Chapter 30 Plant Nutrition and Transport

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Chapter 30 Plant Nutrition and Transport
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Nutrients and Their Availability in Soils

• Nutrients are elements needed for growth and
  survival
• Big three elements are oxygen, hydrogen, and
  carbon
• Thirteen others are taken in water through the
  roots
• Six elements have deemed macronutients (e.g. N,
  K, Ca) seven others are micronutrients (e.g. Cl,
  Fe, Zn)

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Properties of Soil

• Soil consists of particles of minerals mixed with
  humus (dead organisms and their litter)
• Particles come three sizes Sand, silt and Clay
• Clay the smallest holds nutrients as water
  percolates through the soil
• Plants do best in loam, soil with nearly equal
  proportions of the three particle type.

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• Layers of soil can be classified by profile
  properties topsoil, the uppermost, is the most
  essential layer for plant growth.

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Leaching and Erosion

• Leaching refers to the removal of some of the
  nutrients from soil as water percolates through
  it
• Erosion is the movement of land under the force
  wind, running water, and ice.

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How Do Roots Absorb Water and Mineral Ions?

• Absorption Routes
• Water moves from the soil across the root
  epidermis to the vascular cylinder, a column of
  vascular tissue in the center of the root
• Sheetlike layer of cells, the endodermis,
  surrounds the column
• Water-repellant Casparian strip forces water to
  move through the cytoplasm of the cells of the
  endodermis

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• Therefore, membrane transport proteins help
  control the types of absorbed solutes that will
  become distributed throughout the plant
• Most flowering plants also have an exodermis, a
  layer of cells just inside the roots which also
  has a Casparian strip that functions just like
  the one next to the root vascular cylinder

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Specialized Absorptive Structure

• Root hairs, extensions of the root epidermal
  cells, greatly increase the absorptive surface.
• Root nodules of legumes harbor bacteria that
  covert gaseous nitrogen to forms useful in the
  growth of the plants. (Symbiotic relationship
  Mutualism)

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• Mycorrhizae (Fungi growing around plant roots)
  aid in absorbing minerals that are supplied to
  the plant in exchange for sugars, a symbiotic
  relationship that is beneficial to both

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Water Transportation

• Transpiration Defined
• Water moves from roots to stems and then to
  leaves
• Some water is used for growth and metabolism, but
  evaporates into the air by transpiration

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Cohesion-Tension Theory of Water Transport

• Water moves through pipelines called xylem,
  composed of cells (dead at maturity) called
  tracheids and vessel members

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• Cohesion-Tension Theory of water explains water
  movement in plants
• The drying power of air causes transpiration,
  which puts water in the xylem in a state of
  tension leading from leaves to stems to roots.
• Unbroken fluid columns of water show cohesion
  (aided by the hydrogen bonds) they resist
  rupturing as they are pulled upward under tension
• As long as water molecules escape from the plant,
  molecules are pulled up to replace

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How do Stems and Leaves Conserve Water?

• Of the water that moves through the leaf, 90 is
  lost by transpiration, only about 2 percent is
  used during photosynthesis

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Water Conserving Cuticle

• Cuticle is translucent, water impermeable layer
  secreted from epidermal cells
• It coats the outer walls, which are exposed to
  air
• Waxes are embedded in a matrix of cutinm a lipid
  polymer
• The cuticle does not bar the entry of light rays,
  but does restrict water loss, inward diffusion of
  CO2, and outward diffusion of oxygen

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Stomata Controlled Water Loss

• Regulates the passage of water, carbon dioxide,
  and oxygen.
• A pair of guard cells defines each opening
• In sunlight, a drop in carbon dioxide levels in
  the guard cells causes potassium and water to
  move into the guard cells causing them to swell
  (turgor pressure) this creates an opening for
  carbon dioxide entry (a benefit) and water loss
  (detriment)

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• At night, potassium and water move out and the
  guard cells collapse to close the gap and
  conserve water

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How are Organic Compounds Distributed Through
Plants?

• Phloem distributes organic products of
  photosynthesis throughout the plant.
• Sieve tubes cells are alive at maturity and are
  interconnected from leaf to root
• Companion cells also participate in a supportive
  role
• Storage forms of organic molecules (examples
  Starch, fats, and proteins) are unsuitable for
  transport throughout the plant body
• They are therefore converted to more soluble
  forms, sucrose

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Translocation

• Most often used to signify the transport of
  sucrose and other compounds through phloem
• Observations of aphids feeding show that sugars
  inside the sieve tubes are being moved under
  pressure

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Pressure Flow Theory

• Movement of molecules through phloem from sources
  (mostly leaves) to sinks (flowers and fruits)
• According to the pressure flow theory,
  translocation depends on pressure gradients
• Solutes are loaded by active transport into the
  phloem from a source water follows
• As pressure builds in the tubes it pushes the
  surcose-laden fluid out of the leaf into the
  stem, and on to the sink