      - Quiescent Center: Dormant cells.
    - Primary Meristems
      - Protoderm: Forms the epidermis.
      - Ground Meristem: Forms ground tissue.
      - Procambium: Forms vascular tissues.

• Zones of Root Development
    - Zone of Differentiation: Cells specialize.
    - Zone of Elongation: Cells elongate.
    - Zone of Cell Division: Apical meristem activity.

Shoot System Structure

• Components
    - Stems: Structures that support leaves and flowers.
    - Nodes: Points where leaves attach to the stem.
    - Internodes: Segments of stem between nodes.
    - Apical Meristem: Growth point at the tip of the stem.
    - Axillary Buds: Potential growth points, lay dormant unless activated.
    - Terminal Buds: Primary growing point at the end of the stem.

• Stem Modifications
    - Stolon (Runner): Horizontal stem above ground.
    - Rhizome: Horizontal underground stem.
    - Tubers: Swollen part of underground stem for storage.

Leaf Structure

• Components of Leaves
    - Blade: Broad part of the leaf.
    - Stalk (Petiole): Connects leaf blade to stem.

• Leaf Venation
    - Parallel: Typical of monocots.
    - Reticulate: Typical of dicots.

• Types of Leaves
    - Simple Leaves: Single undivided blade.
    - Compound Leaves: Multiple leaflets.
      - Double Compound Leaves: Leaflets divided into yet smaller leaflets.

• Leaf Anatomy in Dicots
    - Two layers of mesophyll:
      - Spongy Mesophyll: Air spaces for gas exchange.
      - Palisade Mesophyll: Where photosynthesis primarily occurs.
    - Stomata: Regulate gas exchange and water loss.

Plant Growth

• Indeterminate Growth: Plants can grow indefinitely under proper conditions.

• Life History of Plants
    - Annuals: Complete life cycle within a single year.
    - Biennials: Life cycle spans two years.
      - Undergo a period of dormancy during winter.
    - Perennials: Live for multiple years, continuing to grow thereafter.

• Types of Growth
    - Primary Growth: Increases the length of the plant.
    - Secondary Growth: Increases the girth of the plant.

Secondary Growth in Plants

• Lateral Growth
    - Involves formation of vascular cambium.
      - Secondary Xylem: Forms wood and creates growth rings.
      - Secondary Phloem: Contributes to the outer layers.

• Tree Rings: Reflect age and growth conditions.

• Bark Structure
    - Bark = Periderm + Phloem
      - Periderm: Replacement for the epidermis in older stems.
      - Cork Cambium: Formed by layers of phloem.
      - Layers of Periderm: Cork layer providing insulation and waterproofing.

• Heartwood vs. Sapwood
    - Heartwood: Inert central wood, provides structural support.
    - Sapwood: Active in water transportation and nutrient storage.