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Plant Structure, Growth & Development
Packet #35 Chapters #35 & #38
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The Plant Body
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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
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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).
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Roots, Stems & Leaves
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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
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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.
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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
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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
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Modified Roots
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Modified Roots I Prop Roots Buttress 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
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Modified Roots II Pneumatophores Contractile Roots
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
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Mutualistic Relationship Between Roots & Other Organisms
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Relationships Mycorrhizae Root nodules Root Graft
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.
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Shoot System
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Introduction I Shoots consist of stems and leaves Vegetative
Leaf bearing Reproductive Flower bearing
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Stems Stem Alternating system of nodes Internodes Auxiliary Bud
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
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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
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Modified Stems Stolons/Runners Rhizomes Tubers Bulbs
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
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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.
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Differences Between Plant & Animal Growth
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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
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Life Cycles
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Life Cycles Annuals Biennials Perennials
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.
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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
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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
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Primary vs. Secondary Growth
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Primary Growth Increase in stem or root length Occurs in all plants
Restricted to the youngest part of the plant.
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Primary Growth Fig 34.12 Fig 35.15 Primary Growth of Root
Primary Growth of Shoot
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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.
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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
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Primary growth in stems Secondary growth in stems
An overview of primary and secondary growth Figure In woody plants, there are lateral meristems that add secondary growth, increasing the girth of roots and stems. Apical meristems add primary growth, or growth in length. Vascular cambium Cork Lateral meristems Root apical Primary growth in stems Epidermis Cortex Primary phloem Primary xylem Pith Secondary growth in stems Periderm Primary phloem Secondary Vascular cambium xylem Shoot apical (in buds) The cork cambium adds secondary dermal tissue. The vascular xylem and phloem.
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