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SC.912.L.14.7Plant Structures and Functions
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Plant Structures and Functions
1. Monocots vs. Dicots Root structure and vasculature Stem vasculature Leaf structure and vasculature 2. Plant tissues Dermal (epidermis) Vascular Ground Meristematic 3. Plant organs Roots Stems Leaves Flowers and Cones 4. Plant Growth Meristems – apical, axillary, lateral Vascular cambium vs. cork cambium
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Plant Classification – Monocots vs. Dicots
Basic categories of plants based on structure and function
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Three Basic Plant Organs: Roots, Stems, and Leaves
Plant “bodies” Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells Shoot system Leaf Stem Three Basic Plant Organs: Roots, Stems, and Leaves Root system
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Plant Tissues Dermal tissue Ground Vascular Each plant organ has dermal, vascular, and ground tissues Each of these three categories forms a tissue system
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Plant Tissues 1) Dermal Tissue System Outer covering Protection
2) Vascular Tissue System “Vessels” throughout plant Transport materials 3) Ground Tissue System “Body” of plant Photosynthesis; storage; support
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Plant Tissues - Dermis Dermal Tissue System (Outer Covering of Plant):
1) Epidermal Tissue (epidermis): Forms outermost layer Cuticle: Waxy covering Reduces evaporation Inhibits microorganism invasion Root Hairs: extended root surface Increase absorption 2) Peridermal Tissue (periderm): Only in woody plants (“bark = dead cells”) Protection; support
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Plant Tissues - Dermis Special Dermal Cells – Guard Cells
Stomata Stomata Guard cells Guard cells Epidermal cell Epidermal cell a. c. 4 µm 200 µm Paired sausage-shaped cells Flank a stoma – epidermal opening Passageway for oxygen, carbon dioxide, and water vapor Stoma Stoma Epidermal cell Epidermal cell Guard cells Guard cells b. 71 µm
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Plant Tissues - Dermis Special Dermal Cells – Trichomes & Root hairs
Hairlike outgrowths of epidermis Keep leaf surfaces cool and reduce evaporation Roots hairs Tube extensions from epidermal cells Greatly increase the root’s surface area for absorption
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Plant Tissues - Vascular
1) Xylem (dead at maturity): Tracheids: Narrow, tube-like cells Vessel Elements: Wide, tube-like cells
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Plant Tissues - Vascular
Vascular Transport System 1) Xylem (dead at maturity): - Moves water & minerals from roots to shoots
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Plant Tissues - Vascular
Sieve Tubes: Wide, tube-like cells B) Companion Cells: support and regulate sieve tubes 2) Phloem (living at maturity)
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Plant Tissues - Vascular
Vascular Transport System 2) Phloem (living at maturity) - Moves water, sugar, amino acids & hormones
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Vasculature - Comparisons
Monocots and dicots differ in the arrangement of vessels in the roots and stems Dicots Monocots Stem Root
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Plant Tissues – Ground Tissue
Some major types of plant cells: Parenchyma Collenchyma Sclerenchyma Tissues that are neither dermal nor vascular are ground tissue Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex Ground tissue includes cells specialized for storage, photosynthesis, and support
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Plant Tissues - Ground Ground Tissue System (“Body” of Plant):
1) Parenchyma (most abundant): Thin-walled cells; living plant metabolism: Photosynthesis; hormone secretion; sugar storage FIGURE 42-5 The structure of ground tissue (a) Parenchyma cells are living and serve many functions. They have thin, flexible primary cell walls. These parenchyma cells are used for starch storage in a potato. (b) Collenchyma cells are living and have thickened, but somewhat flexible, primary walls. They help support the plant body (as seen in this celery stalk). (c) Sclerenchyma cells have thick, rigid secondary cell walls and die after they differentiate. Illustrated are "stone cells" that give pear fruit its slightly gritty texture. Parenchyma cells in Elodea leaf,(w/chloroplasts)
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Plant Tissues - Ground Ground Tissue System (“Body” of Plant):
2) Collenchyma: Thick-walled (uneven); living Offers support (flexible & strong) FIGURE 42-5 The structure of ground tissue (a) Parenchyma cells are living and serve many functions. They have thin, flexible primary cell walls. These parenchyma cells are used for starch storage in a potato. (b) Collenchyma cells are living and have thickened, but somewhat flexible, primary walls. They help support the plant body (as seen in this celery stalk). (c) Sclerenchyma cells have thick, rigid secondary cell walls and die after they differentiate. Illustrated are "stone cells" that give pear fruit its slightly gritty texture. Collenchyma cells sunflower
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Plant Tissues - Ground Ground Tissue System (“Body” of Plant):
Sclereid cells in pear (LM) Fiber cells in ash tree Cell wall 3) Sclerenchyma: Thick, hard-walled; Dead Offer support (e.g. hemp fibers; nut shells) FIGURE 42-5 The structure of ground tissue (a) Parenchyma cells are living and serve many functions. They have thin, flexible primary cell walls. These parenchyma cells are used for starch storage in a potato. (b) Collenchyma cells are living and have thickened, but somewhat flexible, primary walls. They help support the plant body (as seen in this celery stalk). (c) Sclerenchyma cells have thick, rigid secondary cell walls and die after they differentiate. Illustrated are "stone cells" that give pear fruit its slightly gritty texture.
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Roots - Overview Roots need sugars from photosynthesis;
Shoots rely on water and minerals absorbed by the root system Root Roles: - Anchoring the plant - Absorbing minerals and water - Storing organic nutrients
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Roots - Comparisons Taproots: Fibrous roots:
Typical of dicots, primary root forms and small branch roots grow from it In monocots mostly, primary root dies, replaced by new roots from stem
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Roots – Structure and Development
Four regions: Root cap Protection, gravity detection Zone of cell division Mitotic divisions Zone of elongation Cells lengthen, no division Zone of maturation Cells differentiate, outer layer becomes dermis
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Roots – Structure and Development
In maturation zone, Casparian strip forms – waterproof barrier material surrounding vasculature
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Roots – Structure and Development
Epidermis Primary phloem Primary xylem Pith Monocot Eudicot Endodermis Cortex Pericycle 48 µm 385 µm 8 µm Location of Casparian strip
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Roots – Many Plants Have Modified Roots
Prop roots “Strangling” aerial roots Storage roots Buttress roots Pneumatophores Roots – Many Plants Have Modified Roots Figure 35.4 Modified roots Water storage
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Stems - Overview Stem: an organ made of
Apical bud Node Internode Apical bud Shoot system Vegetative shoot Axillary Stem Stem: an organ made of An alternating system of nodes, points at which leaves attach Internodes, stem length between nodes Axillary bud - structure that can form a lateral shoot, or branch Apical/terminal bud - located near the shoot tip, lengthens a shoot Apical dominance maintains dormancy in most nonapical buds
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Stems – Structure and Development
Stems have all three types of plant tissue Grow by division at meristems Develop into leaves, other shoots, and even flowers Leaves may be arranged in one of three ways
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Stems - Comparisons Eudicot Monocot
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Stems – Many Plants Have Modified Stems
Rhizomes Bulbs Storage leaves Stem Stolons Stolon Tubers Figure 35.5 Modified stems
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Leaves - Overview Shoot system Leaf Blade Petiole The leaf is the main photosynthetic organ of most vascular plants Leaves generally have a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem
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Leaves – Structure and Development
Leaves are several layers thick – each with different cell types
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Leaves – Structure and Development
Most dicots have 2 types of mesophyll Palisade mesophyll high photosynthesis Spongy mesophyll air spaces for gas & water exchange Monocot leaves have 1 type of mesophyll
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Leaves - Comparisons Monocots and dicots differ in the arrangement of veins, the vascular tissue of leaves Most dicots have branch-like veins and palmate leaf shape Monocots have parallel leaf veins and longer, slender blades
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Leaves – Plants have modified leaves for various functions
Tendrils Spines Storage leaves Figure 35.7 Modified leaves Reproductive leaves Bracts
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Plant Growth Plant Growth: 1) Indeterminate: Grow throughout life
2) Growth at “tips” (length) and at “hips” (girth) Growth patterns in plant: 1) Meristem Cells: Dividing Cells 2) Differentiated Cells: Cells specialized in structure & role Form stable, permanent part of plant
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Plant Growth 1) Primary Growth: Apical Meristems:
girth length 1) Primary Growth: Apical Meristems: Mitotic cells at “tips” of roots / stems 1) Increased length 2) Specialized structures (e.g. fruits) 2) Secondary Growth: Lateral Meristems: Mitotic cells “hips” of plant Responsible for increases in stem/root diameter
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Plant Growth Shoot apical meristem Leaf primordia Young leaf
Developing vascular strand Figure The shoot tip Axillary bud meristems
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Plant Growth Two lateral meristems: vascular cambium and cork cambium
Shoot tip (shoot apical meristem and young leaves) Lateral meristems: Axillary bud meristem Vascular cambium Cork cambium Root apical meristems Primary growth in stems Epidermis Cortex Primary phloem Primary xylem Pith Secondary growth in stems Periderm Cork cambium Primary phloem Secondary xylem Figure An overview of primary and secondary growth
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Plant Growth Stem – Secondary Growth: thicker, stronger stems
primary phloem thicker, stronger stems Vascular Cambium: between primary xylem and phloem vascular cambium primary xylem epidermis Produces inside stem: pith A) Secondary xylem moves H2O, inward B) Secondary phloem moves sugars, outward cortex primary xylem dividing vascular cambium primary phloem
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Plant Growth Vascular Cambium: Secondary growth primary phloem
dividing vascular cambium new secondary xylem secondary phloem primary phloem vascular cambium primary xylem secondary xylem pith cortex Secondary growth Vascular cambium Growth Secondary xylem After one year of growth After two years phloem Vascular cambium X P C
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Plant Growth Stem – Secondary Growth: Cork Cambium:
ring Vascular ray Secondary xylem Heartwood Sapwood Bark Vascular cambium Secondary phloem Layers of periderm Located under outer surface; produces periderm Dead at maturity Protection
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Plant Growth Stem – Secondary Growth: heartwood (xylem) sapwood
vascular cambium phloem annual ring Sapwood = Young xylem, water Heartwood = Old xylem, support Seasonal Growth = annual rings Secondary phloem = grows outward older phloem crushed late xylem early xylem
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Plant Growth RESULTS 2 1.5 Ring-width indexes 1 0.5 1600 1700 1800
Figure 35.21 1600 1700 1800 1900 2000 Year Using dendrochronology to study climate
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Plant Growth Living tree or dead tree?
Figure Is this tree living or dead?
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Plant Growth - Roots Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem Phloem 100 µm Root with xylem and phloem in the center (typical of eudicots) (a) Root with parenchyma in the center (typical of monocots) (b) Key to labels Dermal Ground Figure Organization of primary tissues in young roots
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Plant Growth - Stems In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring Phloem Xylem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Cortex 1 mm Epidermis Vascular bundle Cross section of stem with vascular bundles forming a ring (typical of eudicots) (a) Key to labels Dermal Ground Cross section of stem with scattered vascular bundles (typical of monocots) (b) bundles tissue Figure Organization of primary tissues in young stems
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Plant Growth - Leaves Leaf epidermis contains stomata - allow CO2 exchange Stomata flanked by two guard cells, control open vs. closed The ground tissue in a leaf, called mesophyll, fills the middle Key to labels Dermal Ground Vascular Cuticle Sclerenchyma fibers Stoma Bundle- sheath cell Xylem Phloem (a) Cutaway drawing of leaf tissues Guard cells Vein Lower epidermis Spongy mesophyll Palisade Upper Stomatal pore Surface view of a spiderwort (Tradescantia) leaf (LM) Epidermal (b) 50 µm 100 µm Air spaces Guard cells Cross section of a lilac (Syringa)) leaf (LM) (c) Figure Organization of primary tissues in young stems
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Plant Structures and Functions Summary
1. Monocots vs. Dicots Root structure and vasculature Stem vasculature Leaf structure and vasculature 2. Plant tissues Dermal (epidermis) Vascular Ground 3. Plant organs Roots Stems Leaves 4. Plant Growth Meristems – apical, axillary, lateral Vascular cambium vs. cork cambium
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