Download Ch. 35 Plant Structure, Growth, and Development

Ch. 35
Plant Structure, Growth, and Development
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Essential Question:
How is the structure of the plant related to its function?
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Tissue = a group of cells with a common function, structure or both
Organ = several types of tissues that carry out a particular function
Three basic plant organs = roots, stems and leaves
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The Body of a Plant
A. Root system
root = organ that anchors a vascular plant, absorbs minerals and water, and can store organic nutrients
Two types of roots
1. taproot system ­ one vertical root that develops from embryonic root
­lateral roots (branch roots) come off of taproot
­found in eudicots (many flowering plants that have two cotyledons)and gymnosperms
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tap roots ­go deep into ground
Ex. carrots, turnips, sugar beets
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2. Fibrous root system ­ a mat of thin roots that spread just below soil surface, with no main root
­found in seedless vascular plants and most monocots (ex. grasses)
embryonic root dies, roots grow from stem
each root has lateral roots
these roots are adventitious ­ a part of a plant that grows in an unusual location
prevent soil erosion
http://www.botany.uwc.ac.za/ecotree/root/roottypes.htm
root hair­ extension of a root epidermal cell ­ increase surface area
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Other modified roots:
• prop roots ­ aerial roots, Ex corn
storage roots ­ store food Ex. beets
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• strangling aerial roots ­ plants that germinate in branches of tall trees and send aerial roots to ground
• buttress roots ­ aerial roots that look like buttresses
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• pneumatophores ­ air roots Ex. mangroves
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B. stem = an organ made of an alternating system of nodes (points where leaves attach) and internodes (segment in between nodes)
axillary bud­ found in the angle formed by stem and leaf
a structure that has the of potential of forming a lateral shoot most are dormant
terminal bud (apical bud)­ young shoot located near shoot apex
­has compact nodes and internodes
apical dominance­ when a plant puts its resources to elongating the plant
­increases ability to get light
if terminal bud can't work, axillary buds will then come out of dormancy ­ result = more lateral shoots
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Axillary and terminal buds
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Modified stems:
Rhizomes ­ horizontal shoot that grows just below surface of ground
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Bulbs: ­ vertical underground shoots consisting of the enlarged bases of leaves that store food
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Stolons: ­ horizontal shoots that grow along the surface of ground ­ "runners"
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tubers ­ enlarged ends of rhizomes or stolons specialized for storing food
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C. Leaves­ photosynthetic organ of plant (stems can also do photosynthesis)
blade
components:
blade ­flattened part of leaf
petiole­ joins leaf to node of stem
some plants lack this (ex. grasses)
veins­ vascular tissue of leaf
monocots have parallel veins, length of blade
eudicots ­ multibranched with a network of veins
veins
petiole
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can classify by shape
simple ­ single undivided ,vein
compound­ blade has many leaflets
double compound­ each leaflet is divided
into smaller leaflets
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Leaf modifications
tendrils­ fasten plant, support (peas)
spines­ to conserve water (cactus), protection
storage leaves­ hold water (succulents)
Bracts ­ leaves that surround a flower
red leaves of poinsettia, attract pollinators
reproductive leaves­ make plantlets
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leaves, stems and roots are made of three tissue systems
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a. dermal tissue system­ outer protective layer
­first line of defense
­called epidermis in non woody plants ­ tightly packed cells
­called periderm in woody plants­ replace older regions of roots and stems
­some have cuticle to prevent water loss ­ waxy coating
b. Vascular tissue system­ long­distance transport of materials between roots and shoots
xylem, phloem
stele­ vascular tissue of a root or stem
arrangement of stele depends on species and organ
­ angiosperms ­ root has vascular cylinder, stems and leaves have vascular bundles (both xylem and phloem)
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xylem
phloem
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c. Ground tissue system­tissue that isn't dermal or vascular
pith­ground tissue that is internal to vascular tissue in stem cortex­ ground tissue external to vascular tissue
functions: storage, photosynthesis and support
http://www.backyardnature.net/woodtwi2.htm
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Types of plant cells
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1. parenchyma ­ primary wall ­ thin, flexible
­lack secondary wall
­large vacuole when mature
­typical plant cell
­ function ­ perform most metabolic functions of plant
­phototsynthesis, storage of starch
­ can divide
2. Collenchyma
­ function: help support young parts of plant shoot
­thicker primary walls
­lack secondary wall
­ex strings in celery stalk
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3. Sclerenchyma
­support plants, rigid
­have secondary walls ­ thick (lignin)
­in part of plant not growing
two types:
a. sclerids ­ short, irregular shape,
give hardness to nut shells, gritty texture of pears
support and strengthening
b. fibers ­ long, slender, tapered threads
ex: hemp fibers for rope
flax fibers for linen
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4. Water conducting cells
­dead at maturity
a. tracheids
­found in xylem of all vascular plants
­dead, tubular, long cells
­water moves cell to cell through pits
b. vessel elements ­ wider, shorter,
thinner walled cells
­attached end to end, making long pipes
­end walls have perforations to let water flow freely
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5. Sugar conducting cells of phloem
­alive at maturity, but lack organelles
­sieve cells ­long narrow cells that transport sugar
­sieve tube members ­ chains of sieve cells
­sieve plates ­ end walls between sieve tube members
­have pores
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­companion cells ­ plant cell that is connected to a sieve tube member by many plasmodesmata and whose nucleus and ribosomes may serve one or more adjacent sieve tube members
­ some plants these are loading areas into the sieve tube members
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Growth of plants
indeterminate growth ­ growth occurring throughout live of plant
determinate growth ­ stop growing after reaching certain size
Ex. leaves, thorns and flowers
Length of life cycle:
Annuals ­ complete life cycle in single year Ex. legumes, grains
Biennials ­ require two growing seasons to complete life cycle
Ex. radishes, carrots
Perennials ­ live many years Ex. trees, shrubs, some grasses
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Indeterminate growth
­plant has embryonic, developing and mature at same time
­can do this due to meristems ­ embryonic tissue
­initials = "stem cells" of plant
­derivatives = specialized cells
a. apical meristems­ tips of roots, buds of shoots
­have primary growth ­ growing in length
­ in herbaceous plants (non woody) ­ makes all of plant body ­ in woody plants ­ secondary growth caused by lateral meristems (growth in thickness)
b. lateral meristems (vascular cambium and cork cambium)
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­vascular cambium ­ adds layers of vascular tissue called secondary xylem (wood) and secondary phloem
­cork cambium = replaces epidermis with periderm
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Three years' growth
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How do roots grow?
root cap­ protects meristem
pushed through soil
secretes polysaccharide (lubrication)
zone of cell division ­ primary meristems
quiescent center ­ area of slow growth in apical meristem
protoderm ­ will become dermal layer
procambium­ will become vascular layer
ground meristem ­ will become ground tissue layer
zone of elongation ­ cells elongate
zone of maturation (zone of differentiation)­cells become mature and distinct cell types
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root structure
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Root with xylem and phloem in center ­ (typical of eudicots)
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xylem and phloem of eudicot in root
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Root with parenchyma in the center( typical of monocots)
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Lateral roots grow from pericycle ­ outermost layer in vascular cylinder, pushes through cortex and epidermis
­grows from center because its vascular system must be continuous with center vascular cylinder
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How do shoots grow?
­shoot apical meristem ­ dome­shaped mass of dividing cells at shoot tip
­ in a bud ­ leaves form from leaf primordia on sides of apical meristem
­shoot elongation is due to internodes that lengthen
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The shoot tip
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Vascular bundles
Organization of primary tissues in young stems
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Review of leaf anatomy
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Stomata ­ pores for gas exchange
­regulate CO2 uptake for photosynthesis
­regulate water loss
­flanked by two guard cells ­ regulate opening of stomata
mesophyll­ parenchyma cells for photosynthesis
palasade mesophyll
spongy mesophyll
Veins = leaf's vaxcular bundles
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Primary growth ­ occurs in apical meristems and involves production and elongation of roots, stems and leaves
Secondary growth ­ growth in diameter
­produced by vascular cambium and cork cambium
­happens in all gymnosperms, in dicot angiosperms
­not in monocot angiosperms
­thickens stems and roots
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Vascular cambium ­ function to add secondary xylem to inside of cambium and secondary phloem to outside of cambium
Cork cambium produces cork
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Secondary growth of a stem
1. primary growth forms vascular cambium
2. secondary xylem and phloem form 3. initials give rise to vascular rays
4. cork cambium forms cork
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Production of secondary xylem and phloem
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stems­ due to vascular cambium and secondary vascular tissue made
ray initials ­ cambium cells that produce radial parenchyma cells
fusiform initials ­ make new vascular tissue (secondary)
periderm = cork + cork cambium
bark­ all tissues external to the vascular cambium
(phloem + periderm)
can look at tree rings for secondary growth
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Dendrochronology = study of tree ring growth
­rings vary in thickness depending on seasonal growth
Three year old stem
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heartwood = older layers of secondary xylem that no longer transport water and minerals
sapwood = newest, outer layers of xylem that transport sap
lenticels = small, raised areas of periderm; space between cork cells so living cells can live ­ some gas exchange
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Wawona Sequioa in Yosemite national Park
­ cut in 1881
­ lived another 88 years
*tree do not need heartwood to survive
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Plant growth, morphogenesis and differentiation
Plant growth ­ involves cell division and expansion
plane and symmetry of cell division can influence form
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asymmetrical cell division ­ where one daughter cell receives more cytoplasm than other cell
ex. to make guard cells
­plane of cell division is laid down in late interphase
­ is called the preprophase band
­disappears before metaphase
cell expansion adds length of cells ­ usually due to extra water
­grows in plane perpendicular to microfibrils
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plane of symmetry
preprophase band and plane of cell division
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Orientation of plant cell expansion
­usually due to water uptake
­cell enzymes weaken cross­links of cell wall which allow it to expand
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morphogenesis­ organization into tissues and organs
called pattern formation
­depends on positional information ­ signals in embryonic tissue
A. wild­type
B. fass mutant seedling
­ex. polarity ­ root and shoot ends
C. Mature fass mutant
happens in first division of zygote
A.
genes are important
B.
C.
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differentiation
­occurs throughout plant's life
­depends on genes expression too
phase changes ­
a. vegetative growth from juvenile state to mature state
ex. change in leaf structure
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regular expression of gene
over expression of gene
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b. vegetative shoot tip to floral meristem
triggers: day length, hormones
­meristem identity genes get turned on to make floral meristem
­organ identity genes also promote change to a particular organ ex. stamen
phase change in shoot system of Eucalyptus
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ABC model of flower formation
identifies how three classes of genes direct the formation of four types of floral organs
each class of organ identity genes is switched on in two specific whorls of the floral meristem
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What would happen if had mutant lacking A and B?
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So, How is the structure of the plant related to its function?
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