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					Plant Structure, Growth &
             Development
                        Packet #35
                Chapters #35 & #38
The Plant Body
Introduction
   Genes and the environment affect plant structure.
   Plants exhibit structural responses to their specific
    environment.
       Plasticity
           Explains why no two plants are identical.
               Mangroves and cacti
Introduction II
   Plants are multi-cellular, have organs that are composed of
    different tissue (previously covered), and tissue which are
    composed of different cell types (previously covered).
Roots, Stems & Leaves
Introduction
   The basic morphology of
    plants reflects adaptations
    that have developed so that
    an organism can inhabit and
    obtain resources from soil
    and air.
   Two systems
       Subterranean root system
       Aerial root system
           Stems and leaves
       Neither system is
        independent of the other
Introduction II
   Most absorption occurs near the root tips
       Vast number of root hairs found
           Increase the surface area of the root
           Extensions of epidermal cells
               Previously covered
   Adventitious tissue is any tissue that grows in an atypical
    location
   Roots that develop out of above ground stems or leaves
    are called adventitious roots
       Provide additional support for taller plants.
Root System
   Roots are generally
    underground, obtains water
    and dissolved nutrient
    minerals for the plant and
    stores food.
   Anchors the plant firmly in
    place.
   Fibrous root systems
       Observed in seedless vascular
        plants and most monocots.
       Mats of thin roots that spread
        out through the soil
           Grasses and mangroves
Root System
   Taproot System
       Make up many eudicots and gymnosperms
       Consist of one large vertical root that produces many smaller
        lateral or branch roots
       Firmly anchors the plant in the soil
       Some store food (starch) that can be consumed by the plant
        when the plant is fruiting or flowering
           Most tree species
Modified Roots
Modified Roots I
   Prop Roots
       Develop from branches, or
        a vertical stem and grow
        downward into the soil to
        help support certain plants
        in an upright position
           Fichus tree South Florida?
   Buttress Roots
       Swollen bases or braces
        that support certain
        tropical rainforest trees
        that have shallow root
        systems
Modified Roots II
   Pneumatophores
       Aerial “breathing” roots
        that may assist in getting
        oxygen to submerged roots
   Contractile Roots
       Roots that grow into the
        soil and then contract
       Pulling plant deeper into
        the soil
           Corms
           bulbs
Mutualistic Relationship Between
       Roots & Other Organisms
Relationships
   Mycorrhizae
       Mutually beneficial associations between roots and soil fungi
   Root nodules
       Swellings that develop on roots of legumes and house millions
        of rhizobia (nitrogen fixing bacteria)
   Root Graft
       Natural connection between the roots of trees belonging to
        the same or different species.
Shoot System
Introduction I
   Shoots consist of stems and leaves
       Vegetative
           Leaf bearing
       Reproductive
           Flower bearing
Stems
   Stem
       Alternating system of
        nodes
           Locations where the leaves
            are attached
       Internodes
           Stem segments between
            nodes
       Auxiliary Bud
           Angle, or axil, formed by
            each leaf of the stem
           Has the potential to form a
            branch
               Most though are dormant
Stems II
   Growth of a young shoot is usually concentrated at its
    apex (tip), where there is a terminal bud with developing
    leaves and a compact series if nodes and internodes
   The presence of terminal bud prohibits the growth of the
    axillary bud
       Apical dominance
           “evolutionary response that directs growth toward light
Modified Stems
   Stolons/Runners
       Grow on the surface of the ground
       Increase surface area
       Can colonize asexually if plant is
        fragmented
           Strawberry
   Rhizomes
       Horizontal stems that grow
        underground
           Ginger
   Tubers
       Swollen ends of rhizomes specialized
        for storing food
           Potato
   Bulbs
       Vertical, underground shoots consisting
        mostly of swollen bases of leaves that
        store food
           onions
Leaves
   The main photosynthetic organ
   Consist of a flattened blade and a petiole
       Stalk
       Joins the leaf to the node on the stem
   Leaves are in various sizes, shapes and arrangement of
    leaves.
Differences Between Plant &
             Animal Growth
Differences Between Plant & Animal Growth
   Growth in plants, unlike animals, is localized in specific
    regions called meristems, and involves three processes
       Cell division
       Cell elongation
       Cell differentiation
   Plant growth is not limited to an embryonic period
   Most plants have indeterminate growth
Life Cycles
Life Cycles
   Annuals
       Complete their life cycle from germination to flowering and
        seed production and death in one year or less
           Wildflowers
   Biennials
       Live for two years
       There is a dormant period between vegetative growth and
        flowering
           Carrots
           Beets
   Perennials
       Long lived plants and include trees, shrubs and some grasses.
Indeterminate Growth
   Unrestricted growth in stems
    and growth
   This pattern of growth
    depends in the location of the
    meristems
       Meristems are regions of
        undifferentiated, embryonic
        cells. Initially, the cells are
        totipotent and can
        differentiate/mature into any
        other type of cell.
   Apical meristems
       Responsible for primary growth
       Located at the tips of roots,
        shoots and within the buds of
        stems
Indeterminate Growth
   Lateral meristems
       Cylinders of dividing cells
        that extend along the
        length of the roots and
        shoots provide for an
        increase in girth
       Responsible for secondary
        growth
           Vascular cambium
           Cork cambium
Primary vs. Secondary Growth
Primary Growth
   Increase in stem or root length
   Occurs in all plants
   Restricted to the youngest part of the plant.
Primary Growth
Fig 34.12                Fig 35.15
Primary Growth of Root   Primary Growth of Shoot
Secondary Growth
   Increase in stem or root girth
   Typically occurring in long cylinders of meristematic cells
    throughout the length of older stems and roots
   Occurs in all gymnosperms, most eudicots and rarely in
    monocots.
Secondary Growth II
Lateral Meristems
   Vascular cambium
       Produces secondary xylem (wood) and secondary phloem
           Secondary xylem
               Interior
           Secondary phloem
               Exterior
   Cork Cambium
       Produces thick, tough covering (cork cells) for stems and roots that
        replace the epidermis
   Recall what wood is composed of?
       Tracheids
       Vessel elements
       Fibers
      An overview of primary and secondary growth
                                                                              Primary growth in stems
             Shoot apical
             meristems
                                                                                                         Epidermis
             (in buds)
                                                                                                         Cortex
        In woody plants,
        there are lateral                                                                                Primary phloem
          meristems that
          add secondary                                                                                 Primary xylem
      growth, increasing                  Vascular
             the girth of                 cambium
                                                     Lateral
         roots and stems.                                                               Pith
                                                     meristems
                                          Cork
                                          cambium


      Apical meristems                                                       Secondary growth in stems
   add primary growth,                                                                              Periderm
   or growth in length.                                                                                   Cork
                                                                     Pith                                 cambium
                                                                                                               The cork
                                                                                                               cambium adds
                                                                                                               secondary
                                                                 Primary                                       dermal tissue.
                                                                 xylem                                      Cortex
                                                                                                             Primary
                                                                                                             phloem
                            Root apical                          Secondary                                     The vascular
                            meristems                            xylem                                         cambium adds
                                                                                                  Secondary
                                                                                                               secondary
                                                                                                  phloem
                                                                                 Vascular cambium              xylem and
                                                                                                               phloem.
Figure. 35.10

				
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