AA

Overview of Plant Anatomy and Morphology

Plant Anatomy

  • Core principle to remember: Structure correlates to function
  • Overview focus: internal structure and how it supports external function
  • Key idea from Page 2: Plant Anatomy (internal structure) vs Plant Morphology (external structure) vs Plant Physiology (function & processes)
  • Levels of study in anatomy: Cells, tissues, organs (inside the plant); focus is on microscopic to macroscopic features
  • Tools used in the study:
    • Microscopy and staining for anatomy and histology
    • Naked eye and hand lens for morphology
    • Sensors and lab experiments for physiology
  • Relationships to other topics: anatomy informs morphology and physiology; foundational principles include cellular organization and tissue specialization
  • Ethical, philosophical, or practical implications: understanding structure-function relationships informs breeding, forestry, agriculture, and ecosystem management

Plant Cells

  • Plant cells are the basic building blocks of the plant body
  • Cells can specialize in form and function to support tissue and organ-level roles
  • By combining into tissues, cells support each other and the whole plant
  • Levels of organization (from smallest to largest): atoms → molecules → cells → tissues → organs → whole plant → population

Cell Theory (Prokaryotes vs Eukaryotes context)

  • All living things are made of cells
  • Cells are the smallest working units of life
  • All cells arise from pre-existing cells via cell division

Cytology and Histology

  • Cytology: the study of cells
  • Histology: the study of tissues (groups of cells with a common function)
  • In plants, cells of the same function and origin make up tissues

Two Types of Cells (Cell Typing)

  • Prokaryotic cells: simple cells without a nucleus (example: bacteria)
  • Eukaryotic cells: complex cells with a nucleus (example: plant and animal cells)

Plant Cell Features (common organelles)

  • Golgi apparatus and Golgi vesicles
  • Endoplasmic reticulum:
    • Rough ER (with ribosomes)
    • Smooth ER (no ribosomes)
  • Nucleus and nucleolus
  • Large central vacuole
  • Chloroplasts (site of photosynthesis)
  • Amyloplasts (starch storage)
  • Mitochondrion (energy production)
  • Ribosomes (protein synthesis)
  • Cell wall and cell membrane
  • Cytoplasm
  • Additional inclusions: raphides (needle-like crystals), druse crystals, other storage crystals
  • 4D cell structure depiction in Armstrong (2001) reference (illustrative context)

Cell Types and Tissue Formation

  • A group of tissues builds an organ
  • Organology: study of plant and animal organs
  • Organs of related functions form organ systems
  • Organ systems assemble into an organism

Plant Tissues

  • All plant organs (roots, stems, leaves) are made of three major tissue types:
    1. Dermal tissue – the outermost layer
    2. Vascular tissue – conducting tissue for transport
    3. Ground tissue – bulk of inner tissues
  • Individual organization in organs:
    • Dermal tissue forms epidermis (outer skin-like layer)
    • Vascular tissue conducts water and nutrients
    • Ground tissue handles metabolism, storage, and support

Plant Organs and Tissues (Structure and Function)

  • Roots, Stems, Leaves are the primary organs organized by dermal, vascular, and ground tissues
  • Dermal Tissue: Epidermis; in stems/leaves includes cuticle (waxy layer to prevent water loss) and trichomes (hairs); root epidermis includes root hairs for water and nutrient absorption
  • Vascular Tissue: Xylem (water and mineral transport from roots to other parts); Phloem (dissolved sugars from leaves to the rest of the plant)
  • Ground Tissue: Bulk tissue for metabolism, storage, and support

Vascular Tissue in Trees (Practical Layout)

  • Vascular tissue is located on outer layers of the tree
  • Structure includes bark, phloem, vascular cambium, wood (xylem)
  • Girdling (cutting around a tree) damages phloem and xylem and can kill the tree

Stem Anatomy (General Concept)

  • The stem is the central axis, usually above ground, connecting roots, leaves, and flowers
  • Main woody stem is called the trunk
  • Stem function: mechanical support and conduit between roots and shoots
  • Parts of a stem (eight distinct parts; six elements and two organs):
    • Elements: nodes, internodes, terminal/apical bud, lateral/axillary bud, petiole, pedicel
    • Organs: leaves, flowers
  • Node: region of active division where buds, leaves, aerial roots, and branches originate
  • Internode: distance between two successive nodes
  • Terminal (apical) bud: tip-growth, always dividing to drive growth
  • Lateral (axillary) bud: develops from the axil between stem and leaf; can give rise to new shoots
  • Petiole: stalk connecting a leaf to the stem; leaves with petioles are called petiolate; leaves without are sessile
  • Pedicel: stalk that attaches an individual flower to an inflorescence; sessile flowers lack a pedicel
  • Leaves: lateral appendages arising from nodes; typically green
  • Flowers: reproductive organs and highly variable in shape and size

Petiole vs Pedicel vs Peduncle (Key Terms)

  • Petiole: leaf stalk
  • Pedicel: stalk of a single flower in an inflorescence
  • Peduncle: stalk supporting an inflorescence or a cluster of flowers
  • Additional related terms: stipule, rachis, stipe, etc. (referenced in the slide for broader stem anatomy vocabulary)

Leaves

  • Leaves are thin, flat organs; main lateral appendages from nodes
  • Typical leaf parts: leaf base, axil, stem, midrib, margin, tip, vein, petiole, venules, leaf blade (lamina)

Plant Morphology (External Form and Appearance)

  • Focus: external form, shape, and appearance of plants
  • Components studied: roots, stems, leaves, flowers, fruits, seeds

Root Structure (Morphology of Roots)

  • Roots anchor the plant and absorb water and minerals
  • Root types based on environment and development:
    • Taproot system: vertical main root from the embryo (radicle) with lateral root hairs; present in all dicots (examples: mango, carrot, radish)
    • Adventitious root system: roots developing from non-radicle parts (usually stems or leaves); common in monocots where the taproot is short-lived (examples: grass, sugarcane, corn)
  • Adventitious root subtypes based on origin:
    • Fibrous roots: slender, branched from stem (e.g., grass, rice)
    • Foliar roots: arise from injured leaf veins or petioles; can give rise to new plants (foliar buds)
    • True adventitious roots: lateral buds from stem nodes/internodes
  • Root modifications (functional and mechanical):
    • Based on Physiological Functions: storage roots, aerial (epiphytic) roots, assimilatory (photosynthetic) roots, reproductive roots, respiratory roots (pneumatophores), epiphytic roots (velamen), saprophytic roots (mycorrhizal association), parasitic roots (haustorial)
    • Based on Mechanical Functions: prop roots (support from aerial branches), stilt roots (oblique/diagonal support), buttress roots (base support), climbing roots (aid climbing), contractile roots (adjust depth via contraction/swelling), floating roots (support floating plants), root-thorns (reduced water absorption in dry environments)
  • Important comparison:
    • Prop roots emerge from stems and grow vertically into soil for additional support
    • Stilt roots emerge from lower stem nodes and grow obliquely for stability in soft/wet soils
    • Buttress roots are horizontal planks that provide base support

Stem Structure (Detailed)

  • The stem serves as the central axis; connects roots, leaves, and flowers; provides mechanical support
  • Variation: unbranched (e.g., palms) vs branched (e.g., roses)
  • Stem anatomy differs between Dicots and Monocots (stem and root anatomies vary between these groups)

Leaves (Detailed Parts)

  • Typical leaf parts: petiole, leaf base, leaf blade/lamina
  • Leaves serve as primary sites for photosynthesis and gas exchange (context from morphology)

Reproductive Organs – Flower

  • Flowers are the reproductive part of flowering plants
  • They are the most colorful and variable organ among plant species

Seed Structure and Function

  • What is a seed?
    • An embryo embedded in nourishing tissue and seed coat; when planted, it grows into a seedling
    • A matured ovule containing an embryo and nutritive tissue enclosed by a protective seed coat
  • Basic parts of a seed:
    • Seed coat (testa) protects the seed
    • Embryo: includes radicle (future root), plumule (future shoot), hypocotyl (future stem)
    • Food storage tissue: endosperm (in monocots often) or cotyledons (in dicots store food)
  • Hilum: a scar on the seed coat where the seed was attached to the ovary wall
  • Micropyle: small pore in the seed coat through which water enters during germination
  • Special structures for some seeds: various seed coat adaptations and storage tissues (illustrated in examples like corn and bean seeds)
  • Dormancy of seeds:
    • A state in which seeds do not germinate despite suitable conditions
    • Causes include hard seed coat impermeability and lack of enzyme activity required for germination
    • Several causes listed (10 common factors total):
      1) Light requirement
      2) Temperature extremes
      3) Hard seed coat
      4) After-ripening period (embryo not mature at shedding)
      5) Germination inhibitors present in seed coat or seed
      6) Immature embryo
      7) Impermeability to water
      8) Impermeability to oxygen
      9) Mechanically resistant seed coat
      10) Presence of concentrated solutes
  • Factors breaking dormancy (to enable germination):
    • Natural methods:
      1) Favorable environmental conditions (moisture and temperature)
      2) Weathering of seed coats (soil microbes, temperature changes or passage through animal digestion)
      3) Completion of after-ripening (embryo matures over time)
      4) Leaching of inhibitors (rainwater/irrigation washes inhibitors away)
      5) Inactivation of inhibitors (cold, heat, or light exposure)
      6) Production of growth hormones (gibberellins counteract inhibitors)
    • Artificial methods:
      1) Scarification (physical/chemical weakening of seed coat; filing, chipping, abrasives)
      2) Hot water treatment (remove surface inhibitors)
      3) Temperature treatments (controlled cold or heat exposure)
      4) Hydraulic pressure (short-term high pressure to weaken coat)
      5) Acid treatment (concentrated sulfuric acid to dissolve part of the coat)
  • Seed germination (definition and stages):
    • The process by which a dormant seed begins to grow into a new plant
    • Involves imbibition (water uptake), metabolic activation, and breaking out of the seed coat
    • Stages of germination:
      1) Imbibition – water uptake and seed swelling; enzyme activation
      2) Metabolic activation – breakdown of stored reserves (cotyledons or endosperm)
      3) Radicle emergence – first root emerges to anchor and absorb water
      4) Plumule emergence – shoot develops into stem and leaves
      5) Development – roots deepen, leaves photosynthesize; seedling establishes
      6) Environmental factors influence germination (water, oxygen, temperature, sometimes light)
  • Types of Germination (epigeal vs hypogeal)
    • Epigeal germination: cotyledons are raised above ground due to elongation of the hypocotyl
    • Hypogeal germination: cotyledons stay below ground; primarily observed in many monocots and some dicots
    • Nomenclature explanation: hypogeal means below ground; epigeal means above ground
  • Vivipary: a special type of germination where seeds germinate while still attached to the parent plant (notably in mangroves)

Seed Types: Gymnosperms vs Angiosperms

  • Seed-Producing Plants are broadly classified into two main groups:
    • Gymnosperms: have naked seeds typically found in cones
    • Angiosperms: have seeds enclosed within fruits and are characterized by flowers
  • Visual contrasts:
    • Gymnosperm seeds are exposed (naked) on scales of cones
    • Angiosperm seeds develop inside fruits and are associated with flowers
  • Fruit and seed relationships visuals (descriptions from slides):
    • Dry fruit vs fleshy fruits (pericarp layers: exocarp, mesocarp, endocarp)
    • Ovary development and receptacle integration influence fruit type
    • False fruits and special fruit types illustrated (e.g., aggregate fruits)
  • Seed anatomy recap:
    • A seed typically consists of seed coat, embryo, and a food storage area (endosperm or cotyledons)
    • Seed coat (testa) protects seed from damage; endosperm or cotyledons provide nourishment; hilum and micropyle are key entry/attachment structures

Seed Structure – Part Functions Recap

  • Endosperm or cotyledons store reserve food for the developing embryo
  • Testa (seed coat) protects the seed
  • Plumule develops into the shoot; radicle develops into the root
  • Embryo components include epicotyl, hypocotyl, and cotyledons
  • In monocots, endosperm often serves as the primary food storage; in dicots, cotyledons store food
  • Special seed structures help with water entry (micropyle) and attachment (hilum)

Seed Dormancy and Germination (Summary)

  • Dormancy protects seeds until conditions are favorable
  • Breaking dormancy is essential for propagation
  • Natural and artificial methods provide practical ways to synchronize germination with environmental conditions
  • Germination is the bridge from seed to seedling; timing and success depend on environmental factors and seed biology

Connections to Theory and Practice

  • The structure-function principle underpins all anatomy and morphology discussions
  • Understanding tissue organization informs how plants transport water, nutrients, and sugars (xylem vs phloem) and how organs coordinate growth
  • Seed biology informs forestry, reforestation, and crop systems through seed quality, dormancy behavior, and germination requirements
  • Practical implications include pruning for girdling effects, breeding for desirable stem, root, or leaf structures, and managing seed storage and germination for agriculture

Quick Reference – Key Terms and Concepts

  • Dermal tissue, vascular tissue, ground tissue
  • Epidermis, cuticle, trichomes, root hairs
  • Xylem, Phloem, cambium
  • Cortex, pith
  • Nodes, internodes, apical/terminal bud, axillary/lateral bud
  • Petiole, Pedicel, Peduncle
  • Leaves, Leaf base, Blade, Midrib, Veins, Margin
  • Flower, Reproductive organs
  • Seed coat (testa), Embryo, Radicle, Plumule, Hypocotyl, Epicotyl, Cotyledons, Endosperm, Hilum, Micropyle
  • Dormancy, Scarification, Stratification, After-ripening, Gibberellins
  • Epigeal vs Hypogeal germination
  • Vivipary (germination while still on the parent plant)
  • Gymnosperms vs Angiosperms, Dry vs Fleshy fruits