water roots and stem
TRANSCRIPT
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Transport across
the root and up thestem
Discuss with your
partner
What is diffusion?
30 seconds
What is Osmosis?
30 seconds
What is Active Transport?
30 seconds
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Water uptake by the RootsWater uptake by the Roots
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What are we doing here?
}Another look at the Casparian
Strip
}How water is transported fromroot hair to Xylem
}Transport systems in the Stem
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} Water moves in by osmosis due to lower
water potential inside the epidermal rootcells.
} Minerals taken up by active transport by
the root hair cells.
} This lowers the water potential of these
cells and water moves in.
Water uptake by the RootsWater uptake by the Roots
Low
Watermolecules
High
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Movement of HMovement of H220 through0 throughrootroot
} There are three pathways water can take across the root
tissues:
} The Apoplast pathway water moves through the cellwalls
} The Symplast pathway water moves through thecytoplasm and plasmodesmata
} The Vacuolar pathway water travels from vacuole tovacuole
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} The apoplast is formed by the continuation of the cell
walls, composed of fibrous cellulose (hydrophilic)
TheThe ApoplastApoplast Pathway (90%)Pathway (90%)
however in the Endodermis
} The Casparian strip blocks the apoplast pathway betweenthe cortex and xylem.
} Ensures water and dissolved minerals have to pass throughthe plasma membrane.
} Enables plant to control the rate of water absorption insaturated conditions
at the Xylem
} Minerals and particularly nitrate ions are activelytransported by transporter proteins, into the xylem fromthe cytoplasm of the cortex.
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so, whats that got to do with anything?...
}This lowers the water potential in the xylem so waterenters the xylem from the cortex, by osmosis.
} This osmosis, due to the controlled active transport of
minerals, contributes to ROOT Pressure (c100kPa in the
stem..
(well come back to this)
}Once water enters the xylem it can not pass back into the
cortex as the apoplast pathway is blocked.
TheThe ApoplastApoplast Pathway (90%)Pathway (90%)
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TheThe SymplastSymplast Pathway (10%)Pathway (10%)
} Diffusion of water, -not osmosis
from the root hair, down a water potential
gradient, to the xylem
} Through a continuous cytoplasm?
}
PLASMO
DESM
ATA
of course doh
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Movement of water through the root
SummarySummary
} Read through the statements on worksheet
(page 8) Transport of water into and across the
root.
} Then put the statements in order.
} use a pencil please - pretty please with a
cherry on top ; )
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Up. Up. And AWAY ;)
There are 3 processes that helps water move up the stem:
} Root pressure
} Transpiration pull
} Capillary action
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Told ya, wed come back to it
} Active transport of
minerals into the xylem.
} Water then moves across
the cortex and into thexylem via the water
potential gradient
produced.
} Increasing the volumeof water in the xylem
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Transpiration PullTranspiration Pull
A Good night on the lash
Cohesion:Physical attraction
between like
molecules
} is produced by the loss of water by evaporation fromthe leaves.
} The cohesion between water molecules is strongenough to hold the molecules together in a long chain
or column.
} As molecules are lost at the top of the column, thewhole column is pulled up as one chain transpirationstream.
} The pull from above i.e. evaporation from the leaves,creates a tension in the column of water.
} This is known as the cohesion-tension theory.
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not the one cell thick typedoh
Capillary ActionCapillary Action
} Water molecules are attracted to the sides of the
xylem vessel - adhesion.
} The xylem vessels are narrow, so this can pull the
water up the sides of the vessel.
OOO Charmin ;-)
AA BITaBITa Physics forPhysics for yaya(cause Im Kind)(cause Im Kind)Capillary action occurswhen the forces binding a
liquid together (cohesion
and surface tension) andthe forces attracting thatbound liquid to anothersurface (adhesion) aregreater than the force
of gravity.
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What we have done here! ;-o
}Another look at the Casparian
Strip
}How water is transported fromroot hair to Xylem
}Transport systems in the Stem
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PlenaryPlenary Past Exam QuestionPast Exam Question