Specialized Tissue in Plants

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Specialized Tissue in Plants

• Chapter 23

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Seed Plant Structure

• Three of the principal organs of seed plants are
  roots, stems, and leaves.
• These organs are linked together by systems and
  subsystems that run the length of the plant.
• They perform functions such as transport and
  protection and coordinating plant activites.

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Importance of Roots

• The root system of a plant absorbs water and
  dissolved nutrients.
• Roots anchor plants in the ground, holding soil
  in place and preventing erosion.
• They transport water to the rest of the plant,
  and hold plants upright against the forces of
  wind and rain.

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Types of Roots

• The two main types of roots are taproots, which
  are found mainly in dicots, and fibrous roots,
  which are found mainly in monocots.
• A taproot is a primary root that grows long and
  thick in the downward direction, while the
  secondary roots remain small.
• Carrots, dandelions, beets, and radishes have
  short thick taproots that store sugars and
  starches.

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Taproot
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Roots

• Fibrous roots are roots that branch to an
  extent that no single root grows longer than the
  rest.
• This type of branching prevents topsoil from
  eroding or from being washed away from heavy
  rains.
• Fibrous roots are very commonly found in plants
  such as grasses.

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Fibrous Roots
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Importance of Stems

• In general, stems have three important functions
  
• They produce leaves, branches, and flowers.
• They hold leaves up to the sunlight.
• They transport substances between roots and
  leaves.

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Types of Stems

• In monocots, vascular bundles are scattered
  throughout the stem.
• The cross section of a young monocot stem shows
  all three tissue systems clearly.
• The stem has a distinct epidermis, which encloses
  a series of vascular bundles, each of which
  contains xylem and phloem.
• Phloem faces the outside of the stem, and xylem
  faces the center.
• These bundles are scattered throughout the ground
  tissue.

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Monocot Stem
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Types of Stems

• In dicots and most gymnosperms, vascular bundles
  are arranged in a cylinder.
• The epidermis surrounds the outermost portion of
  the stem, followed directly by the cortex.
• The cortex contains a ring of vascular bundles.
• The entire center of a dicot stem, is filled with
  pith tissue.

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Dicot Stem
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Formation of Wood

• Most of what we call wood is actually layers of
  xylem.
• They build up year after year, layer on layer.

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Wood
Bark
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Leaves

• The leaves of a plant are its main organs of
  photosynthesis.
• The structure of a leaf is optimized for
  absorbing light and carrying out photosynthesis.
• To collect sunlight, most leaves have thin,
  flattened sections called BLADES.
• The blade is attached to the stem by a thin stalk
  called a petiole.

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Parts of a leaf

• A. Blade 1.
  Veins 2. Margin
• B. Petiole

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Leaf Margins
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Leaves and Vascular Tissue

• The blades of leaves may be covered by a tough
  outer waterproof coating called a cuticle.
• The vascular tissue of leaves are connected
  directly to the vascular tissues of stems, making
  them part of the plants transport system.
• In leaves, xylem and phloem tissues are gathered
  together into bundle that run from the stem into
  the petiole.

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Leaves and Vascular Tissue
Cuticle
Veins
Epidermis
Palisademesophyll
Xylem
Vein
Phloem
Spongymesophyll
Epidermis
Stoma
Guardcells
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Transpiration

• The surfaces of spongy mesophyll cells are kept
  moist so that gases can enter and leave the cells
  easily.
• This also means that water evaporates from these
  surfaces and is lost to the atmosphere.
• Transpiration is the loss of water through
  leaves.
• This lost water is replaced by water drawn into
  the leaf through xylem vessels in the vascular
  tissue.