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/A
ngiosperms/ID/320root20systems.jpg
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• 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/interno
des.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
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Tubers
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Bulbs
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• 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/thu
mb/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.

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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.
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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/ap
ical_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.

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