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Transport in Plants. Transport in plants. H 2 O & minerals transport in xylem transpiration evaporation, adhesion & cohesion negative pressure Sugars transport in phloem bulk flow Calvin cycle in leaves loads sucrose into phloem positive pressure Gas exchange photosynthesis

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Presentation Transcript
transport in plants
Transport in plants
  • H2O & minerals
    • transport in xylem
    • transpiration
      • evaporation, adhesion & cohesion
      • negative pressure
  • Sugars
    • transport in phloem
    • bulk flow
      • Calvin cycle in leaves loads sucrose into phloem
      • positive pressure
  • Gas exchange
    • photosynthesis
      • CO2 in; O2 out
      • stomates
    • respiration
      • O2 in; CO2 out
      • roots exchange gases within air spaces in soil

Why doesover-wateringkill a plant?

ascent of xylem fluid
Ascent of xylem fluid

Transpiration pull generated by leaf

water mineral absorption
Water & mineral absorption
  • Water absorption from soil
    • osmosis
    • aquaporins
  • Mineral absorption
    • active transport
    • proton pumps
      • active transport of H+

aquaporin

root hair

proton pumps

H2O

mineral absorption
Mineral absorption
  • Proton pumps
    • active transport of H+ ions out of cell
      • chemiosmosis
      • H+ gradient
    • creates membranepotential
      • difference in charge
      • drives cation uptake
    • creates gradient
      • cotransport of othersolutes against theirgradient
water flow through root
Water flow through root
  • Porous cell wall
    • water can flow through cell wall route & not enter cells
    • plant needs to force water into cells

Casparian strip

controlling the route of water in root
Controlling the route of water in root
  • Endodermis
    • cell layer surrounding vascular cylinder of root
    • lined with impermeable Casparian strip
    • forces fluid through selective cell membrane
      • filtered & forced into xylem cells

Aaaah…

Structure–Functionyet again!

root anatomy
Root anatomy

dicot

monocot

mycorrhizae increase absorption
Mycorrhizae increase absorption
  • Symbiotic relationship between fungi & plant
    • symbiotic fungi greatly increases surface area for absorption of water & minerals
    • increases volume of soil reached by plant
    • increases transport to host plant
transport of sugars in phloem
Transport of sugars in phloem
  • Loading of sucrose into phloem
    • flow through cells via plasmodesmata
    • proton pumps
      • cotransport of sucrose into cells down proton gradient
pressure flow in phloem
Pressure flow in phloem
  • Mass flow hypothesis
    • “source to sink” flow
      • direction of transport in phloem is dependent on plant’s needs
    • phloem loading
      • active transport of sucrose into phloem
      • increased sucrose concentration decreases H2O potential
    • water flows in from xylem cells
      • increase in pressure due to increase in H2O causes flow

can flow 1m/hr

On a plant…What’s a source…What’s a sink?

experimentation
Experimentation
  • Testing pressure flow hypothesis
    • using aphids to measure sap flow & sugar concentration along plant stem
slide15

Don’t get mad…

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Ask Questions!

control of stomates
Control of Stomates

Epidermal cell

Nucleus

Guard cell

Chloroplasts

  • Uptake of K+ ions by guard cells
    • proton pumps
    • water enters by osmosis
    • guard cells become turgid
  • Loss of K+ ions by guard cells
    • water leaves by osmosis
    • guard cells become flaccid

K+

K+

H2O

H2O

H2O

H2O

K+

K+

K+

K+

H2O

H2O

H2O

H2O

K+

K+

Thickened inner

cell wall (rigid)

H2O

H2O

H2O

H2O

K+

K+

K+

K+

Stoma open

Stoma closed

water moves into guard cells

water moves out of guard cells

control of transpiration
Control of transpiration
  • Balancing stomate function
    • always a compromise between photosynthesis & transpiration
      • leaf may transpire more than its weight in water in a day…this loss must be balanced with plant’s need for CO2 for photosynthesis