Download Plant resources and transport

How can trees be so tall...and get water to
their tops?
AP Biology
Also, check out the Bioflix on
water transport
AP Biology
Transport in
Plants
AP Biology
2006-2007
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

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respiration
 O2 in; CO2 out
 roots exchange gases within air spaces in soil
Why does
over-watering
kill a plant?
Ascent of xylem fluid
Transpiration pull generated by leaf
AP Biology
Control of Stomates
Guard cell
Epidermal cell
 Uptake of K+ ions
by guard cells



proton pumps
water enters by
osmosis
guard cells
become turgid
H2O
K+
H2O
K+
 Loss of K+ ions
Nucleus
Chloroplasts
H2O
K+
H2O
K+
K+
H2O
K+
H2O
K+
H2O
K+
H2O
Thickened inner
cell wall (rigid)
by guard cells


AP Biology
water leaves by
osmosis
H2O
K+
guard cells
become flaccid
H2O
K+
H2O
K+
H2O
K+
Stoma open
Stoma closed
water moves
into guard cells
water moves out
of guard cells
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
AP Biology
Water & mineral absorption
 Water absorption from soil
osmosis
 aquaporins

 Mineral absorption
active transport
 proton pumps

 active transport of
H+
aquaporin
root hair
AP Biology
proton
pumps
H2O
Mineral absorption
 Proton pumps

active transport of H+ ions out of cell
 chemiosmosis
 H+ gradient

creates membrane
potential
 difference in charge
 drives cation uptake

creates gradient
 cotransport of other
solutes against their
gradient
AP Biology
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
AP Biology
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–Function
yet again!
AP Biology
Root anatomy
dicot
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monocot
Mycorrhizae increase absorption
 Symbiotic relationship between fungi & plant



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symbiotic fungi greatly increases surface area for
absorption of water & minerals
increases volume of soil reached by plant
increases transport to host plant
Mycorrhizae
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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
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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
AP Biology
On a plant…
What’s a source…What’s a sink?
can flow
1m/hr
Experimentation
 Testing pressure flow
hypothesis

using aphids to measure sap
flow & sugar concentration
along plant stem
AP Biology
Maple
sugaring
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Any Questions?
AP Biology
REVIEW
1. How does transport differ going up
versus going down in plants?
2. Why do roots look like roots?
3. List three different plant functions
requiring symbiotic partners.
AP Biology