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Plant structure, growth, & development ~ 35
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1. Plants have a hierarchical organization consisting of organs,
tissues, and cells• 3 basic organs
– Roots, stems, leaves• Shoot System
– Stems• Raises or separates leaves to expose to sunlight
– Leaves • Main photosynthetic organ
• Root System– Anchors a vascular plant in the soil– Absorbs minerals & H2O– Stores carbohydrates
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Dermal, Vascular, and Ground tissues = Tissue System
• Tissue system connects all of the plants organs• Dermal Tissue System– Epidermis, cuticle, periderm– Outer protective covering
• Vascular Tissue System– Xylem, phloem, stele– Long distance transport of materials btwn root & shoot systems
• Ground Tissue System– Pith, cortex– Specialized cells for storage, photosynthesis and support
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Differentiated Cell Types
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Differentiated Plant Cells
• Parenchyma Cells– Typical plant cell w/ lg central vac– Metabolic functions, synthesizing, & storing
organic products
• Collenchyma cells– Flexible Support & strength w/o restraining
growth (young parts of plant shoot), grouped in strands
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• Sclerenchyma Cells– Support & hardness– Much more rigid than Collenchyma lignin in cell
walls• Water Conducting cells of xylem– Support; harden as die at maturity– Hardening of tracheids & vessel elements tubes
to transport water; migrate btwn cells thru pits• Sugar Conducting cells of Phloem– Transport sugars throughout; alive at maturity– Chains of cells = sieve-tube elements & sieve
plates facilitate flow of sugars throughout plant
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2. Meristems generate cells for primary & secondary growth
• Intermediate Growth– Growth occurs throughout
life of plant– Meristems
• Apical– Primary Growth– Roots to extend in soil– Shoots expose to sunlight– Tips of roots, buds & shoots
• Lateral– Secondary Growth– Growth in thickness– Vascular cambium, Cork
cambium
• Determinate Growth– Leaves, thorns, flowers stop
growing after reach certain size
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3. Primary Growth Lengthens Roots & Shoots
• Primary growth of roots• Growth occurs behind root
cap in three overlapping zones
1. Cell Division2. Elongation3. Differentiation/Maturation
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• Primary growth of shoots• Apical meristem– Dome shaped mass of dividing cells
at the shoot tip– Shoot elongation due to
lengthening of cells below shoot tip
• Leaf primordia– Development of leaves
• Tissue Organization of Stems
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• Tissue Organization of Leaves– Epidermis
• Upper & lower• Pores = stomata• Gas exchange• Prevent loss of water• Guard cells regulate
opening/closing of stomata– Mesophyll
• Ground tissue (middle tissue)• Layers of parenchyma cells
– Vascular Tissue• Xylem & phloem reinforcing
shape of leaf = Vein• Bundle sheath cells protect
Vein
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4. Secondary Growth Increases the Diameter of Stems and Roots in Woody
Plants• Secondary growth (thickness produced from
lateral meristems) occurs in stems and roots of woody plants, rarely in leaves
• Tissues produced by vascular cambium & cork cambium– V.Cambium adds secondary xylem (= wood) and
phloem• Inc vascular flow and support for shoots
– C.Cambium tough, thick covering of wax protect the stem from water loss, insects, bacteria, fungi
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• Growth rings– Layers of sec. xylem accum– Tracheids, vessels, fibers– Walls of sec xylem heavily lignified= hardness & strength of wood
• Gymnosperms– Tracheids only
• Angiosperms– Tracheids & vessel elements
• Temperate regions– Early wood (spring; lrg cells) & late wood (summer; sml cells)– V.Cambium inactive in winter– Forms seasonal rings
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5. Growth, Morphogenesis, and Cell Differentiation Produce the Plant Body• Growth – inc in size by cell division• Morphogenesis = creation of plant shape– Tissue, organ, organism its shape & position of cell
types– Development of specific patterns = Pattern Formation
• Cell fate– Lineage-based determined early in development– Position-based cell’s final position in an emerging organ
determines what kind of cell it will become
• Differentiation = cells with same genes become different from one another – Gene expression; Hox genes in animals = MADS-box in
plants for transcription factors
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Organ identity genes
• Meristem identity genes– Vegetative growth flowering (floral meristems)
• Organ identity genes– Regulate development of floral pattern
• ABC Hypothesis– 3 classes of genes direct the formation of 4 types of
floral organs via gene activation for expression• A sepals & petals• B petals & stamens• C stamens & carpels