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Chapter 35: Plant Structure, Growth, and Development
Mrs. Valdes AP Biology
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Developmental Plasticity
DEFINE: ability to alter itself in response to its environment more marked in plants than animals environment more greatly affects phenotype than genetic make-up plant species by natural selection accumulate characteristics of morphology that vary little within the species TWO types of leaves
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Concept 35.1: The plant body has a hierarchy of organs, tissues, and cells
Plants have organs composed of different tissues, composed of cells Three basic organs: Roots Stems Leaves Basic morphology of vascular plants reflect evolution as organisms that draw nutrients from below ground and to be used above ground Organs organized into root system and shoot system Roots rely on sugar produced by photosynthesis in shoot system Shoots rely on water and minerals absorbed by root system
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Roots Roots: multicellular organs with important functions:
Anchor plant Absorb minerals and water Store organic nutrients Taproot system: consists of one main vertical root that gives rise to lateral roots, or branch roots Adventitious roots: arise from stems or leaves Seedless vascular plants and monocots: have fibrous root system characterized by thin lateral roots with no main root Most plants absorption of water and minerals occurs near root hairs, where vast numbers of tiny root hairs increase the surface area Prop Roots: Aid in support of tall, top-heavy plants; Storage Roots: store food & water in roots; “Strangling” aerial roots: seeds of strangler fig tree germinate in branches of other trees, then send lots of aerial roots around host tree until it is totally shaded out and dies; Buttress roots: Look like buttress and support large trunk; Pneumatophores: “air roots”; roots go above water to get oxygen since oxygen is poor in muddy mangrove waters
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Prop Roots: Aid in support of tall, top-heavy plants
Storage Roots: store food & water in roots; “Strangling” aerial roots: seeds of strangler fig tree germinate in branches of other trees, then send lots of aerial roots around host tree until it is totally shaded out and dies Buttress roots: Look like buttress and support large trunk Pneumatophores: “air roots”; roots go above water to get oxygen since oxygen is poor in muddy mangrove waters
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Stems Stem: organ consisting of :
alternating system of nodes, points at which leaves are attached Internodes: stem segments between nodes Axillary bud: structure that has potential to form a lateral shoot, or branch Apical bud: AKA terminal bud; located near shoot tip and causes elongation of young shoot Apical dominance: helps to maintain dormancy in most nonapical buds Rhizomes: horizontal shoot that grows just below surface
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Rhizomes: horizontal shoot that grows just below surface; vertical shoots arise from axillary buds on rhizome Bulbs: vertical underground shoots consisting of mostly enlarged bases of leaves that store food Stolons: horizontal shoots that grow along surface; “runners” enable plant to reproduce asexually Tubers: enlarged ends of rhizomes or stolons that specialize in storing food
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Leaves Leaf: main photosynthetic organ of most vascular plants
generally consist of flattened blade and stalk called the petiole, which joins leaf to node of stem Monocots and eudicots differ in arrangement of veins, vascular tissue of leaves Most monocots have parallel veins Most eudicots have branching veins In classifying angiosperms, taxonomists may use leaf morphology as criterion
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Tendrils: usually modified leaves but can be modified stems; “lassoed” support anchors plant and brings it closer to support Spines: modified leaves; photosynthesis carried out by fleshy green part of cacti Storage leaves: most succulents modified to store water Reproductive leaves: adventitious plantlets can fall off and take root in soil Bracts: NOT petals but modified leaves that surround a group of flowers
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Dermal, Vascular, and Ground Tissues
Each plant organ has dermal, vascular, and ground tissues Tissue system: functional unit connecting all plant’s organs Dermal tissue system: plants outer protective covering Cuticle: waxy coating helps prevent water loss from epidermis Periderm: in woody plants, protective tissues that replace epidermis in older regions of stems and roots Trichomes: outgrowths of shoot epidermis; can help with insect defense
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Stele: vascular tissue of stem or root
Vascular tissue system: carries out long-distance transport of materials between roots and shoots two vascular tissues : Xylem: conveys water and dissolved minerals upward from roots into the shoots Phloem: transports organic nutrients (FOOD) from where they are made to where they are needed Stele: vascular tissue of stem or root In angiosperms stele of root is a solid central vascular cylinder stele of stems and leaves divided into vascular bundles, strands of xylem and phloem
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Ground tissue system: tissues neither dermal nor vascular
includes cells specialized for storage, photosynthesis, and support Pith: ground tissue internal to vascular tissue Cortex: ground tissue external to vascular tissue
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Common Types of Plant Cells
Plant characterized by cellular differentiation, the specialization of cells in structure and function Plant cell types: Parenchyma Collenchyma Sclerenchyma Water-conducting cells of the xylem Sugar-conducting cells of the phloem
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Parenchyma Cells Mature parenchyma cells
Have thin and flexible primary walls Lack secondary walls Are least specialized Perform most metabolic functions Retain ability to divide and differentiate
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Collenchyma Cells Collenchyma cells: grouped in strands; help support young parts of plant shoot have thicker and uneven cell walls lack secondary walls provide flexible support without restraining growth
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Sclerenchyma Cells Sclerenchyma cells: rigid because of thick secondary walls strengthened with lignin dead at functional maturity Two types: Sclereids: short & irregular shape; thick lignified secondary walls Fibers: long and slender; arranged in threads
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Water Conducting Cells of Xylem
Two types of water- conducting cells: BOTH DEAD at maturity Tracheids: found in xylem of all vascular plants Vessel elements: common to most angiosperms and few gymnosperms align end to end to form long micropipes called vessels
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Sugar-Conducting Cells of Phloem
Sieve-tube elements: alive at functional maturity, though lack organelles Sieve plates: porous end walls that allow fluid to flow between cells along sieve tube Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells
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Concept 35.2: Meristems generate cells for new organs
Indeterminate growth: plant growth throughout its life Determinate growth: some plant organs cease to grow at a certain size Annuals: complete life cycle in a year or less Biennials: require two growing seasons Perennials: live for many years
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Lateral meristems: add thickness to woody plants, AKA secondary growth
Meristems: perpetually embryonic tissue; allow for indeterminate growth Apical meristems: located at tips of roots and shoots and at axillary buds of shoots elongate shoots and roots, AKA primary growth Lateral meristems: add thickness to woody plants, AKA secondary growth two lateral meristems: vascular cambium: adds layers of vascular tissue called secondary xylem (wood) and secondary phloem cork cambium: replaces epidermis with periderm, which is thicker and tougher
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Primary growth in stems
Fig Primary growth in stems Epidermis Cortex Shoot tip (shoot apical meristem and young leaves) Primary phloem Primary xylem Pith Lateral meristems: Vascular cambium Secondary growth in stems Cork cambium Axillary bud meristem Periderm Cork cambium Cortex Figure An overview of primary and secondary growth Pith Primary phloem Primary xylem Root apical meristems Secondary phloem Secondary xylem Vascular cambium
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Meristems give rise to:
initials: remain in meristem, derivatives: become specialized in developing tissues In woody plants, primary and secondary growth occur simultaneously but in different locations
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Concept 35.3: Primary growth lengthens roots and shoots
Primary plant body: produced by primary growth; parts of root and shoot systems produced by apical meristems Root cap: covers root tip; protects apical meristem as root pushes through soil Growth occurs just behind the root tip, in three zones of cells: Zone of cell division Zone of elongation Zone of maturation
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Primary growth of roots produces:
epidermis ground tissue vascular tissue In most roots, stele is vascular cylinder Ground tissue fills cortex (region between vascular cylinder and epidermis) Endodermis: innermost layer of the cortex is called the
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Lateral roots arise from within pericycle
Fig Lateral roots arise from within pericycle outermost cell layer in vascular cylinder 100 µm Epidermis Emerging lateral root Lateral root Cortex Figure The formation of a lateral root 1 Vascular cylinder 2 3
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Primary Growth of Shoots
Shoot apical meristem: dome- shaped mass of dividing cells at shoot tip Leaves develop from leaf primordia along sides of apical meristem Axillary buds develop from meristematic cells left at bases of leaf primordia
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Tissue Organization of Stems
Lateral shoots develop from axillary buds on stem’s surface In most eudicots, vascular tissue consists of vascular bundles arranged in ring In most monocot stems, the vascular bundles scattered throughout the ground tissue, rather than forming a ring
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Tissue Organization of Leaves
Epidermis in leaves interrupted by stomata, which allow CO2 exchange between air and photosynthetic cells in leaf Each stomatal pore is flanked by two guard cells, which regulate its opening and closing Mesophyll: ground tissue in a leaf; sandwiched between the upper and lower epidermis Spongy mesophyll: where gas exchange occurs; below palisade mesophyll in upper part of leaf vascular tissue of each leaf is continuous with vascular tissue of the stem Veins: leaf’s vascular bundles; function as leaf’s skeleton Each vein enclosed by protective bundle sheath
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Fig. 35-18 Figure 35.18 Leaf anatomy Guard cells Key to labels
Stomatal pore 50 µm Dermal Epidermal cell Ground Cuticle Sclerenchyma fibers Vascular Stoma (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Upper epidermis Palisade mesophyll Bundle- sheath cell Spongy mesophyll Figure Leaf anatomy Lower epidermis 100 µm Cuticle Xylem Phloem Vein Guard cells Vein Air spaces Guard cells (a) Cutaway drawing of leaf tissues (c) Cross section of a lilac (Syringa)) leaf (LM)
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(a) Cutaway drawing of leaf tissues
Fig a Key to labels Dermal Ground Cuticle Sclerenchyma fibers Vascular Stoma Upper epidermis Palisade mesophyll Figure Leaf anatomy Bundle- sheath cell Spongy mesophyll Lower epidermis Cuticle Xylem Phloem Vein Guard cells (a) Cutaway drawing of leaf tissues
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Surface view of a spiderwort (Tradescantia) leaf (LM)
Fig b Guard cells Stomatal pore 50 µm Epidermal cell Figure Leaf anatomy (b) Surface view of a spiderwort (Tradescantia) leaf (LM)
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Cross section of a lilac (Syringa) leaf (LM)
Fig c Upper epidermis Key to labels Palisade mesophyll Dermal Ground Vascular Spongy mesophyll Lower epidermis 100 µm Figure Leaf anatomy Vein Air spaces Guard cells (c) Cross section of a lilac (Syringa) leaf (LM)
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Concept 35.4: Secondary growth adds girth to stems and roots in woody plants
Secondary growth occurs in stems and roots of woody plants but rarely in leaves Secondary plant body: tissues produced by vascular cambium and cork cambium characteristic of gymnosperms and many eudicots, but NOT monocots
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Primary and secondary growth in a two-year-old stem Primary xylem
Fig a1 Pith (a) Primary and secondary growth in a two-year-old stem Primary xylem Vascular cambium Epidermis Primary phloem Cortex Cortex Primary phloem Epidermis Vascular cambium Primary xylem Pith Periderm (mainly cork cambia and cork) Figure Primary and secondary growth of a stem Secondary phloem Secondary xylem
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Primary and secondary growth in a two-year-old stem Primary xylem
Fig a2 Pith (a) Primary and secondary growth in a two-year-old stem Primary xylem Vascular cambium Epidermis Primary phloem Cortex Cortex Primary phloem Epidermis Vascular cambium Growth Vascular ray Primary xylem Secondary xylem Pith Secondary phloem First cork cambium Cork Periderm (mainly cork cambia and cork) Figure Primary and secondary growth of a stem Secondary phloem Secondary xylem
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Primary and secondary growth in a two-year-old stem Primary xylem
Fig a3 Pith (a) Primary and secondary growth in a two-year-old stem Primary xylem Vascular cambium Epidermis Primary phloem Cortex Cortex Primary phloem Epidermis Vascular cambium Growth Vascular ray Primary xylem Secondary xylem Pith Secondary phloem First cork cambium Cork Periderm (mainly cork cambia and cork) Most recent cork cambium Figure Primary and secondary growth of a stem Cork Secondary phloem Bark Layers of periderm Secondary xylem
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Cross section of a three-year- old Tilia (linden) stem (LM)
Fig b Secondary phloem Bark Vascular cambium Cork cambium Late wood Secondary xylem Periderm Early wood Cork 0.5 mm Figure Primary and secondary growth of a stem Vascular ray Growth ring (b) Cross section of a three-year- old Tilia (linden) stem (LM) 0.5 mm
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Vascular Cambium and Secondary Vascular Tissue
Vascular cambium: cylinder of meristematic cells one cell layer thick develops from undifferentiated parenchyma cells in cross section appears as a ring of initials initials increase vascular cambium’s circumference and add secondary xylem to inside and secondary phloem to outside
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Secondary xylem accumulates as wood, and consists of:
tracheids vessel elements (only in angiosperms) fibers Early wood: formed in spring, has thin cell walls to maximize water delivery Late wood: formed in late summer, has thick-walled cells and contributes more to stem support In temperate regions, vascular cambium of perennials dormant through winter Tree rings visible where late and early wood meet; can be used to estimate a tree’s age Dendrochronology: analysis of tree ring growth patterns; can be used to study past climate change What does this graph tell you? Graph of Mongolian conifers: More growth=farther rings = warmer climate; Warmest climate from
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As a tree or woody shrub ages, older layers of secondary xylem, AKA heartwood, no longer transport water and minerals Outer layers, known as sapwood, still transport materials through the xylem Older secondary phloem sloughs off and does not accumulate
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Cork Cambium and Production of Periderm
Cork cambium: gives rise to secondary plant body’s protective covering, or periderm Periderm consists of cork cambium plus layers of cork cells it produces Bark: consists of all tissues external to vascular cambium, including secondary phloem and periderm Lenticels: in periderm allow for gas exchange between living stem or root cells and outside air
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Concept 35.5: Growth, morphogenesis, and differentiation produce the plant body
Morphogenesis: development of body form and organization Three developmental processes act in concert to transform the fertilized egg into a plant: growth morphogenesis cellular differentiation
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Molecular Techniques Revolutionize the Study of Plants
Arabidopsis: model organism, and first plant to have its entire genome sequenced Studying genes and biochemical pathways of Arabidopsis provide insights into plant development
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Growth: Cell Division and Cell Expansion
By increasing cell number, cell division in meristems increases potential for growth Cell expansion accounts for actual increase in plant size Plane (direction) and symmetry of cell division are immensely important in determining plant form If planes of division parallel to plane of first division, single file of cells is produced If the planes of division vary randomly, asymmetrical cell division occurs
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Plane in which cell divides determined during late interphase
Microtubules become concentrated into ring called preprophase band that predicts future plane of cell division
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Orientation of Cell Expansion
Plant cells grow rapidly and “cheaply” by intake and storage of water in vacuoles AKA “Water Weight” Plant cells expand primarily along plant’s main axis Cellulose microfibrils in cell wall restrict direction of cell elongation
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Morphogenesis and Pattern Formation
Pattern formation: development of specific structures in specific locations controlled by homeotic genes determined by positional information in form of signals indicating to each cell its location may be provided by gradients of molecules Polarity: having structural or chemical differences at opposite ends of organism, provides one type of positional information Polarization initiated by asymmetrical first division of plant zygote In gnom mutant of Arabidopsis, establishment of polarity is defective
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Gene Expression and Control of Cellular Differentiation
Cellular differentiation depends on positional information and is affected by homeotic genes Positional information underlies all processes of development: growth, morphogenesis, and differentiation Cells NOT dedicated early to forming specific tissues and organs Cell’s final position determines what kind of cell it will become
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Shifts in Development: Phase Changes
Phase changes: developmental phases from juvenile phase to adult phase occur within shoot apical meristem Most obvious morphological changes typically occur in leaf size and shape
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Genetic Control of Flowering
Flower formation involves phase change from vegetative growth to reproductive growth Triggered by combination of environmental cues and internal signals Transition associated with switching on of floral meristem identity genes Plant biologists identified several organ identity genes (plant homeotic genes) that regulate development of floral pattern Mutation in plant organ identity gene abnormal floral development
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Researchers identified three classes of floral organ identity genes
ABC model of flower formation identifies how floral organ identity genes direct formation of four types of floral organs Understanding mutants of organ identity genes depict how this model accounts for floral phenotypes
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(a) A schematic diagram of the ABC hypothesis B C
Fig a Sepals Petals Stamens A Carpels (a) A schematic diagram of the ABC hypothesis B C C gene activity B + C gene activity Carpel A + B gene activity Petal Figure The ABC hypothesis for the functioning of organ identity genes in flower development A gene activity Stamen Sepal
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(b) Side view of flowers with organ identity mutations
Fig b Active genes: B B B B B B B B A A A A A A C C C C A A C C C C C C C C A A C C C C A A A B B A A B B A Whorls: Carpel Stamen Petal Figure The ABC hypothesis for the functioning of organ identity genes in flower development Sepal Wild type Mutant lacking A Mutant lacking B Mutant lacking C (b) Side view of flowers with organ identity mutations
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You should now be able to:
Compare the following structures or cells: Fibrous roots, taproots, root hairs, adventitious roots Dermal, vascular, and ground tissues Monocot leaves and eudicot leaves Parenchyma, collenchyma, sclerenchyma, water-conducting cells of the xylem, and sugar-conducting cells of the phloem Sieve-tube element and companion cell Explain the phenomenon of apical dominance Distinguish between determinate and indeterminate growth Describe in detail the primary and secondary growth of the tissues of roots and shoots Describe the composition of wood and bark Distinguish between morphogenesis, differentiation, and growth Explain how a vegetative shoot tip changes into a floral meristem
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Explain the phenomenon of apical dominance
Distinguish between determinate and indeterminate growth Describe in detail the primary and secondary growth of the tissues of roots and shoots Describe the composition of wood and bark
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Distinguish between morphogenesis, differentiation, and growth
Explain how a vegetative shoot tip changes into a floral meristem
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