Transport In Plants

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TransportIn Plants
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Cellular Transport

• Diffusion
• Osmosis
• Facilitated Diffusion
• Active Transport
• Proton Pump

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Cell Transport
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Water Potential

• The physical property predicting the direction in
  which water will flow
• Solute concentration
• Pressure
• water moves from high water potential to low
  water potential

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Water Potential (a)

• Left Side
• Pure Water 0 Water Potential
• Right Side
• Negative Water Potential
• 0 pressure
• - solute (has solutes)
• Water moves to the right

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Water Potential (b)

• Left Side
• Pure Water 0 Water Potential
• Right Side
• 0 Water Potential
• pressure equal to solute conc.
• - solute (has solutes)
• Water is at equilibrium

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Water Potential (c)

• Left Side
• Pure Water 0 Water Potential
• Right Side
• Positive Water Potential
• pressure more than solute conc.
• - solute (has solutes)
• Water moves to the left

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Water Potential (d)

• Left Side
• Pure Water and Negative Tension
• Right Side
• Negative Water Potential
• 0 pressure
• - solute (has solutes)
• Water moves to the left

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Plant Cell Water Movement
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Water Relationships in Plants

• Plasmolysis plasma membrane pulls away from the
  cell wall
• Flaccid limp, no tendency for water to enter
• Turgid water moves in and plasma membrane pushes
  up against cell wall

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Aquaporins

• Specialized proteins that facilitate osmosis
• water moves into/out of cells quicker than
  expected across a membrane

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Tissue Level Transport
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Tissue Level Transport

• Trans-membrane
• across cell wall and cytoplasm
• Symplastic
• across the cytoplasm
• Apoplastic
• across the cell walls

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Long Distance Transport

• Bulk Flow
• the movement of a fluid driven by pressure
• Only moved up plants by a negative pressure (not
  solute concentration)
• Unlike osmosis, moves water and solutes

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Absorption of Water and Minerals
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Absorption of Water and Minerals

• Water and Minerals can move through the epidermis
  to the cortex in two methods
• apoplastic
• symplastic

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Absorption of Water and Minerals

• Endodermis is selectively permeable
• Casparian strip is made of suberin
• Water and minerals cannot enter through the stele
  through the apoplastic pathway. It must enter
  through the symplastic pathway.

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Absorption of Water and Minerals

• Focus on soil --gt epidermis --gt root cortex ---gt
  xylem pathway
• Once inside the stele, the water and minerals
  must shift back to the apoplastic pathway because
  xylem has no protoplast

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Absorption of Water and Minerals

• Focus on soil --gt epidermis --gt root cortex ---gt
  xylem pathway (review)
• Two pathways
• 1. Apoplastic --gt symplastic--gt apoplastic
• 2. Symplastic --gt apoplastic
• Water passes into the stele through symplastic
  route
• Water passes into the xylem through apoplastic
  route

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Transport of Xylem Sap

• Pushing Xylem
• Root Pressure
• caused by active pumping of minerals into the
  xylem by root cells
• Guttation the accumulation of water on the tips
  of the plant

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Transport of Xylem Sap

• Pulling Xylem
• Transpiration
• the evaporative loss of water from a plant
  through the stomata

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Transport of Xylem Sap

• Pulling Xylem
• Cohesion
• Water sticking together
• Adhesion
• Water sticking to the cell wall
• Surface Tension
• negative pressure
• Forms a meniscus (concave shape)
• the more concave / the greater the negative
  pressure

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Transport of Xylem Sap
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Transport of Xylem Sap

• Pulling Xylem
• Cohesion binding together of water molecules
• pulls sap up plants
• Adhesion Water sticking to the cell wall
• fights gravity

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The Control of Transpiration

• Guard Cells
• turgid - open
• flaccid - closed
• Potassium Ions
• active transport of Hydrogen ions out of the cell
  causes Potassium ions to move in

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Stomata

• Open during the day / Closed at night
• first light (blue light receptor)
• depletion of Carbon Dioxide
• internal clock (circadian rhythms)

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Reducing Transpiration

• Small, thick leaves
• Thick cuticle
• Stomata are recessed
• Lose their leaves
• C4 or CAM plants

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Phloem Loading
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Translocation of Phloem

• Phloem loading
• movement of sugars through apoplastic and
  symplastic pathways
• sugar made in mesophyll cells
• pass through other cells to seive tube members
• bundle sheath cells
• parenchyma cells
• companion (transfer) cells

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Translocation of Phloem

• Phloem loading
• chemiosmotic mechanism used to load sucrose from
  the apoplast to the symplast pathway
• used with high levels of sucrose accumulation

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Translocation
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Translocation of Phloem

• Translocation transport of food
• moves from a sugar source to a sugar sink
• Reduces water potential inside sieve tube
  (phloem) and begins to take on water from xylem

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Pressure Flow of Phloem

• Pressure Flow
• Water intake generates a hydrostatic pressure
  near source cell that forces water to lower
  pressure areas near sink cell
• Unloads sugars into sink by active transport
  which makes cells lose water to relieve pressure
• Xylem recycles water