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Chapter 36

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					Chapter 36: Transport

 Sections 36-1 through 36-5
        Physical Processes Drive
               Transport
•   Diffusion
•   Osmosis
•   Cohesion
•   Adhesion
•   Evaporation
•   Bulk flow
          Energy Required
• Active transport
• Proton pumps
• Cotransport
Review: Fig. 7-9: Functions of
    Embedded Proteins
          Active Transport
• Energy (ATP) spent

• Against concentration gradient

• Involves specific carriers (transmembrane
  proteins)
       Membrane Potential:
• Voltage across a membrane = difference
  in elec. charge across membrane

• More anions inside, cations outside

• Proton Pumps responsible
         Fig. 7-19: Cotransport
• Active transport of
  one substance that
  drives the transport of
  another

• 1 pump, 2 proteins

• Cotransporter:
  1 “downhill”, 1 “uphill”
  Fig. 36.7: Transport in Plants
• Cation uptake

• Anion uptake

• Sucrose uptake
         Water potential ()
• “sigh”, “psigh”
• Determines direction of movement of
  water
• Water moves from high to low 
•  = S + P

• i.e., solutes & pressure affect 
        Effect of solutes on 
• Solutes always make
   more negative (they
  tie up water
  molecules) (Ch.3)

• Solutions always
  have a negative S
Recall from Ch. 7:
 • Osmosis is a kind of
   diffusion

 • Lower conc. of water
   = negative S
Fig. 36.8:  = S + P
     Fig. 36.8b: Transport Routes
• Important to & from
  vasc. tissue
  – Root cortex
  – Leaf mesophyll
   Fig. 36.12: Lateral Transport
• Root hairs
• Mycorrhizae
• Active transport for
  some nutrients
                 Bulk Flow
= Movement of fluid driven by pressure
• For long-distance transport
• In xylem: tension
  – Role of transpiration
• In phloem: positive pressure
  – Generated by active transport
 Fig. 36.13: Push or Pull in Xylem?
• Root pressure at night

• Guttation: from
  positive pressure in
  xylem

• Minor mechanism
   Fig. 36.15
• “Transpirational Pull”
  creates neg. p

• What if soil water is
  very salty?
          Stomatal opening:
• Guard cells take up water (become turgid)
  – Accumulate K+, water follows
    • Light stimulates proton pumps
    • Low CO2 inside leaf
    • Internal clock
• Guard cells close when:
  – Dark
  – Dry
  – Stressed (via abscisic acid)
  Fig. 36.20:
 Translocation
• Source  sink

• Sieve-tube “loading”
  (active)

• Translocation via
  pressure flow (AKA
  bulk flow)

• “Unloading” at sink
       Fig. 36-19: Cotransport




• Cotransport to load sugars into phloem
• Active transport
Fig. 36.21: Aphid Studies

				
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posted:5/24/2013
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