10.2

Topic Overview

  • Focuses on Plant Reproduction and Development.

  • Important chapters:

    • Chapter 35: Introduction to plant structure, growth, and organ systems (Sections 35.1 - 35.5).

    • Chapter 38: Processes of reproduction.

Plant Structure and Tissue Systems

  • Plants are made up of cells, tissues, and organs.

    • Dermal Tissue System: Protective layer, includes:

    • Epidermis: Outermost layer.

    • Cuticle: Waxy layer protecting stems and leaves.

    • Periderm: Replaces epidermis in secondary growth for woody plants.

    • Guard Cells: Allow for gas exchange.

    • Trichomes: Hair-like projections that reduce water loss, reflect light, and deter pests.

    • Vascular Tissue System: Involved in transport, includes:

    • Xylem: Conducts water.

    • Phloem: Transports photosynthates (sugars).

    • Ground Tissue System: Provides storage, support, and photosynthesis, includes:

    • Pith: Inner layer of storage.

    • Cortex: Outer layer for storage and support.

Plant Cells

  • Parenchyma Cells: Most metabolic functions, flexible walls, can differentiate.

  • Collenchyma Cells: Provide support, flexible, living cells.

  • Sclerenchyma Cells: Thickened, dead at maturity, provide rigidity. Types include:

    • Sclereids and Fibers.

Vascular Tissues

  • Xylem Types:

    • Tracheids: Long, narrow cells, dead at maturity,

    • Water moves through pits.

    • Vessel Elements: Shorter, wider cells aligned end-to-end, dead at maturity.

  • Phloem Types:

    • Sieve-tube Elements: Alive but lack certain organelles.

    • Companion Cells: Metabolically support sieve-tube elements.

Plant Growth

  • Meristems: Regions of active cell division contributing to growth.

    • Apical Meristems: Located at tips for vertical growth (primary growth).

    • Lateral Meristems: Enable secondary growth for girth increase (vascular cambium and cork cambium).

  • Primary Growth in Roots:

    • Zones of Growth:

    • Zone of Division, where new cells are generated

    • Zone of Elongation, new cells elongate

    • Zone of Differentiation, cells get specific functions

    • The protoderm gives rise to the epidermis, ground meristem becomes cortex, procambium develops vascular cylinder.

Primary Growth in Shoots

  • Derived from SAM; branching occurs from axillary buds.

  • Leaf primordia develop from the sides of the SAM.

Secondary Growth

  • Increases the diameter of woody plants through lateral meristems.

  • Involves the production of secondary xylem and phloem, cork cambium creates periderm.

  • Growth Rings: Seen in secondary xylem from early and late wood growth throughout seasons.

  • Early Wood: Produced during spring, characterized by larger vessel elements that allow for efficient water transport.

  • Late Wood: Formed in summer, with smaller and thicker-walled vessel elements, providing structural support.

Further distinguishing wood types are:

  • Sapwood: The outer, living layer of the xylem, which conducts water and nutrients. It is typically lighter in color.

  • Heartwood: The inner, non-conducting part of the xylem, often darker, as it consists of dead cells that provide structural support and store metabolic compounds.

  • Bark is all tissues outside the vascular cambium

Summary of Plant Developmental Stages

  1. Growth: Irreversible increase in size.

  2. Morphogenesis: Formation of tissues and organs.

  3. Differentiation: Specialization of cells.

Genetic Control of Flowering

  • Transition from vegetative to reproductive growth influenced by environmental cues (light, temperature) and hormonal signals.

  • ABC Model: Explains flower formation based on gene interaction:

    • A genes: Sepals

    • B genes: Petals and stamens

    • C genes: Carpels