Cells and Tissues

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Cells and Tissues

• Chapter 24

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Tissues

• Tissues are groups of cells performing a common
  function. Tissues are specialized.
•  Main tissues are dermal tissue systems, ground
  tissues, and vascular tissues.

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Primary Growth Meristems

• Apical meristems
• Location Tips of roots and stems.
• Function Produce primary growth which results in
  increase in length.
• Produce three primary meristems protoderm,
  procambium, and ground meristem.
• Young buds and leaves are produced by apical
  meristems, roots by root meristems.

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Secondary growth meristems lateral meristems

• Vascular cambium
• Location Thin, branching cylinder that runs the
  length of the roots and stems of most perennial
  and some herbaceous annuals.
• Function Produces increase in girth (width).
• Cork cambium
• Location Exterior of the vascular cambium.
  Similar in structure to the vascular cambium
  forming a thin ring in the roots and stems.
• Function Produces outer bark of woody plants.

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Shoot and Root Apical Meristem Tissues A) Lilac
shoot B) Radish root
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Nonmeristematic Tissues

• Cells produced by meristematic tissues that
  assume a defined shape and size related to their
  specific function.
• Simple Tissues Composed of one type of cell
  performing a specific function.
• Collenchyma, Parenchyma, and Sclerenchyma-Ground
  tissues
• Parenchyma is the most common type

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Parenchyma

• Location Found in all parts of higher plants
• Description Many sided, thin walled, alive at
  maturity no secondary wall most have large
  vacuoles containing starch, oil, tannins,
  crystals, and other secretions.
• Function Food or water storage.
• Edible part of most fruits and vegetables is this
  type of tissue.

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Transfer Cells- A type of Parenchyma with
ingrowths Facilitate movement of solutes
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Collenchyma

• Description Similar to parenchyma (alive, no
  secondary wall) but have unevenly thickened
  walls.
• Location Usually occur just beneath the
  epidermis layer.
• Function in providing flexible support to leaves
  and flowers.

Rhubarb collenchyma from petiole
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Parenchyma (below) and Collenchyma (above) Note
the difference in cell wall size
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Sclerenchyma

• Description Cells with tough, thick secondary
  cell walls, usually strengthened with lignin.
  Cells are dead at maturity.
• Function is support and strength.
• Two types of sclerenchyma are found in plants
• 1) sclereids may be found scattered throughout
  various types of tissues (seed coats, nut shells,
  stony endocarps, pear fruit)
• 2) fibers are long cells with a small cavity
  (lumen) in the center. Over 40 types of fibers
  are used in commercial use in manufacturing
  textiles and similar products.

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Sclereid type of sclerenchyma
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Sclerenchyma-sclereids From water lily
Sclereids from Peach
Sclerenchyma-fibers from Basswood
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Nonmeristematic tissues

• Complex tissues Composed of two or more kinds of
  cells performing a specific function. Four main
  types found in plants.
• Xylem-Water conducting tissue
• Phloem-Sugar conducting tissue
• Epidermis-outer skin
• Periderm-replaces epidermis in woody plants

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Xylem-Complex tissue

• Description Consists of a combination of
  parenchyma cells, fibers, tracheary elements
  (vessel elements and tracheids) and ray cells.
• Function Plumbing of the plant. Moves water and
  dissolved substances throughout the plant
• Location in vascular bundles with phloem

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Tracheary Elements

• Dead at maturity, thick secondary cell walls,
  openings allow water to move through
• Vessel elements consist of long tubes of
  individual vessel cells which are hollow with
  open bars at the end of the cell. Cells are
  joined at the ends. Various types of secondary
  wall thickenings (annular, helical, etc)
• Tracheids. Tapered at the ends. Do not have
  openings at the ends. Overlap where they touch,
  pits in the cell wall allow water movement.
• Tracheids found in gymnosperms Vessel elements
  and tracheids found in angiosperms

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Xylem

• Vessels and tracheids are responsible for the up
  and down movement of water.
• Ray cells move water laterally. Ray cells are
  produced by the vascular cambium and radiate out
  from the center of stems and roots.

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Vascular bundle from Squash
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Secondary xylem (wood) from Oak a-c Vessel
elements, d tracheid e-ffibers
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Development of vessel element from
undifferentiated cell
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Phloem-Complex tissue

• Description Derived from vascular cambium.
  Includes sieve elements, fibers, parenchyma
  cells, and ray cells. Composed of sieve-tube
  elements and companion cells in angiosperms.
• Function the movement of dissolved food
  substances.

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Development of sieve-tube element from
undifferentiated cell
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Rendition of phloem in an angiosperm
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Sieve-tube elements

• Sieve-tube elements are laid end to end. They do
  not have large openings but instead, have many
  small pores in the the ends (Sieve-plates). The
  cytoplasm of the cells extend through the pores
  and are in contact with the adjacent cells
  cytoplasm.

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Phloem

• Companion cells do not directly transport
  dissolved food substances but control the
  activities of sieve-tube elements. Sieve-tube
  elements do not have nuclei.
• Can repair themselves if damaged by producing
  callose, which in combination with a protein,
  plugs any holes in the phloem. This is usually in
  response to insect damage.
• Sieve-cells, found in ferns and conifers, are
  similar to sieve-tube members but do not form
  continuous tubes but overlap much as in the same
  manner as tracheids. Also do not have nuclei.
  Have albuminous cells which function as companion
  cells.

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Sieve-tube elements and companion cells Example
from an angiosperm
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Sieve Cells and albuminous cells Example from a
gymnosperm
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Development of sieve-tube elements in squash
(angiosperm)
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Epidermis-Complex Tissue

• Location Outer layer of cells, one cell thick.
• Function Exchange material with the environment
  and protect internal cells.
• Epidermal cells secrete cutin on the surface of
  the outer walls. Cutin forms the cuticle or waxy
  layer that prevents the leaf from drying out.
• On leaves, four types of specialized epidermal
  cells. Small pores, called stomata, which are
  bordered by guard cells.
• Trichomes include microscopic extensions called
  root hairs which increase the absorptive surface
  of the root, hairs, and glands which secrete
  substances.

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Trichome on a leaf and stomata
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Periderm

• Function Replaces the epidermis on woody plant
  stems. Protects the internal tissues.
• Location Outer bark of the plant
• Description Consists primarily of cork cells.
  These cells are rectangular, boxy cells which are
  dead at maturity. Before they die, the cork cells
  secrete suberin, a waxy substance, which repels
  water.
• Where suberin is not laid down, there are loosely
  arranged pockets of cork cells. These are
  lenticels and function to allow gas exchange from
  the stem with the atmosphere.

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Transverse section of periderm from apple stem
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Lenticel