Transcript Water Transport in Plants

Water Transport in Plants
Getting water to the leaves
• The leaves need the water to perform
photosynthesis without water no
photosynthesis. Without photosynthesis
the plant will die.
• But the leaves can be hundreds of meters
from the root where most of the water
uptake occurs
Back to water properties
Remember…….
Cohesion
• Cohesion = water
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molecules are
attracted to other
water molecules
Due to Hydrogen
Bonds – polarity of
water molecule
Could be broken by a
surfactant - soap
Adhesion
• Water molecules
attracted to other
substances
– Example glass
Root Pressure
• Dew occurs when the roots continue to take in
mineral and the rate of transpiration is low
– When is transpiration low?
Root Pressure
• Pressure is created by the xylem
– Dissolved minerals are present in the root cells (get
there from active transport) increases the solute
concentration inside the cell, thus water enters
through osmosis creating pressure forcing the fluid up
the xylem
– Thus, water is forced from the high pressure in the
roots to the low pressure in the leaves.
– Can only push water a maximum of a few meters
Transpiration
• What the plants over a few meters tall use to
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transport the water to the leaves
Pulls the water up the stem
Adhesion and cohesion help transpiration
(which occur at the stomata and lenticels)
sucks the water up the xylem
Transpiration
• As water is lost in the leaves and stem it must
•
be replaced transpiration allows that to
happen
Depends on temperature
– High temp = lots of transpiration water can raise
75cm per minute
– Low temperature = transpiration rate slower
Sugar Transport
• Phloem moves the sugar from the leaves to the
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rest of the plant
Movement from source to sink
Glucose moved by active transport into the
phloem (via the companion cells) water enters
by osmosis
Animation
Sugar Transport
• Increase water pressure pushes the water and
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sugar though the phloem to the rest of the plant
-- pressure flow theory
Sugars transported actively into the cells
Water also leaves the cell
Animation Links
• Transpiration