Chapter 28 Plant Structure and Growth

Chapter 28: Plant Structure and Growth

• Are Plants Computers?

  • Romanesco (a cauliflower variant) grows according to a repetitive program.
  • Plant development is highly adaptive and influenced by the environment.

• Angiosperms Overview

  • Angiosperms are crucial primary producers and play significant roles in agriculture.
  • Taxonomists categorize angiosperms into two major clades: monocots and eudicots.

Concept 28.1: Hierarchical Organization in Plants

• Organization of Plants

  • Composed of:
  • Organs: Composed of different tissues for specific functions.
  • Tissues: Groups of cells that perform specialized functions.
  • Cells: The basic unit of life.

• Three Basic Plant Organs

  • Roots: Anchor the plant, absorb water/minerals, and store carbohydrates.
  • Stems: Transport materials and provide support.
  • Leaves: Main sites for photosynthesis, gas exchange, and temperature regulation.

• Connection Between Systems

  • Roots absorb water and minerals; shoots absorb CO₂ and light.
  • The root and shoot systems are interconnected by vascular tissues.

Roots

• Root Functions

  • Anchor plants and absorb nutrients.
  • Root Hairs: Extensions of epidermal cells that increase surface area.

• Root Types

  • Taproot System: Main vertical root with lateral roots (for tall plants).
  • Fibrous Root System: Many thin roots for small or trailing plants (adventitious roots).

• Mycorrhizal Associations

  • Many plants form associations with fungi to enhance mineral absorption.

Stems

• Stem Structure

  • Consists of nodes (leaf attachment points) and internodes (between nodes).
  • Apical Bud: Causes shoot elongation.
  • Axillary Bud: Potential to form lateral branches.

• Modified Stems

  • Rhizomes, Stolons, Tubers: Serve additional functions like propagation and storage.

Leaves

• Leaf Functions

  • Primarily responsible for photosynthesis; also involved in gas exchange and heat regulation.
  • General structure: flattened blade and petiole (stalk).

• Vein Arrangement

  • Monocots: Parallel veins.
  • Eudicots: Branching veins.

Tissue Systems in Plants

• Three Main Tissue Systems
  • Dermal Tissue: Protective outer covering.
  • In nonwoody plants, it consists of the epidermis and sometimes a cuticle.
  • Vascular Tissue: Responsible for transporting materials.
  • Xylem: Conducts water and minerals upward.
  • Phloem: Transports sugars downwards after photosynthesis.
  • Ground Tissue: Non-dermal and non-vascular; involved in storage and photosynthesis.

Common Types of Plant Cells

• Parenchyma: Involved in storage and photosynthesis.
• Collenchyma: Provides support, especially in young stems.
• Sclerenchyma: Offers strength and support, usually dead at maturity.

Vascular Tissue Details

• Xylem Cells

  • Tracheids: Long, thin cells for water movement.
  • Vessel Elements: Form long vessels for efficient water transport.

• Phloem Cells

  • Sieve Cells: Transport sugars in seedless vascular plants and gymnosperms.
  • Sieve-tube Elements: Chains for fluid transport in angiosperms, accompanied by companion cells.

Concept 28.2: Meristems

• Meristem Types
  • Apical Meristems: Located at tips of roots and shoots; root and shoot elongation (primary growth).
  • Lateral Meristems: Increase thickness in woody plants (secondary growth).
  • Vascular cambium and cork cambium.

Concept 28.3: Primary Growth of Roots and Shoots

• Zones of Root Growth

  • Zone of Cell Division, Elongation, Differentiation: Areas in root tip critical for growth.

• Shoot Growing Mechanism

  • Apical meristem allows for leaf development and shoot elongation; axillary buds can develop into lateral shoots.

Concept 28.4: Secondary Growth

• Secondary Growth Characteristics

  • Not present in all plants; includes vascular cambium contributing to wood formation.
  • Xylem Types
  • Early Wood: Thin walls for maximum water conducting.
  • Late Wood: Thicker walls for structural support.

• Bark

  • Consists of all tissues external to the vascular cambium, with cork cells aiding in protection.

Summary of Functionality in Plant Growth

• Growth patterns characterized by cell differentiation controlled by gene expression.

• Environmental cues and internal signals drive the transition to reproductive stages (flowering).

• Overall, plants employ an adaptive hierarchy of organization, utilising specialized structures and tissues to maximize efficiency in resource acquisition and growth.