Plant Structure and Function Notes

Plant Structure & Function

What is a plant?

  • Multicellular

  • Sessile (fixed in one place)

  • Capable of creating their own food through photosynthesis (using sunlight)

Extraordinary Attributes of Plants

  • Plants are extremely diverse but share a basic structural organization.

Longevity

  • The longest-lived plants can exceed lifespans of 4,800 years (e.g., Bristlecone pines).

Height

  • Tallest plants can be around 379 feet (e.g., Coast redwoods).

Weight

  • Heaviest plants can weigh over 3,300 tons (e.g., giant sequoias).

Energy Acquisition

  • Plants capture sunlight and convert it into chemical energy, unlike animals.

Classification of Flowering Plants

  • Flowering plants are grouped into:

    • Monocots: One cotyledon in the embryo.

    • Eudicots (Dicots): Two cotyledons in the embryo; Eudicots are a subgroup of Dicots.

Characteristics of Plant Types

  • Non-vascular Plants (no true roots, stems, or leaves): Algae, mosses.

  • Vascular Plants: Have roots, stems, and leaves, can be further classified into:

    • Angiosperms (makes seeds and has flowers): e.g., sunflowers.

    • Gymnosperms (makes seeds but no flowers): e.g., conifers.

Plant Structure

Three Main Parts

  • Roots: Absorb water/minerals, anchor the plant, and store food.

  • Stems: Provide structural support, position leaves for sunlight, and conduct nutrients.

  • Leaves: Site of photosynthesis, convert sunlight to food.

Monocots vs. Eudicots

Monocots

  • One cotyledon

  • Parallel leaf veins

  • Vascular tissue in scattered bundles

  • Flower parts in multiples of three

  • Fibrous roots

Eudicots

  • Two cotyledons

  • Branching leaf veins

  • Vascular tissue in a ring

  • Flower parts in multiples of four or five

  • Taproot system

Plant Tissues

Types of Tissues

  • Vascular Tissue: Transports water and nutrients (xylem and phloem).

  • Ground Tissue: Bulk of the plant; metabolism occurs here.

  • Dermal Tissue: Protective covering (includes epidermis and guard cells).

Dermal Tissue Functions

  • Epidermal Cells: Forms thin outer layer, reduces water loss via cuticle.

  • Guard Cells: Control openings (stomata) for gas exchange and minimize water loss.

  • Cork Cells: Replace epidermal cells as the plant matures; form bark.

Vascular Tissue

Xylem and Phloem

  • Xylem: Conducts water and minerals from roots to the rest of the plant.

  • Phloem: Transports sugars from photosynthesis to parts of the plant.

Root Functions

Importance of Roots

  • Absorption: Water, minerals, and gases are uptaken.

  • Anchorage: Keeps plants secure in soil.

  • Storage: Starch and water storage for future use.

Types of Root Systems

  • Fibrous Roots: Many similarly sized roots, shallow soil occupation, common in monocots.

  • Taproots: Thicker main roots that go deep, common in eudicots.

Special Root Structures

  • Snorkel Roots: Adaptation of mangroves for gas exchange.

  • Buttress Roots: Stabilize trees in saturated soils.

Functions of Stems

  • Structural Support: Keep the plant upright.

  • Leaf Positioning: Optimize light interception for photosynthesis.

  • Nutrient Distribution: House vascular tissues for transport.

Meristems

  • Growth occurs in regions called meristems: apical (tips) and lateral (sides).

Leaf Structure and Function

  • Leaves convert sunlight into food, with specialized cells for photosynthesis.

Leaf Morphology

  • Variability in shape and size based on environmental adaptations.

    • Sun Leaves: Smaller and thicker, minimize water loss.

    • Shade Leaves: Larger and thinner, maximize light absorption.

Modified Leaves

  • Various adaptations (e.g., spines in cacti, tendrils for climbing).

Water Conservation Mechanisms

  • Cuticle: Waxy layer preventing water loss.

  • Leaf Hairs: Reduce wind speed over leaves, decreasing evaporation.

  • Stomata: Regulated openings for gas exchange, managed by guard cells.

Key Factors for Plant Growth

  1. Sunlight: Energy source.

  2. Water: Essential for chemical reactions.

  3. Air: Provides CO₂ for photosynthesis.

  4. Soil: Source of minerals; consists of minerals, organic matter, air, and water.

Soil and Nutrients

  • Importance of decomposition for nutrient release.

  • Nitrogen fixation through symbiotic bacteria to enrich soil.

  • Crop rotation to maintain soil nitrogen levels.

  • Mineral uptake requires transport proteins in root cells.

Sugar and Nutrient Distribution

  • Phloem: Main food delivery system; operates on a source-to-sink basis (leaves to roots).

  • Mechanism of sugar transportation: loading, osmosis, pressure increase, and unloading.

Maple Syrup Production

  • Seasonal sap movement in trees; collection and processing into syrup.