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Plant Structure and Growth
Chapter 35
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I) Plant Body A) controlled by 1) genes: they determine what structures will form 2) Environment: can alter gene expression depending on what is needed
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B) Basic Organs 1) Roots: * anchor * absorb minerals and water
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a) fibrous roots: a1) found on monocots a2) spread out right under soil * good coverage for absorption * helps hold soil in place
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b) Tapoot: Found on most dicots b1) long with branches for absorption b2) good anchor b3) stores food
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c) adventitious roots c1) roots that come from leaves or stem
c) adventitious roots c1) roots that come from leaves or stem * help support plant
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2) The shoot system: stems and leaves
a) Stem: a1) supports leaves at nodes * axillary bud: site on node where a branch can form
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a2) terminal bud: top of stem where growth for height occurs
a2) terminal bud: top of stem where growth for height occurs * this inhibits growth at axillary buds(apical dominance). If removed more branches will form
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b) leaves: main site of photosynthesis b1) blade = leaf b2) petiole: attaches blade to stem
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b3) monocot leaves: veins run parallel b4) dicot leaves: veins are branched
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C) Plant Tissues: dermal, vascular, and ground
1) dermal(epidermis): layer of cells that protects the plant a) cells will have different structure depending on what it is covering a1) ex: cuticle/waxy covering
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2) Vascular tissue: transports material through plant a) xylem: carry water and minerals a1) tracheids * long, tapered, with pits for water transfer
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a2) vessel elements: short, wide, perforated ends
a2) vessel elements: short, wide, perforated ends * water flows directly from one to another * string together to form vessels
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b) Phloem: carry sugar and minerals b1) cells called sieve-tube members(stm’s) * holes at end of tubes form sieve plate * alive, but don’t have nucleus, ribosomes, etc.
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b2) companion cell: live attached to stm’s
b2) companion cell: live attached to stm’s * connected to stm’s by plasmodesmata (specialized openings between cells) * provide proteins to stm’s
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3) Ground tissue a)all other tissue not vascular or epidermal a1) dicot stem: pith is inside of the vascular tissue, cortex is outside of it.
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D) Tissues made up of three cell types
1) Parenchyma: Have thin, flexible primary walls, no secondary walls. a) do most metabolism of the plant a1) photosynthesis, starch storage
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2) Collenchyma: thicker primary walls, they help support young parts of the plant. a) continue to elongate as the plant grows.
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3) Sclerenchyma: Thick primary and secondary walls
3) Sclerenchyma: Thick primary and secondary walls. Secondary wall has lignin for extra strength.
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a) dead at maturity, but formed as a helix so they stretch as the plant grows
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II) Plant Growth * annuals: complete life cycle in one year then die * biennial: two years * perennial: grows year after year, completing many flowering cycles
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A) Meristems 1) embryonic tissue where growth can occur
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a) apical meristem a1) tips of buds and roots for elongation
a) apical meristem a1) tips of buds and roots for elongation * elongation is called primary growth
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b) lateral meristem: tissue inside the stems and roots of a woody plant that makes the plant thicker. b1) vascular cambium adds xylem and phloem b2) cork cambium adds cork
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B) Root Growth 1) root cap a) protects root as it pushes through soil a1) secretes a polysaccharide that helps it slide through the soil
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2) Zone of Cell Division a1) high concentration of mitotically dividing cells a2) quiescent center – resistant to damage to replace apical meristem if damaged
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a3) procambium forms vascular tissue a4) protoderm turns into dermis a5) ground meristem forms ground tissue
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3) Zone of Elongation a) cells elongate to push the root down through the soil
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4) Zone of maturation a) area of final differnetiation
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5) Stele – tube of xylem and phloem running through center of root a) pericycle: outermost cells that can create a lateral root
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6) cortex: starch storage
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7) Endodermis: ring of cells between the stele and the cortex a) casparian strip: ring of fat around each cell that forces water through the cells to the stele so water cant leak back to the cortex
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C) Stems 1) vascular bundles: groupings of xylem and phloem that run the length of the stem.
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D) Leaves 1) Stomata: opening in the leaf for gas exchange 2) opening is controlled by guard cells
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3) mesophyll a) all tissue in between upper and lower epidermis
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b) palisade payer: main layer of photosynthesis c) spongy mesophyll: cells surrounding veins inleaf and stomata. Have air spaces between them.
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III) Secondary growth A) Stems 1) Vascular cambium a) produce xylem and phloem in woody plants a1) phloem to the outside, xylem to the inside
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a2) annual rings. xylem grows larger in spring/summer than fall/winter
a2) annual rings * xylem grows larger in spring/summer than fall/winter *Vascular growth animation
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2) Cork cambium a) replaces/thickens epidermis a1) outermost layer is cork, with suberin added a2) inner layer is phelloderm a3) together they are called periderm
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3) Bark: layers of cork, cork cambium, and living phloem
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4) sapwood a) active xylem
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5) heartwood a) dead xylem used for support *plant growth review
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