PLANT STRUCTURE

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PLANT STRUCTURE DEVELOPMENT

• Chapter 35

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Overview

• Roots Underground
• Shoots Leafs Stems
• 3 Tissue types in the above
• Dermal, Vascular, Ground
• 5 Types of Differentiated Plant Cells
• Parenchyma
• Collenchyma
• Sclerenchyma
• Xylem
• Phloem

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Roots

• Multicellular organ
• Anchors plant
• Absorbs water Minerals
• May store sugar starches

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Fibrous Roots vs. Taproots

• Fibrous Roots mat of thin roots that are spread
  just below the roots surface
• Taproots 1 thick, vertical root with many
  lateral roots that emanate from it

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Questions

• Which root type is focused on absorption?
• Which root type is focused on storage?
• Fibrous roots are not efficient absorbers, so
  what structure is responsible for absorption?

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Root Hairs

• Located at the tips of roots
• Dramatically increase the surface area
• Efficient absorption of H2O and minerals
• Mycorrhizae Symbiotic relationship
• Root tips fungus assist in absorption
• Found in vast majority of plants

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Mycorrhizae
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Shoots

• Consist of Stems Leaves
• Plant stuff that is above ground
• Leaves main photosynthetic organ in most plants
• Stems
• Function is to display the leaves
• 2 types of buds (growing parts)
• Terminal (Apical) Bud located at top end of
  stem
• Growth usually occurs at this bud
• Axillary Bud located in the v between leaf
  and stem
• Can potentially form a branch

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Questions

• What is the advantage to a plant to only grow at
  the apical and axillary buds?
• A tree house was built between the stem and a
  branch without axillary buds. The growth rate of
  the apical buds is 2 feet per year, the growth
  rate of the axillary buds is 3 feet per year, and
  the tree house was built at a height of 10 feet.
  What will be the height of the tree house in 10
  years?

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Plant Organs (Leaf, Stem, Roots)

• 3 Tissue types (Ground is on the next slide)
• Dermal
• Cover entire plant
• Protect against water loss
• Called Cuticle in the leaves
• Nonspecific defense mechanism
• Vascular
• Continuous throughout the plant
• Transports material between roots and shoots
• Xylem transports water minerals up from the
  roots
• Phloem transports food from the leaves to rest
  of plant

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Plant Organ Tissue Types

• Ground
• Any tissue that is neither dermal nor vascular
• If the Ground tissue is located inside the
  vascular tissue called pith
• Cortex ground tissue located outside vascular
  tissue

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5 Types of Differentiated Cells

• 1. Paren(chyma) cells Most abundant cell type
• -- Present throughout the plant
• -- perform most of the metabolic functions of
  the plant
• (Photosynthesis Respiration)
• 2. Collen(chyma) cells
• -- Support growing parts of the plant
• -- Grouped into cylinders
• 3. Scleren(chyma) cells
• -- Occupy NonGrowing parts of plant
• -- Tough cell walls for structural support
  

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4th Type of Plant Cells

• 4. Xylem water conducting cells
• -- 2 types Tracheids Vessels
• -- Both types are dead at functional maturity
• -- Tracheids found in ALL vascular plants
• -- Long thin cells with lignin
• -- Water moves through the pits
• -- Vessels found primarily in angiosperms
  (flowering plants)
• -- Have pits perforated end walls for water
  movement

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Vessel Elements Tracheids
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5th Final Type of Plant Cell

• 5. Phloem Sugar other organic compounds
• 2 Types Sieve-tube elements Companion Cells
• -- Both types are alive at functional
  maturity
• Sieve Tubes
• -- Consist of chains of cells
• -- Called sieve-tube element
• -- Highly modified for transport
• -- Lack nucleus, ribosomes, vacuoles

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Phloem Continued

• Besides Sieve Tubes, there are also
• Companion Cells
• Provide for the molecular needs of the sieve-tube
  elements
• Connected to the sieve-tube elements by
  plasmodesmata

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Plant Growth

• Plant growth is indeterminant
• Growth occurs throughout plants life
• Embryonic, developing, and mature organs exist at
  all times during a plants life
• Animal growth is determinant
• Growth ceases after a certain size has been
  reached

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Meristems

• Meristems are perpetually embryonic tissues
• Responsible for indeterminate growth
• Growth occurs only as a result of cell division
  in a meristem
• 2 Types of Meristems
• Lateral Meristem Thickening of shoots or roots
• Thickening is called Secondary Growth
• Apical Meristem tips of roots and in buds of
  shoots
• Sites of cell division
• Allow the plant to grow and lengthen
• Primary Growth when plant grows at apical
  meristems
• Lengthening is called Primary growth

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Primary Growth lengthens

• Root Cap protects delicate meristem of the root
  tip as it pushes through the soil
• Secretes a polysaccharide lubricant
• Root Tip contains 3 zones of cells in various
  stages of growth

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3 Zones in root tip

• Zone of cell division
• Root apical meristem derivatives
• New root cells are produced in this region
• Mitotic divisions
• Zone of elongation
• Cells elongate, sometimes significantly
• Zone of maturation
• Differentiation and functional maturation occurs

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Roots - Primary Growth
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Lateral Roots emerge from the Pericycle (lies
inside the endodermis)
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What about shoots?

• Apical meristem dome of dividing cells at tip
  of terminal bud
• Primary growth (Lengthening)
• Accomplished by cell division and elongation

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Primary Growth in Stems
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How does grass continue growth after mowing?
? Mowing should destroy the apical meristems, so
how would grass continue to grow if there were no
growth areas?
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2 other meristems

• Intercalary
• Primarily in monocots (grasses)
• Response to grazing pressure
• Floral
• Flower growth
• Determinate growth

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Lateral Meristems

• Secondary growth
• Growth in the thickness of the shoot or root
• 2 Types
• Vascular Cambium
• Adds layers of tissue called 2ndary Xylem
  phloem
• Cork Cambium
• Replaces the epidermis with the periderm (thicker
  tougher)

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Secondary Growth

• 2 lateral meristems are responsible for 2ndary
  growth
• Vascular Cambium produces 2ndary xylem (wood)
• Cork Cambrium produces a tough covering that
  replaces epidermis
• Early in secondary growth
• Bark all the tissues outside the vascular
  cambium
• Includes the phloem derived from the vascular
  cambium, cork cambium, tissues derived from
  cork cambium

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Question?

• Why would the diameter of the plant have to
  increase as the plant grows?
• Which diameter grows as a higher rate, xylem or
  phloem? Why?

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Leaves

• Stomata interrupts the underside of the leaf
• Flanked by guard cells open/close the stomata
• Ground tissue is in between upper lower
  epidermis, in the mesophyll
• Ground tissue is composed of parenchyma cells
• Site of photosynthesis are parenchyma cells

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Leaf Cross-Section
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Angiosperms (Flowering Plants)

• Classified by years in life cycle (germination ?
  death)
• Annuals 1 year life cycle
• Biennials 2 year life cycle
• Perennials multiple year life cycle

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Question

• Why would there be spaces in the spongy
  mesophyll?
• Why would there not be spaces in the palisade
  mesophyll?