roots,stems, and leaves 2020

Plant Tissues and Structure

Development and Adaptation

• Development of plants highly adaptive to the environment.

• Two major groups of angiosperms:

  • Monocots

  • Eudicots

Hierarchical Organization in Plants

• Plants possess a hierarchical structure:

  • Organs made up of different tissues.

  • Tissues are composed of various cell types.

• Key Definitions:

  • Organ: Collection of several tissue types that perform specific functions.

  • Tissue: Group of cells comprising one or more cell types with specialized function.

Plant Structure

Plant Systems

• Plants consist of two main systems:

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

  • Root System: Anchors the plant and absorbs nutrients.

Roots Functionality

• Roots serve multiple vital functions:

  • Anchoring the plant.

  • Absorbing minerals and water from the soil.

  • Storing carbohydrates.

• Primary Root: First root that develops, branches into lateral roots for enhanced support and absorption.

Root Types

• Taproot System:

  • Common in tall plants; features a primary root.

  • Prevents toppling, with lateral roots handling absorption.

• Fibrous Root System:

  • Present in small or trailing plants; composed of

    • Adventitious Roots: Develop from stems or leaves.

    • Lateral Roots arising from adventitious roots.

Root Structure

• Absorption mainly occurs at root tips:

  • Increase in surface area due to root hairs.

Stems and Leaves Structure

Stem Structure

• Stems consist of:

  • System of nodes (where leaves attach).

  • Internodes (segments between nodes).

• Apical Bud: Causes elongation of young shoots.

• Axillary Bud: Can develop into a lateral branch, thorn, or flower.

Leaves Overview

• Main Functions of Leaves:

  • Photosynthesis.

  • Gas exchange (CO2, O2).

  • Heat dissipation.

  • Defense against herbivores and pathogens.

• Structure includes:

  • Blade: Flattened part.

  • Petiole: Stalk attaching leaf to stem.

Leaf Type Differences

• Monocots vs. Eudicots:

  • Monocots: Parallel vein arrangements.

  • Eudicots: Branching vein structures.

  • Leaf morphology aids in classification.

Tissue Systems in Plants

Tissue Organization

• Each plant organ consists of three main tissue systems:

  • Dermal Tissue: Outer protective layer.

  • Vascular Tissue: Transport system.

  • Ground Tissue: Fills spaces between dermal and vascular tissues.

Dermal Tissue

• In nonwoody plants: Epidermis protects.

  • Cuticle: Waxy coating prevents water loss.

• In woody plants: Periderm replaces older epidermis.

  • Trichomes: Epidermal features aiding water retention and defense.

Vascular Tissue

• Facilitates transport; consists of:

  • Xylem: Conducts water and minerals upward.

  • Phloem: Transports sugars throughout the plant.

• Vascular tissue of roots and stems known as stele.

Growth in Plants

Meristematic Tissue

• Responsible for plant growth:

  • Apical Meristems: Located at tips of roots and shoots; allow for primary growth.

  • Lateral Meristems: Add thickness through secondary growth.

Types of Growth

• Indeterminate Growth: Continues throughout a plant's life.

• Determinate Growth: Ceases at a certain size.

Secondary Growth

• Occurs in woody plants via:

  • Vascular Cambium: Produces secondary xylem and phloem.

  • Cork Cambium: Forms protective outer layer.

Summary of Growth Patterns

Growth Rings and Aging

• Dendrochronology: Study of tree rings helps understand growth patterns and historical climate changes.

• Heartwood vs. Sapwood: As trees age, heartwood stops transporting, while sapwood remains functional.

Cork Cambium and Bark Structure

• Cork cambium produces cork cells that create a protective periderm.

• Lenticels allow for gas exchange in the cork layer.