Transport and Plant Structure

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Chapter 37

• Transport and Plant Structure

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• Plant Biology may very well be the oldest branch
  of science
• Plants have been used by man for thousands of
  years
• Lumber
• Food
• Paper
• Medicines

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Introduction To Modern Plant Biology

• Molecular biology is revolutionizing the study of
  plants
• Research on Arabidopsis has given scientists
  insight into the genetic controls of flowering
  and plant development
• By studying plants at the molecular level, plant
  biologists are now understanding how plants work

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The Angiosperm Body

• Angiosperms, or flowering plants, are by far the
  most numerous plants with 275,000 known species
• They are divided into two classes
• Monocots
• Dicots
• There are a number of structural differences
  between these two classes

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The Angiosperm Body

• The typical plant body has three major
  components

Shoot System
Root System
Leaves
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The Root System

• The primary functions of the root system are
• Anchor the plant in the soil
• Absorb water and minerals
• Conduct water and nutrients
• Store food

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• Some plants possess a taproot
• Others possess a fibrous root system
• Most absorption takes place through root hairs
• Some plants even possess roots that protrude
  above ground (adventitious)

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Notice the root hairs on this seedling. Most
water is absorbed into the root through these
hairs.
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The Shoot System

• Vegetative shoots bear leaves
• Floral shoots bear flowers
• Stems are composed of alternating nodes and
  internodes
• Growth of stem may be
• Terminal (terminal bud)
• Axillary (axillary buds)
• The presence of a terminal bud can prevent the
  growth of axillary buds (Apical Dominance)

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Can you identify the nodes and internodes on this
shoot? How might you encourage the lateral buds
to develop?
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Potatoes are actually modified stems called
tubers. Onions are food storage stems known as
bulbs. Can you tell the difference?
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Leaves

• Leaves are the main photosynthetic organs of most
  plants
• Consists of a blade and petiole
• Leaf venation differs between monocots and dicots
• Leaves may be simple, compound, or doubly compound

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Leaf arrangement on the stem may also vary as
shown above
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Major Plant Cell Types

• Parenchyma cells perform most metabolic functions
  for the plant
• Collenchyma cells provide support
• Sclerenchyma cells also support but have thick
  secondary walls
• Xylem cells conduct water upwards
• Phloem cells conduct food both upwards and
  downwards

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Parenchyma cells are the least specialized of
plant cell types
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Collenchyma cells are similar to parenchyma.
However the cell walls are thicker in collenchyma
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These cells are sclerenchyma, the primary
supporting cells of the plant
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Notice the tube-like nature of xylem cells. How
is this related to the function of these cells?
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Phloem cells, like xylem are involved in
transport. How are they different?
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Major Plant Tissues

• Each organ of a plant is comprised of three types
  of tissue
• Dermal tissue surrounds and protects each plant
  part
• Vascular tissue conducts food and water
• Ground tissue comprises most of each organ. It is
  involved in photosynthesis, food storage, and
  support

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Plant Growth

• Most plants continue to grow as long as they
  live.
• Annual plants complete their life cycle within a
  single year or less.
• Biennial plants live for two years, with the
  second year resulting in the development of
  flowers and seeds.
• Perennial plants live for many years. Most
  perennials flower each year after reaching
  maturity.

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Primary Growth

• Primary growth refers to the growth due to
  elongation of the roots and shoots
• Primary growth produces what is known as the
  plant body
• Regions of growth called apical meristems, found
  in both roots and shoots are responsible for this
  primary growth

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This diagram shows the location of the meristem
in a root. What do you suppose the root cap does?
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Secondary Growth

• Secondary growth is growth that results in an
  increase in girth or diameter of the plant
• Wood is the result of secondary growth
• Cylinders of dividing cells called lateral
  meristems are responsible for secondary growth

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Organization of Tissues in Roots
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Stem Growth and Structure
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Leaf Structure and Organization
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Transport of Materials Through the Plant

• The cellular elements of xylem are dead at
  maturity
• Water is absorbed through root hairs primarily by
  osmosis
• Water is transported upwards from cell to cell
  through pits within the cells
• Transpiration-Cohesion Theory is best explanation
  for mechanism responsible.

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• Phloem cells, on the other hand, are living cells
• Sugars and other complex carbohydrates may be
  transported downward to nourish roots and other
  non-photosynthetic parts
• Food may also be stored within the leaves, stems,
  or roots.
• Pressure due to influx of water is responsible
  for movement. Water eventually enters sink cells
  and pressure is reduced

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