Arabidopsis Thaliana

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Arabidopsis Thaliana
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Arabidopsis Mutants
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Effect of Environment of Plant Form
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Angiosperms
Taxonomists divide angiosperms into two
taxonomic classes monocots, which have a
single cotyledon and dicots which have two of
these seed leaves.
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Monocots and Dicots
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Comparison of Monocot and Dicot Plants
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Monocot and Dicot Flowers
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Flowering Plant Morphology
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Root Hairs
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Adventitous Roots
Adventitious roots from the stems of the mangrove
help support and anchor the plant in the
mud. Close-up view shows lenticles which provide
gas exchange and and additional source of oxygen
for the submersed roots.
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Aerial Roots of the Strangler Fig
Aerial roots wrapped around the trunk and limbs
of a swamp tree. Barbados named after this
species due to its bearded appearance.
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Modified Stems
Stolon horizontal stems on the surface
e.g.,strawberries
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Rhizomes - horizontal stems that grow underground
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Tubers swollen ends of rhizomes e.g., potatoes
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Bulbs vertical underground shoots e.g., onions
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Simple verses Compound Leaves
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Modified Leaves
Tendrils cling to supports e.g., honeysuckle
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Cactus spines are modified leaves
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Succulent leaves are modified for storing water
e.g., ice plants
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Poinsettia leaves are brightly colored to attract
pollinators
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Review of Plant Cell Structure
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Plasmodesmata
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Plant Tissues

• Parenchyma
• Least specialized plant cells
• Thin, flexible 10 cell walls
• Most lack 20 cell walls
• Synthesize and store organic food

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Collenchyma

• Lack 20 cell walls.
• 10 cell wall thicker than parenchyma
• and uneven in thickness.
• Living cells that elongate as the stems
• and leaves they support grow.

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Sclerenchyma

• Function in support
• Rigid, thick 20 cell walls
• Cell wall strengthened by lignin
• Lack protoplasts at functional maturity
• Often dead, used as support
• Fibers long, slender, tapered cells in
  bundles
• Sclerids shorter, irregularly shaped cells

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Vascular Tissues
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Xylem

• Trachieds
• Long, thin, tapered cells
• Lignified secondary walls with pits
• Water flows from cell to cell via pits
• Also function in support
• Vessel Elements
• Wider, shorter, thinner walls
• Less tapered
• Aligned end to end
• End walls perforated to form vessels

Both cell types have secondary cell walls Both
dead at functional maturity
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Phloem
Companion cells and sieve cells

• Sieve-tube members - chains of phloem cells that
  transport sucrose, other organic compounds and
  minerals
• Alive at functional maturity, lack nucleus,
  ribosomes and vacuole
• End walls (sieve plates) have pores
• Companion cell connected by plasmodesmata

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Phloem
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Dermal, Vascular and GroundTissue
Each organ of a plant (leaf, stem and root) has
three tissue systems dermal, vascular and
ground. Each is continuous throughout the plant
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• Vascular tissue
• Xylem and phloem that functions in transport
  and support

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• Dermal tissue (epidermic)
• Single layer of tightly packed cells covering and
  protecting the young parts of the plant.
• Root hairs are extensions of the dermal tissue at
  the root tip
• Waxy cuticle is secreted by epidermal cells

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• Ground tissue (mostly parenchyma)
• Occupies the space between vascular and dermal
  tissue
• Photosynthesis, metabolic functions storage and
  support

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The Three Tissue System
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Plant Growth

• Indeterminate Growth as long as the plant is
  living it will grow
• Does not mean plants will live forever, although
  some live hundreds of years
• Made possible by meristems
• Meristematic cells are unspecialized and divide
  to generate new cells called initials
• Apical meristems found in root tips and shoot
  buds
• Lateral meristems along the lengths of roots and
  shoots
• Primary growth elongation by apical meristems
• Secondary growth increased girth by lateral
  meristems in woody plants

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Meristems
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Morphology of a Winter Twig
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Primary Tissues of Roots
Three primary meristems produce the tissues of
the roots Protoderm gives rise to the
epidermis Procambium forms a stele where
phloem and xylem develop Ground meristem gives
rise to ground tissue, fills the cortex.
Endodermis, single-cell thick, innermost layer of
the cortex, acts as a selective barrier Lateral
roots may sprout from the outermost layer
(pericycle) of the stele of a root
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Primary Growth of a Root
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Lateral Root Formation
Epidermis
Lateral Root
Stele
Cortex
Pericycle
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Lateral Root Formation
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Dicot Root
Phloem
Xylem
Pericycle
Endodermis
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Monocot Root
Xylem
Pith
Phloem
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Monocot verses Dicot Root
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Primary Growth of Shoots

• A dome-shaped mass of cells at the tip of an
  terminal bud
• Meristematic cells develop into an axillary bud
• Growth is the result of both cell division and
  elongation within the internode
• Branches originate at the surface of the shoot
  (contrasting with lateral root formation)

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Terminal Bud and Primary Growth of a Shoot
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Monocot Stem
Vascular Bundle
Ground tissue
Epidermis
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Monocot Vascular Bundle
Bundle cap
Par. cells
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Dicot Stem
Ray of ground tissue connecting pith to cortex
Phloem
Xylem
Pith
Sclerenchyma (fibers)
Cortex
Epidermis
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Dicot Vascular Bundle
Xylem
Phloem
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Monocot verses Dicot Stem
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Leaf Anatomy
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Leaf Anatomy
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Leaf Anatomy
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Stomata
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Modular Construction of a Shoot
Shoots are constructed of a series of modules
produced by the serial development of nodes and
internodes within the shoot apex.
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Secondary Growth
Lateral meristems add girth by producing
secondary vascular tissue and periderm. Vascular
cambium produces secondary xylem and phloem Cork
cambium produces a tough covering (suberin) for
stems and roots (cork, together known as the
periderm) Wood is the accumulation of secondary
xylem cells with thick, lignified walls Older
secondary phloem forms part of the bark
(phloem and periderm) and splits and sloughs off
as the tree increases in girth.
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Production of Secondary Xylem and Phloem by the
Vascular Cambium
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Secondary Growth of a Stem
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Secondary Growth of a Stem
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Anatomy of a Tree Trunk
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Animation of Secondary Growth
Animation
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