Plants have specialized structures that perform essential functions for survival and reproduction.
The primary structural components of plants include roots, stems, and leaves.
Developmental Plasticity
Definition: The ability of a plant to alter its structure in response to environmental conditions.
Example: Fanwort can be viewed as either an invasive species or an attractive aquarium plant.
Developmental plasticity is more prominent in plants than animals. This allows plants to adapt to various environments.
Basic Plant Organs
Three Basic Organs:
Roots: Anchors the plant, absorbs water and minerals, stores nutrients.
Stems: Support structure for leaves; contains nodes and internodes.
Leaves: Main site for photosynthesis; typically structured with a flattened blade and petiole.
Root System vs. Shoot System:
Roots depend on sugars from photosynthesis, while shoots rely on water and minerals contributed by roots.
Roots
Functions of Roots:
Anchor the plant.
Absorb minerals and water, primarily through root hairs.
Store organic nutrients.
Types of Root Systems:
Taproot System: One main vertical root with lateral roots.
Fibrous Root System: Many thin lateral roots, typical of grasses and some angiosperms.
Modified Roots
Types:
Prop Roots: Provide additional support.
Storage Roots: Store carbohydrates.
Buttress Roots: Stabilize tall plants.
Pneumatophores: Specialized roots for gas exchange in waterlogged soil.
Stems
Structure: Composed of nodes, internodes, axillary and apical buds.
Functions:
Support leaves and reproductive structures.
Conduct materials between roots and shoots.
Modified Stems
Examples:
Rhizomes: Horizontal underground stems.
Bulbs: Storage structures.
Stolons: Above-ground runners.
Tubers: Swollen storage tips of rhizomes.
Leaves
Functions: Primary site for photosynthesis.
Structure:
Blade: Flat part of the leaf.
Petiole: Stalk connecting leaf to stem.
Modified Leaves
Examples include:
Tendrils: Support climbing plants.
Spines: Protect plants (e.g., cacti).
Storage Leaves: Store water and nutrients.
Reproductive Leaves: Produce new plants (e.g., Mexican hat plant).
Tissue Systems
Dermal Tissue: Protective outer covering.
Epidermis: Consists of a single layer of cells; covered by cuticle to reduce water loss.
Vascular Tissue: Conducts water, minerals, and nutrients.
Xylem: Transports water and dissolved minerals.
Phloem: Transports sugars and organic nutrients.
Ground Tissue: Functions in support, storage, and photosynthesis.
Major Plant Cell Types
Parenchyma: Thin-walled, versatile; involved in metabolic functions and healing.
Collenchyma: Flexible support for young stems; thickened cell walls.
Sclerenchyma: Rigid, dead at maturity; provides structural support (includes fibers and sclereids).
Growth and Development
Meristematic Tissue: Regions of active cell division that allow growth.
Apical Meristems: Located at tips; responsible for primary growth in height.
Lateral Meristems: Include vascular cambium and cork cambium; responsible for secondary growth (thickness).
Indeterminate Growth: Continuous growth throughout life; common in many plants.
Determinate Growth: Growth that stops after reaching a certain size, typical in some plant organs.
Leaf Anatomy
Epidermis: Contains stomata for gas exchange and is covered by cuticle for water retention.
Mesophyll: Ground tissue between the upper and lower epidermis; contains palisade and spongy mesophyll for photosynthesis and gas exchange.
Vascular Bundles: Veins that transport water and nutrients throughout the leaf.
Summary
Understanding plant structure involves knowledge of basic organs (roots, stems, leaves) and their functions, types of cells and tissues, as well as growth mechanisms. Each part plays a critical role in the overall physiology and adaptability of plants against environmental changes.