The Plant Body

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The Plant Body
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Chapter 24 The Plant Body

• Key Concepts
• 24.1 The Plant Body Is Organized and Constructed
  in a Distinctive Way
• 24.2 Meristems Build Roots, Stems, and Leaves
• 24.3 Domestication Has Altered Plant Form

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Chapter 24 Opening Question

• What are the properties of the kenaf plant that
  make it suitable for papermaking?

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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Plants must harvest energy from sunlight and
  mineral nutrients from the soil.
• Body plans and physiology enable plants to do
  these things.
• They also grow throughout their lifetime they
  can redirect growth to respond to environmental
  opportunities.

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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Two systems of plant vegetative organs
• Root systemanchors plant, absorbs water and
  minerals, stores products of photosynthesis.
  Branching increases surface area.
• Shoot system
• Leavesmain photosynthetic organs
• Stemshold leaves up in the sunlight connect
  roots and leaves

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Figure 24.1 Vegetative Plant Organs and Systems
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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Plant development is influenced by three unique
  properties
• Apical meristems
• Cell walls
• Totipotency of most cells.
• Apical meristems are always embryonic, producing
  new tissues throughout the plants life.

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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Cell walls are a rigid extracellular matrix.
• Plant morphogenesis occurs through changes in the
  plane of cell division at cytokinesis.
• This changes the direction of tissue growth.
• Cytokinesis can be uneven location of the cell
  plate is determined by differentiation signals
  early in mitosis.

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Figure 24.2 Cytokinesis and Morphogenesis
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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Most plant cells are totipotent (can
  differentiate into any kind of cell).
• Plants can readily repair damage caused by the
  environment or herbivores.

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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Two growth patterns are established in the
  embryo
• Apicalbasal axis arrangement of cells and
  tissues along the main axis
• Radial axis concentric arrangement of the tissue
  systems

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Figure 24.3 Two Patterns for Plant Morphogenesis
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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• First division of zygote is uneven sets up
  apical-basal axis and polarity.
• Smaller cell becomes the embryo
• Larger cell becomes a supporting structure
  (suspensor)

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Figure 24.4 Plant Embryogenesis
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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• In eudicots, the cotyledons begin to grow, and a
  shoot apical meristem forms between them.
• At the other end of the embryo, a root apical
  meristem forms.

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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Three tissue systems are established during
  embryogensis
• 1. Dermalforms epidermis, usually one cell
  layer.
• Some cells differentiate
• Stomatapores for gas exchange
• Trichomesleaf hairs, protect from herbivores and
  damaging solar radiation
• Root hairsincrease root surface area

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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Aboveground epidermal cells secrete a waxy
  cuticle.
• Limits water loss, reflects damaging solar
  radiation, barrier against pathogens.

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Figure 24.5 Three Tissue Systems Extend
throughout the Plant Body
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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• 2. Ground tissuebetween dermal and vascular
  tissue Three cell types
• Parenchyma cells
• Collenchyma cells
• Sclerenchyma cells

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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Parenchyma cells
• most abundant
• large vacuoles and thin cell walls
• do photosynthesis
• store protein and starch

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In-Text Art, Ch. 24, p. 510 (1)
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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Collenchyma cells
• elongated
• thick cell walls
• provide support

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In-Text Art, Ch. 24, p. 510 (2)
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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Sclerenchyma cells
• very thick walls reinforced with lignin
• undergo programmed cell death
• cell walls remain to provide support

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In-Text Art, Ch. 24, p. 510 (4)
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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• 3. Vascular tissuethe transport system
• Xylem carries water and minerals from roots to
  rest of plant.

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In-Text Art, Ch. 24, p. 510 (5)
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Concept 24.1 The Plant Body Is Organizedand
Constructed in a Distinctive Way

• Phloem
• living cells
• moves carbohydrates from production sites to
  sites where they are used or stored

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In-Text Art, Ch. 24, p. 511 (1)
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Primary growthlengthening of shoots and roots
  branching.
• Results in nonwoody tissuesherbaceous
• Secondary growthincrease in thickness
• Woody plants have a secondary plant body
  consisting of wood and bark.

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Many vegetative organs have evolved novel roles,
  such as roots or stems that are used to store
  water.
• These are examples of natural selection working
  with what is already present and the interaction
  between evolution and development.

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• When cells divide in meristem tissue, one
  daughter cell can differentiate, the other
  remains undifferentiated.
• Apical meristems result in primary growth cell
  division followed by cell elongation
• Lateral meristems result in secondary growth

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Figure 24.6 Apical and Lateral Meristems (Part 1)
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Figure 24.6 Apical and Lateral Meristems (Part 2)
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Figure 24.6 Apical and Lateral Meristems (Part 3)
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Apical meristems can divide indefinitely, so
  growth of roots and shoots is indeterminate.
• Apical meristems produce primary meristems.

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Root apical meristems
• Daughter cells on the root tip form the root cap
  protects root as it pushes through soil.
• Root cap cells detect gravity and control
  downward growth of the root.
• Above the root cap, three zones result as cells
  divide and mature.

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Figure 24.7 Tissues and Regions of the Root Tip
(Part 1)
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Figure 24.7 Tissues and Regions of the Root Tip
(Part 2)
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Root primary meristems give rise to root tissues
• Protoderm produces the epidermis many epidermal
  cells have root hairs.
• Ground meristem produces the cortex, consisting
  of parenchyma cells and the endodermis.
• Endodermal cells have waterproof suberin in the
  cell walls and can control movement of water and
  mineral ions into the vascular system.

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Procambium produces the vascular cylinder
  (stele), made up of pericycle, xylem, phloem.
• Pericycle has 3 functions
• Tissue within which lateral roots arise.
• Contributes to secondary growth by giving rise
  to lateral meristems.
• Membrane transport proteins export nutrient
  ions into the xylem.

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Figure 24.8 Products of the Roots Primary
Meristems (Part 1)
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Figure 24.8 Products of the Roots Primary
Meristems (Part 2)
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Figure 24.8 Products of the Roots Primary
Meristems (Part 3)
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Angiosperm roots begin to grow as a radicle,
  which develops into the primary root (taproot) in
  eudicots.
• Taproots often store nutrients (e.g., carrots,
  beets, sweet potato).
• Monocots form a fibrous root system roots are
  equal in diameter (e.g., grasses, leeks). Also
  called adventitious roots.
• Some monocots have prop roots to support the
  shoot (e.g., corn, banyan trees).

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Figure 24.9 Root Systems of Eudicots and
Monocots (Part 1)
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Figure 24.9 Root Systems of Eudicots and
Monocots (Part 2)
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Figure 24.9 Root Systems of Eudicots and
Monocots (Part 3)
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Shoots are composed of repeating modules
  (phytomers).
• Each has a node with attached leaves, internode
  (stem section), and one or more axillary buds.
• Shoots grow by adding more phytomers.

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Shoot apical meristem also produces three primary
  meristems, which give rise to shoot tissue
  systems.
• Stems have vascular bundles with xylem, phloem,
  and fibers.
• The bundles have different arrangements in
  eudicots and monocots.

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Figure 24.10 Vascular Bundles in Stems (Part 1)
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Figure 24.10 Vascular Bundles in Stems (Part 2)
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Stem modifications
• Potato tubers are underground stems the eyes
  are axillary buds.
• Many desert plants have enlarged stems that store
  water.
• Strawberry plant runners are horizontal stems
  from which roots grow. If the runners break, new
  plants develop on either side (asexual
  reproduction).

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Figure 24.11 Modified Stems (Part 1)
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Figure 24.11 Modified Stems (Part 2)
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Figure 24.11 Modified Stems (Part 3)
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Growth of leaves is determinate they stop
  growing once they reach a predetermined mature
  size.
• Leaves consist of a blade, attached to the plant
  stem by a petiole.
• Leaves are often oriented perpendicular to the
  suns rays, to maximize the amount of light for
  photosynthesis.

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Leaf anatomy is well adapted to
• Carry out photosynthesis
• Exchange O2 and CO2 with the environment
• Limit evaporative water loss
• Export products of photosynthesis to the rest of
  the plant

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Leaf mesophyll has two zones of photosynthetic
  parenchyma tissue.
• A network of air spaces allows CO2 to diffuse to
  photosynthetic cells.
• Vascular bundles form veins that extend to within
  a few diameters of all cellsto ensure transport
  of water and minerals in and carbohydrates out.

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Figure 24.12 Eudicot Leaf Anatomy
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Leaf surfaces are covered with nonphotosynthetic
  epidermal cells.
• They secrete the waterproof cuticle.
• Water and gases are exchanged through pores
  called stomata.

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Leaves can also be modified for other functions
• Nutrient storage (e.g., onion bulbs)
• Water storage (e.g., in succulent plants)
• Protection (e.g., cacti have spines that are
  modified leaves)
• Tendrils that wrap around structures to support
  climbing plants (e.g., peas)

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Many eudicot stems and roots have secondary
  growth
• Wood and bark are derived by secondary growth
  from the two lateral meristems
• Vascular cambium produces secondary xylem
  (wood) and secondary phloem (inner bark).
• Cork cambium produces waxy-walled protective
  cells some become the outer bark.

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Figure 24.13 A Woody Twig Has Both Primary and
Secondary Tissues (Part 1)
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Figure 24.13 A Woody Twig Has Both Primary and
Secondary Tissues (Part 2)
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Figure 24.13 A Woody Twig Has Both Primary and
Secondary Tissues (Part 3)
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• A stem or root increases in diameter when cells
  of the vascular cambium divide, producing
  secondary xylem cells toward the inside and
  secondary phloem cells toward the outside.
• Some cells of the secondary phloem divide and
  form a cork cambium, which produces layers of
  protective cork.
• The cork soon becomes the outermost tissue of the
  stem or root.

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Cork cambium produces cells to the inside,
  forming the phelloderm.
• Peridermsecondary dermal tissue composed of cork
  cambium, cork, and phelloderm
• Barkperiderm plus secondary phloem

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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• In temperate zones, annual rings form in the
  wood.
• In spring, tracheids or vessel elements tend to
  be large in diameter and thin-walled.
• In summer, thick-walled, narrow cells are
  produced.

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Figure 24.14 Annual Rings
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Concept 24.2 Meristems Build Roots, Stems, and
Leaves

• Monocots do not have secondary growth.
• A few have thickened stems (e.g., palms).
• Palms have a very wide apical meristem that
  produces a wide stem, and dead leaf bases add to
  the diameter of the stem.

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Concept 24.3 Domestication Has Altered Plant Form

• A simple body plan underlies the diversity of
  flowering plant forms.
• Plant body form is subject to natural selection.
• Example some plants have become vines the
  climbing phenotype gives them access to light in
  crowded conditions.

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Concept 24.3 Domestication Has Altered Plant Form

• Humans domesticate crop plants by artificial
  selection for phenotypes best suited for
  agriculture.
• Corn was domesticated from the wild grass
  teosinte, which still grows in Mexico.
• Teosinte is highly branched corn has a single
  shoot. Branching is controlled by a single gene
  that regulates axillary buds.

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Figure 24.15 Corn Was Domesticated from the Wild
Grass Teosinte
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Concept 24.3 Domestication Has Altered Plant Form

• Brassica oleracea (wild mustard) is the ancestor
  of several morphologically diverse crops kale,
  broccoli, brussels sprouts, cabbage.
• Starting with diverse populations of wild
  mustard, humans selected and planted seeds from
  variants with traits they found desirable.

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Figure 15.4 Many Vegetables from One Species
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Answer to Opening Question

• Kenaf grows rapidly, reaching 45 meters in 5
  months.
• There are over 500 known genetic strains.
• Since its domestication, it has been selected to
  grow taller and branch less.
• The adventitious roots have become longer (2
  meters!), and more numerous, promoting growth in
  dense stands.

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Answer to Opening Question

• Kenaf phloem fibers are longer than wood fibers,
  which makes stronger products.
• Cells walls dont have lignin, making it easier
  to pulp.
• A hectare of kenaf produces 3 times more fiber
  than a hectare of southern pine (which takes 20
  years to grow).

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Figure 24.16 Kenaf Stems