PLANT STRUCTURE AND GROWTH

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					Plant Structure and Growth

           Chapter 35

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• Plants with vascular tissue have 3
  structures - roots, shoots, leaves.
• 2 groups of angiosperms, monocots
  and dicots, differ in structures.



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• Structures divided into 2 systems:
  root system (below ground), shoot
  system (above ground).
• Systems rely on one another; roots
  - no chloroplasts - need shoots to
  photosynthesize.

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• Monocots (grasses) - fibrous root
  systems (mat-like).
• Dicots (flowers) - taproot system with
  one large root.
• Most absorption of water and minerals
  occurs near root tips with root hairs -
  increase surface area.

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• Some plants - adventitious roots -
  arise aboveground from stems or
  even from leaves.
• In corn - help to keep plant upright.



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http://homepage.smc.edu/hodson_kent/plant_growth/Angiosperms/ID/3%20root%20systems.jpg
• Stems have nodes - leaves attached,
  internodes - spaces between nodes.
• Where leaves meet stems - axillary
  buds - vegetative branch could form.
• Terminal bud - growth of young shoot
  concentrated.
• If terminal bud present, growth
  happens vertically - apical dominance.



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http://utc.usu.edu/factsheets/CarexFSF/CIG/internodes.jpg




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          Modified shoots

• 1Stolons - “runners” of strawberry
  plants - grow on surface so that
  parent plant can asexually
  reproduce in large numbers.




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• 2Rhizomes (ginger) - horizontal stems -
  grow underground.
• 3Tubers (potatoes) - swollen ends of
  rhizomes specialized for food storage.
• 4Bulbs (onions) - vertical, underground
  shoots consisting mostly of swollen
  bases of leaves that store food.

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Rhizomes
Tubers
Bulbs
• Leaves consist of flattened blade
  and stalk (petiole)
• Some leaves evolved other purposes
  (spines of cacti for defense, leaves
  modified for water storage,
  brightly colored leaves that attract
  pollinators)
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• Each organ of plant - 3 tissue systems:
  dermal, vascular, ground.
• Dermal system consists of epidermis
  (covers, protects)
• Epidermis of leaves, most stems
  secretes waxy coating (cuticle) - helps
  parts of plant retain water.

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http://www.naturescapes.net/042004/Figure3.jpg




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• Vascular tissue involved in transport of
  materials between roots and shoots.
• 1Xylem – tissue that conducts water and
  minerals from roots to rest of plant.
• 2Phloem transport nutrients, especially
  carbohydrates produced in leaves down
  stem.

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• 2 types of xylem cells: vessel
  elements, tracheids.
• Dead at maturity - help to thicken
  walls to promote water flow.
• Tracheids - long, thin cells with
  tapered ends.
• Vessel elements - wider, shorter,
  thinner walled, less tapered than
  tracheids.
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• 2 types of phloem cells - companion
  cells, sieve tube members.
• Sieve tube members - tubes that
  material moves through.
• Companion cells assist sieve tube
  members.

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• Ground tissue - tissue neither
  dermal nor vascular.
• Dicot stems, ground tissue divided
  into pith, internal to vascular
  tissue, and cortex, external to
  vascular tissue.

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http://wpcontent.answers.com/wikipedia/commons/thumb/9/92/Stem-histology-cross-section-tag.svg/250px-Stem-histology-cross-section-tag.svg.png




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• 3 different types of plant cells:
  parenchyma, collenchyma, and
  sclerenchyma.
• Parenchyma cells - primary walls
  that are relatively thin and
  flexible; typical plant cells; ex.
  sieve-tube members.
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• Collenchyma cells -thicker primary
  walls than parenchyma cells - used
  for support in growing plants.
• Sclerenchyma cells also function as
  supporting elements of plant.
     Growth of tissues in plants

• Annual plants complete life cycle in
  single year or less.
• Biennial plants - 2 years.
• Plants that live many years,
  including trees, shrubs, and some
  grasses, are perennials.

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http://www.btinternet.com/~micka.wffps/foxglove12.jpg




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• Growth in plants due to embryonic cells
  (meristems)
• Elongate and differentiate into cell
  types depending on tissue of plant.




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http://pgjennielove.files.wordpress.com/2008/06/apical_meristem.png




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• Apical meristems found at tips of
  roots, stems - allow for growth in
  length - only happens at tips.
• Primary growth occurs lengthwise,
  secondary growth - widthwise.
• Lateral meristems responsible for
  secondary growth.
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• Root tip protected by root cap to
  protect meristem.




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• Axillary buds have potential to
  form branches of shoot system.
• Vascular tissue runs length of stem
  in strands (in vascular bundles)



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• Leaf epidermis composed of cells tightly
  locked together.
• Full of stomata - controlled by guard
  cells around that can open and close
  opening.




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• Spongy layer of cells inside leaf has
  chloroplasts with air spaces around
  cells.
• Palisade layer in leaf has densely
  packed cells spread over large
  surface area.

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         Lateral meristems

• 2 cambiums responsible for
  secondary growth.
• Vascular cambium - meristem to
  produce secondary xylem and
  secondary phloem.
• Cork cambium - meristem for tough,
  thick covering for stems and roots
  - replaces the epidermis.
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• As secondary growth continues over
  years, layer upon layer of secondary
  xylem accumulates, producing wood.
• Actually dead cells.
• Growth in areas like Maine occur in
  cycles - dormancy then growth -
  produce growth rings.
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• Bark - all tissues external to
  vascular cambium (secondary
  phloem, cork cambium, cork)
• 2 types of secondary phloem:
  heartwood and sapwood.
• Heartwood (hardwood) no longer
  conducts water; sapwood
  (softwood) functions in transport
  of water and minerals.
                                          Qu i ckTi me ™ an d a
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posted:6/26/2012
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