Transport in Vascular Plants

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Chapter 36

• Transport in Vascular Plants

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• Physical forces drive the transport of materials
  in plants over a range of distances
• Transport in vascular plants occurs on three
  scales
• Transport of water and solutes by individual
  cells, such as root hairs
• Short-distance transport of substances from cell
  to cell at the levels of tissues and organs
• Long-distance transport within xylem and phloem
  at the level of the whole plant

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• A variety of physical processes
• Are involved in the different types of transport

CO2
O2
Light
H2O
Sugar
Sugars are transported as phloem sap to
roots and other parts of the plant.
O2
H2O
CO2
Minerals
Figure 36.2
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Selective Permeability of Membranes A Review

• The selective permeability of a plant cells
  plasma membrane controls the movement of solutes
  into and out of the cell
• Specific transport proteins enable plant cells to
  maintain an internal environment different from
  their surroundings

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The Central Role of Proton Pumps

• Proton pumps in plant cells
• Create a hydrogen ion gradient that is a form of
  potential energy that can be harnessed to do work
• Contribute to a voltage known as a membrane
  potential

Figure 36.3
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• In the mechanism called cotransport
• A transport protein couples the passage of one
  solute to the passage of another

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• The effect of cotransport is also responsible for
  the uptake of the sugar sucrose by plant cells

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• Water Potential
• Is a measurement that combines the effects of
  solute potential and pressure potential
• Determines the direction of movement of water
• Water flows from regions of high water potential
  to regions of low water potential

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• How Solutes and Pressure Affect Water Potential
• The solute potential of a solution
• Is proportional to the number of dissolved
  molecules
• Pressure Potential
• Is the physical pressure on a solution

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• The addition of solutes reduces water potential

Figure 36.5a
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• Application of physical pressure increases water
  potential

Figure 36.5b, c
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• Negative pressure
• Decreases water potential

Figure 36.5d
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• Water potential
• Affects uptake and loss of water
• by plant cells
• If a flaccid cell is placed in an
• environment with a higher solute
• concentration the cell will lose
• water and become plasmolyzed

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• If the same flaccid cell is placed in a solution
  with a lower solute concentration the cell will
  gain water and become turgid

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• Turgor loss in plants causes wilting which can be
  reversed when the plant is watered

Figure 36.7
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Compartments of Plant Cells and Tissues and Three
Routes for Short-Distance Transport
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Lateral Transport of Minerals and Water in Roots
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The Fungal Hyphae of Mycorrhizae Increase the
Absorption of Water and Minerals
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Aquaporin Proteins and Water Transport

• Aquaporins
• Are transport proteins in the cell membrane that
  allow the passage of water
• Do not affect water potential

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• The plasma membrane
• Directly controls the traffic of molecules into
  and out of the protoplast
• Is a barrier between two major compartments, the
  cell wall and the cytosol

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• Water and Minerals Ascend From
• Roots to Shoots Through the Xylem

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• Transpiration produces negative pressure
  (tension) in the leaf which draws water out of
  the xylem into the mesophyll

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The Generation of Transpirational Pull in a Leaf
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Ascent of Water in a Tree
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The Mechanism of Stomatal Opening and Closing
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The Diffusion of K Ions Into and Out ofthe Guard
Cells Opens and Closes the Stomata
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An open (left) and closed (right) stoma of a
spider plant (Chlorophytum colosum) leaf
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• Review
• As water ascends up a tree water
• potential decreases/increases.
• 2) A beaker of pure water open to the
• atmosphere has a water potential of . . . A
  flaccid cell placed in this solution would become
  . . .

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3) A turgid cell is placed into a solution with
a high solute concentration. The pres- sure
remains unchanged. What happens to water
potential inside the cell? 4) Discuss the
movement of K ions in guard cells that would
occur during a 24 hour period on a typical hot
summer day.