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Plant Structure

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occurs near root tips where tiny root hairs increase surface area for absorption ... this is due to meristems (perpetually embryonic tissues) apical meristems ... – PowerPoint PPT presentation

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Title: Plant Structure


1
Plant Structure
  • Chapter 35

2
3 Basic Plant Organs
  • roots
  • stems
  • leaves

3
Roots
  • functions
  • anchors plant
  • absorbs minerals water
  • occurs near root tips where tiny root hairs
    increase surface area for absorption
  • stores organic nutrients
  • 2 types of root systems
  • taproot one main root with many lateral roots
  • fibrous many small roots grow from the stem
    (adventitious)

4
Stems
  • consist of an alternating system of nodes (points
    at which leaves attached) internodes (stem
    segments between nodes)
  • in angle formed by leaf stem is an axillary bud
    which can become a branch
  • at stem apex is a terminal bud which has apical
    dominance and, thereby, inhibits growth of
    axillary buds
  • types of modified stems stolons, rhizomes,
    tubers, bulbs

5
Leaves
  • main photosynthetic organ
  • consists of blade petiole (stalk)
  • veins can be parallel (monocots) or netlike
    (eudicot)
  • simple versus compound leaves

6
3 Tissue Systems
  • dermal
  • vascular
  • ground

7
Dermal Tissue
  • outer protective covering
  • consists of a single layer of cells (epidermis)
    in nonwoody plants
  • consists of protective tissue layers (periderm)
    in older regions of woody plants
  • epidermis has a waxy cuticle to help prevent
    water loss

8
Vascular Tissue
  • carries out long-distance transport between roots
    and shoots
  • 2 types
  • xylem conveys water dissolved minerals from
    roots to shoots
  • phloem transports organic nutrients from source
    to sink
  • xylem phloem are collectively called the stele
  • in roots, the stele is a solid central cylinder
  • in stems leaves, the stele is divided into
    vascular bundles

9
Ground Tissue
  • tissues that are neither dermal nor vascular
  • if located internal to vascular tissue it is
    called pith
  • if located external to vascular tissue it is
    called cortex

10
Stem Tissue Organization
  • epidermis covers stem
  • vascular tissue runs length in bundles
  • lateral shoots arise from axillary buds
  • vascular bundles converge with root vascular
    cylinder at zone of transition

11
Leaf Tissue Organization
  • epidermis has pores called stomata flanked by two
    guard cells
  • ground tissue (mesophyll) between upper lower
    epidermis
  • palisade upper layer of elongated cells
  • spongy lower layer of loosely arranged cells
  • vascular tissue (veins) enclosed by protective
    bundle sheath cells

12
Types of Plant Cells
  • parenchyma perform metabolic functions
  • collenchyma provide flexible support without
    restraining growth of young parts of plant shoot
  • sclerenchyma provide rigid support have thick
    secondary walls strengthened by lignin
  • tracheids vessel elements found in xylem
  • sieve-tube members make up phloem
  • companion cells serve sieve-tube members

13
Plant Growth
  • Chapter 35

14
Indeterminate Growth
  • plant growth is not limited to an embryonic or
    juvenile stage
  • this is due to meristems (perpetually embryonic
    tissues)
  • apical meristems
  • located at tips of roots and in buds of shoots
  • associated with primary growth (length)
  • lateral meristems
  • cylinders of cells located along length of roots
    stems
  • includes vascular cambium cork cambium
  • associated with secondary growth (girth)

15
Types of Growth
  • primary growth
  • produces primary plant body parts of the root
    and shoot systems produced by apical meristems
  • secondary growth
  • produces secondary plant body growth in
    thickness produced by lateral meristems (vascular
    cambium cork cambium)
  • commences where primary growth has stopped
  • occurs in stems roots process is similar

16
Primary Growth Roots
  • growth occurs just behind the root tip
  • 3 zones
  • division
  • elongation
  • maturation
  • produces epidermis, ground tissue, vascular
    tissue

17
Primary Growth Shoots
  • leaves arise as leaf primordia along flanks of
    apical meristem
  • axillary buds form in meristematic cells at based
    of leaf primordia

18
Secondary Growth
  • vascular cambium
  • cylinder of meristematic cells one cell thick
  • increases circumference thickens
  • lays down secondary xylem phloem
  • cork cambium
  • replaces epidermis produces periderm

19
Plant Development
  • Chapter 35

20
Plant Morphogenesis
  • influenced by
  • plane symmetry of cell division
  • direction of cell expansion
  • positional information
  • homeotic genes

21
Cell Division
  • asymmetrical cell division unequal division of
    the cytoplasm
  • (ex) formation of guard cells
  • preprophase band ring of microtubules that
    predicts the plane of cell division

22
Cell Expansion
  • due to water uptake into vacuole pressure on a
    cell wall that has been weakened by enzymes
  • direction depends on orientation of cellulose
    microfibrils in the cell wall

23
Pattern Formation
  • development of specific structures in specific
    locations is due to
  • positional information in the form of signals
    from neighboring cells
  • regulatory genes called homeotic genes
  • (ex) genetic control of flowering

24
Genetic Control of Flowering
  • involves a developmental phase change
  • juvenile ? adult vegetative ? adult reproductive
  • transition from vegetative growth to flowering is
    associated with the switching on of floral
    meristem identity genes which produce
    transcription factors that convert indeterminate
    vegetative meristems to determinate floral
    meristems
  • floral pattern is controlled by organ identity
    genes ABC model (see next slide)

25
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