Lecture Outline: Plant Structure and Growth

Open PDF Version
  1. Classification of Plants and Angiosperms
    1. Plants are a true clade/monophyletic taxon
    2. Major Plant Groups
      1. Nonvascular plants (also called bryophytes)
      2. Vascular plants (contain vessels)
        1. Seedless vascular plants (e.g., the ferns)
        2. Seeded plants
          1. Gymnosperms (naked seed, e.g., conifers)
          2. Angiosperms (chambered seed, flowering plants)
            1. Hallmarks (The three Fs): Flowers, double fertilization, fruit
            2. Most successful plants; most living plant species are angiosperms
    3. Angiosperm Subdivisions: Monocots vs. Eudicots
      1. Cot part means cotyledon (seed leaf)
      2. Cotyledon function: transfers nutrients to the embryo
      3. Monocots: One cotyledon
      4. Eudicots (Dicots): Truly two cotyledons
    4. Key Differences (Comparison)
      1. Embryo: One cotyledon (Monocot) vs. Two cotyledons (Eudicot)
      2. Leaf Venation (veins pattern)
        1. Monocots: Typically parallel veins (e.g., corn/grasses)
        2. Eudicots: Highly branched or netlike pattern
      3. Vascular Bundles in Stems (cross-section)
        1. Monocots: Scattered (dispersed) throughout the stem
        2. Eudicots: Arranged in a circle
      4. Root System
        1. Monocots: Fibrous root system (no single taproot); branches are uniform
        2. Eudicots: Possess a large taproot, mainly for anchoring
      5. Pollen Grain (microscopic): Monocots typically single opening; Eudicots three openings
      6. Flower Petals: Monocots multiples of three; Eudicots multiples of four or five
  2. Basic Anatomy and Modified Structures
    1. Body Composition
      1. Shoot system (above ground): Consists of stems, buds, flowers, leaves
      2. Root system (below ground): Anchoring and water/nutrient absorption
    2. Shoot System Components
      1. Leaves: Specialized organs for photosynthesis
        1. Stem-like part of leaf is the petiole
        2. Shoots can be: Vegetative (leaves, for growth) or Reproductive (flowers)
      2. Buds: Sites of new growth
        1. Apical buds: On the very ends (apex/tip) of shoots
        2. Axillary buds: At branch points (*nodes*/axle)
      3. Internode: Part of shoot between two nodes
    3. Root Structure and Function
      1. Main function: Allowing water and dissolved minerals to enter the plant
      2. Absorption achieved via root hairs (microscopic projections/microvilli) on individual cells
    4. Exceptional/Unusual Structures (Modified Organs)
      1. Unusual Roots
        1. Storage roots (e.g., radish): Bulbous, store nutrients
        2. Pneumataphores (air roots): Modified roots for acquiring oxygen in waterlogged soil
        3. Strangling aerial roots: Adventitious roots (growing above ground and downward)
      2. Unusual Stems
        1. Rhizomes: Underground, horizontal stems (name means root, but it is a stem)
        2. Tubers (e.g., potato): Underground storage stems
        3. Stolons: Horizontal, above-ground stems (can form new plants/clones)
      3. Modified Leaves
        1. Spines (e.g., cactus): Non-photosynthetic, modified for protection/water retention
        2. Tendrils: Modified for attachment and support (coil and drag the plant)
        3. Reproductive leaves: Modified for asexual reproduction (producing clones)
        4. Storage leaves (e.g., onion): Store nutrients underground
  3. Plant Tissues and Cell Types
    1. Three Major Tissue Types
      1. Dermal tissue: Outer covering (dermis means skin)
      2. Vascular tissue: Contains tube-like vessels (purple part in cartoon)
      3. Ground tissue: Catchall category, fills space between dermal and vascular tissue
    2. Cell Types Based on Toughness (Enkma Tissues)
      1. Parenchyma cells (Least tough): Thin-walled, primary function is photosynthesis (e.g., mesophyll)
        1. Remain alive at functional maturity
      2. Collenchyma cells (Intermediate toughness): Thicker cell walls, provide structure (e.g., green stem)
        1. Remain alive at functional maturity
      3. Sclerenchyma cells (Most tough): Thickest cell walls, rich in lignin (lignified)
        1. Provide structure and protection
        2. Die at functional maturity
  4. Vascular Tissue Structure and Transport
    1. Vessels and Sap
      1. Xylem: Conducts water and dissolved minerals (thin sap)
      2. Phloem: Conducts sugar (highly concentrated, thick/viscous sap)
    2. Xylem Composition (Dead at Maturity)
      1. Made of tracheids (smaller diameter) and vessel elements (larger diameter)
      2. Cells die at functional maturity to function as hollow structures for water flow
      3. Water passes through perforation plates (vessels) or pits (tracheids)
    3. Phloem Composition (Alive at Maturity)
      1. Made of sieve-tube elements
      2. Connect via sieve plates (full of holes)
      3. Sieve-tube elements must remain alive at functional maturity for active transport (sugar movement)
      4. Kept alive by neighboring companion cells
  5. Plant Growth and Development
    1. Growth Types and Meristems
      1. Most plants exhibit indeterminate growth (grow until death)
      2. Growth occurs at meristems (sites where new material is added; juvenile tissue)
    2. Primary vs. Secondary Growth
      1. Primary Growth: Increase in length. Occurs first, at primary meristems (apical/axillary)
      2. Secondary Growth: Increase in diameter/width/girth. Occurs after primary growth
    3. Secondary Growth via Lateral Meristems (Cambia)
      1. Lateral meristems develop after primary growth has occurred in that region
      2. Vascular cambium (red cylinder): Produces secondary xylem (inward) and secondary phloem (outward)
      3. Cork cambium (blue cylinder): Produces cork/bark (exterior structures)
    4. Secondary Xylem Accumulation
      1. Secondary phloem is sloughed off/worn away (does not accumulate thickness)
      2. Secondary xylem is produced inward and accumulates, forming tree rings (wood)
      3. Heartwood (older xylem) is darker, clogged with resin, providing support (no water conduction)
      4. Sapwood (newer xylem) is functional for water conduction
      5. Girdling (damaging vascular cambium all the way around) kills the tree
    5. Root Tip Growth (Primary Growth Example)
      1. Root cap: Toughened, dead cells protecting the tip from abrasion
      2. Zone of cell division (proliferation): Site of apical meristem where new cells are created by mitosis
      3. Zone of elongation: Cells grow longer in one direction, increasing root length
      4. Zone of differentiation: Cells mature into specialized tissue types (e.g., vascular tissue, root hairs)
    6. Regulation of Shoot Growth
      1. Apical meristem dominance: Apical bud signals inhibit axillary buds, prioritizing length/height
      2. If the apical meristem is destroyed (nipped), axillary buds take over, resulting in branching
      3. New root branches erupt from the vascular cylinder to connect to existing vessels
  6. Tissue Arrangement in Organs
    1. Leaf Structure (Cross-section)
      1. Epidermis: Outer layer waterproofed by waxes (lipids)
      2. Stomata (openings): Allow CO2 entry for carbon fixation; formed by guard cells
      3. Mesophyll: Interior tissue for photosynthesis (mostly parenchyma cells)
    2. Root Tissue Arrangement (Cross-section)
      1. Eudicot Root: Vascular tissue centralized; Xylem forms an X-like structure in the center
      2. Monocot Root: Vascular bundles spread out in the center core
    3. Stem Tissue Arrangement (Cross-section)
      1. Eudicot Stem: Vascular bundles arranged in a ring
      2. Monocot Stem: Vascular bundles dispersed throughout the stem
      3. In all stem bundles: Phloem faces outward (superficial); Xylem faces inward (deep)