SP 25 Ch 28_student

Vascular Plant Structure and Function

• Chapter Overview

  • Dr. Koning, February 27, 2025

Learning Objectives

• LO 28.1: Identify roots, stems, and leaves in unknown plant images and explain their functions.

• LO 28.2: Hypothesize the adaptive significance of root, stem, and leaf structures based on plant habitat.

• LO 28.3: Describe stomata's role in gas exchange (CO2/O2) and their response to environmental changes.

Structure Function Relationship in Vascular Plants

Organ Level

• Leaves: Provide surface area for photosynthesis.

• Stems: Support and elevate leaves for better light access.

• Roots: Anchor the plant and absorb water and minerals.

Tissue Level

• Vascular Tissue: Supports and transports materials.

• Dermal Tissue: Protects plant organs.

• Ground Tissue: Where photosynthesis occurs (contains chloroplasts).

Cellular Level

• Photosynthetic Cells: Possess chloroplasts for energy production.

• Tube-shaped Cells: Transport resources efficiently.

• Root Hair Cells: Increase the surface area for greater absorption capacity.

Plant Form and Function

• Growth patterns follow a repetitive sequence of stem-leaf-bud.

• Development is genetically determined and adaptive through natural selection.

• Greater body form diversity compared to animals due to fixed growth patterns in one location.

Hierarchical Organization of Plants

• Composed of:

  • Organs: Multiple tissues performing specific functions.

  • Tissues: Groups of cells that carry out specialized roles.

  • Cells: The fundamental life unit, responsible for specific functions.

Plant Organs

• Reflect adaptations for both above and below ground resource acquisition.

• Root System: Comprised of roots;

• Shoot System: Comprises stems, leaves, and flowers.

Roots

• Functions:

  • Anchoring the plant in soil.

  • Absorbing water and minerals.

  • Storing carbohydrates.

Types of Root Systems

• Taproot System:

  • Main vertical root; prevents toppling (e.g., tall plants).

  • Lateral roots branch out for absorption.

• Fibrous Root System:

  • Network of small roots; stabilizes small or trailing plants.

Adaptations for Water Absorption

• Root Hairs: Increase surface area for absorption.

• Mycorrhizal Associations: Symbiotic relationships with fungi enhancing nutrient uptake.

Stems

• Structure:

  • Consist of nodes (leaf attachment) and internodes (stem segments).

• Functions: Elongation and orientation for maximizing photosynthesis.

Bud Types

• Apical Bud:

  • Located at shoot tip; facilitates elongation.

• Axillary Bud:

  • Located at leaf-branch angle; can develop lateral branches.

Modified Stems

• Rhizomes: Horizontal underground shoots.

• Stolons: Horizontal shoots above ground for asexual reproduction.

• Tubers: Food-storage structures at rhizome ends.

Leaves

• Main Function: Typically the primary site for photosynthesis.

• Other Functions: Gas exchange, heat dissipation, and defense.

Leaf Structure

• Components:

  • Flattened blade for maximum surface area.

  • Petiole for attaching leaf to stem.

• Vein Patterns: Differ in monocots (parallel) versus eudicots (branched).

Specialized Leaf Adaptations

• Tendrils: Support climbing plants.

• Spines: Cactus spines for protection; stems conduct photosynthesis.

• Storage Leaves: Modified leaves that store food.

Plant Tissue Systems

• Composed of three primary systems:

  • Dermal: Outer protective covering.

  • Vascular: Facilitates material transport and mechanical support (xylem and phloem).

  • Ground: Functions include storage, photosynthesis, and support.

Dermal Tissue Details

• Epidermis: The outer cell layer in nonwoody plants, may have cuticles preventing water loss.

• Periderm: Replaces epidermis in older woody stems and roots.

Vascular Tissue Function

• Xylem: Conducts water/minerals upwards.

• Phloem: Transports sugars from production sites.

Ground Tissue Overview

• Pith and Cortex:

  • Pith: Internal to vascular tissue.

  • Cortex: External to vascular tissue; involved in storage and transport.

Plant Cells

Major Types of Cells

• Parenchyma: Flexible walls, multifunctional, and capable of cell division.

• Collenchyma: Unevenly thickened walls providing flexible support.

• Sclerenchyma: Rigid with thick, lignified walls; usually dead at maturity.

• Water-Conducting Cells: Tubular and elongated for efficient transport (e.g., tracheids, vessel elements).

• Sugar-Conducting Cells: Sieve-tube elements found in phloem, alive at maturity.

Growth Mechanisms

Meristems

• Indeterminate Growth: Allows continuous growth throughout the plant's life, driven by meristems.

• Apical Meristems: Responsible for primary growth in length.

• Lateral Meristems: Responsible for secondary growth in circumference (vascular cambium and cork cambium).

Primary Growth Zones

• Zones of Growth:

  • Cell division, elongation, differentiation in root and shoot tips.

Secondary Growth Insights

• Characteristics:

  • Common in gymnosperms/eudicots; results in increased stem diameter.

Flowering and Plant Lifespan

Transition to Reproductive Growth

• Involves environmental cues and internal signals.

• Categorized into annuals, biennials, and perennials based on lifecycle duration.

Summary of Growth Regions

Root System

• Covered by a root cap; growth occurs in three overlapping zones.

  • Root hairs significantly increase absorption area.

  • Endodermis serves as a selective barrier for nutrient uptake.

Shoot System

• Shoot apical meristem leads growth in length.

• Axillary buds allow for branching once apical dominance is removed.

Vascular Cambium and Cork Cambium Effects

Vascular Cambium Function

• Produces secondary xylem (wood) and phloem; responsible for bulk plant growth in diameter.

Cork Cambium Function

• Produces protective cork layer; essential for water and gas impermeability.

Summary of Structures and Functions

• Heartwood/Sapwood: Central wood layers cease transport/actively transport materials.

• Bark: Includes all external layers, necessary for plant protection and functionality.