23.1 Specialized Tissues in Plants

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23.1Specialized Tissues in Plants

• Essential Question
• What are plant tissues and organs?

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Seed Plant Structure

• Three main organs of seed plants are roots,
  stems, and leaves
• These organs are linked together by systems that
  transport nutrients, protect it, and coordinate
  activities

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Roots

• Absorb and transport water and dissolved
  nutrients to rest of plant
• Anchor plant in ground, holding soil in place,
  and preventing erosion
• Keeps plants upright against forces such as wind
  and rain
• Protects plant form harmful soil bacteria and
  fungi
• Two types fibrous and taproot

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Stems

• Have three important functions
• Produce leaves, branches, and flowers
• Hold leaves up to sunlight
• Transport substances between roots and leaves

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Leaves

• Principle organs in which plants carry out
  photosynthesis
• Vary widely according to species
• Have adjustable pores called stomata that help to
  conserve water and exchange gases

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Tissue Systems- 3 types

• Dermal outermost layer of cells functions to
  protect plant and exchange gases and water
• Ground cells that lie between the dermal and
  vascular systems
• Vascular transports water and nutrients
  throughout plant

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Dermal Tissue

• Outermost layer of plant
• Consists of single layer of epidermal cells
• Often covered with waxy layer called the cuticle
  that protects against water loss and injury

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Dermal Contd

• Some cells have projections called trichomes that
  help protect leaf and give it a fuzzy appearance
• Root dermal tissue contains root hair cells that
  aid in absorption

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Dermal Contd

• Underside of leaves have stomata which contain
  guard cells that regulate water loss and gas
  exchange

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Leaf Structure
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Vascular Tissue

• Forms transport system m conducts water and
  nutrients through plant
• Made up of a network of hollow connected cells
• Consists of
• xylem (water-conducting tissue)
• consists of tracheids (conifers) and vessel
  elements (angiosperms only)
• phloem (food conducting tissue).
• Phloem consists of sieve tube elements and
  companion cells

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Tracheids

• Found in all seed plants
• type of xylem cell
• Found first in fossil record
• Only xylem cell found in conifers and ferns
• long, narrow cells with walls made of lignin and
  cellulose that are impermeable to water
• Walls are pierced with openings that connect them
  to other cells
• Mature cells die and cytoplasm disintegrates

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Vessel elements

• Only found in angiosperms
• Conduct water
• much wider than tracheids and are arranged end to
  end like stacked tin cans
• Angiosperms have both tracheids and vessel
  elements but rely on vessel element to move water
• Both types of cells mature and die before they
  can conduct water

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Compare Vessel element and Tracheid
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Phloem

• Phloem tissue transports carbohydrates made
  during photosynthesis.
• Made of sieve tube elements and companion cells
• sieve tube elements are arranged end to end to
  form sieve tubes
• Sieve tubes are mature cells that die and lose
  nuclei and most organelles
• remaining organelles hug cell wall to form
  pipeline for movement of fluids.

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Contd

• Ends of sieve tubes have many small holes to
  allow movement of sugars and other foods
• Companion cells surround sieve tube elements and
  help support phloem cells and aid in movement of
  substances in and out of phloem

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Xylem and Phloem Vessel
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Cross Section of a Stem
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Ground Tissue

• Made up of cells that lie between dermal and
  vascular tissues
• Site of photosynthesis helps support plants
• May have three types of cells (depending on plant
  type)
• parenchyma cells thin cell walls and large
  central vacuole in leaves are packed with
  chloroplasts
• Function in storage and photosynthesis
• collenchyma cells have thick strong flexible cell
  walls that help support larger plants
• sclerenchyma cells have extremely thick, rigid
  cell walls that make ground tissue tough and
  strong.
• Both collenchyma cells and sclerenchyma cells
  function as support

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Types of Cells in Ground Tissue
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Meristematic Tissue

• Meristems are clusters of meristematic cells
  (undifferentiated cells) that are found in zones
  of the plant and help it grow throughout its
  entire life
• Its function is to begin growth of new cells in
  seedlings at the tips of roots and shoots
• Meristematic tissue produces meristems
  (meristematic cells) that are not yet specialized
  to perform specific functions (undifferentiated
  or embryonic)
• Meristematic tissue is the only plant tissue that
  produces new cells by mitosis
• Classified by location in plant
• apical meristems found at the end or tip of
  growing roots and stems (shoots)
• Lateral meristems -- found in the vascular
  cambium and cork cambium
• intercalary meristems -- at internodes, or stem
  regions between the places at which leaves attach

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Plant Tissue Types
Dermal tissue
Vascular tissue
Ground tissue
Meristematic tissue
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Meristematic Tissue
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Root Meristem
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Differentiation

• At first cells in meristem look alike
• Then they divide rapidly and mature in a process
  called differentiation
• Cells develop into each of the tissue systems of
  the plant (dermal, ground, and vascular)