Transcript Plant Growth and Transport

Plant Growth
AP Biology
2007-2008
Growth in Animals
 Animals grow throughout the whole
organism

many regions & tissues at different rates
 versus…
AP Biology
Growth in Plants
 Specific regions of growth: meristems
stem cells: perpetually embryonic tissue
 regenerate new cells

 apical shoot meristem
 growth in length
 primary growth
 apical root meristem
 growth in length
 primary growth
 lateral meristem
 growth in girth
 secondary growth
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2-year old stem
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Apical meristems
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shoot
root
Root structure & growth
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protecting the meristem
Shoot growth
 Apical bud & primary
growth of shoot
region of stem growth
 axillary buds

 “waiting in the wings”
protecting the meristem
Young leaf
primordium
Apical meristem
Older leaf
primordium
Lateral bud
primordium
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Vascular tissue
Primary
xylem
Growth in woody plants
Primary
phloem
 Woody plants grow in
Epidermis
height from tip


Lateral
meristems
primary growth
apical meristem
 Woody plants grow in
diameter from sides


secondary growth
lateral meristems
Primary
phloem
Secondary
phloem
Secondary
Primary xylem
xylem
 vascular cambium
 makes 2° phloem & 2° xylem
 cork cambium
 makes bark
Annual
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growth
layers
Bark
Secondary growth
 Secondary growth

growth in diameter
 thickens & strengthens older part of tree

cork cambium makes bark
 growing ring around tree

vascular cambium makes xylem & phloem
 growing ring around tree
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Vascular cambium division…
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Vascular cambium
Why are early
& late growth
different?
 Phloem produced to the outside
 Xylem produced to the inside
bark
cork
cambium
phloem
xylem
vascular
cambium
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late
early
last year’s xylem
cork cambium
Woody stem
How old is
this tree?
vascular cambium
late
early
3
2
1
xylem
phloem
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bark
Tree trunk anatomy
tree girdling
What does girdling
do
to a tree?
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Aaaargh!
Murderer!
Arborcide!
Where will the carving be in 50 years?
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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
Water & mineral absorption
 Water absorption from soil
osmosis
 aquaporins

 Mineral absorption
active transport
 proton pumps

 active transport of
H+
aquaporin
root hair
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proton
pumps
H2O
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!
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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
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
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On a plant…
What’s a source…What’s a sink?
can flow
1m/hr