Plant Anatomy
AP Biology
2006-2007
Basic plant anatomy
 root


root tip
root hairs
 shoot (stem)

nodes
 internodes

buds
 terminal or apical buds
 axillary buds
 flower buds & flowers
 leaves


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mesophyll tissue
veins (vascular bundles)
Meristem
 Regions of growth
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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Apical meristems
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shoot
root
Leaves
 Function of leaves

photosynthesis
 energy production
 CHO production
gas exchange
 transpiration

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Modified leaves
tendrils (peas)
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succulent leaves
spines (cacti)
colored leaves (poinsetta)
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Interdependent systems
 Both systems
depend on the
other
roots depend on
sugars produced
by photosynthetic
leaves
 shoots depend on
water & minerals
absorbed from the
soil by roots

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sugars
water &
minerals
Plant TISSUES
 Dermal


epidermis (“skin” of plant)
single layer of tightly
packed cells that covers
& protects plant
 Ground


bulk of plant tissue
photosynthetic mesophyll,
storage
 Vascular


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transport system in
shoots & roots
xylem & phloem
vessel elements
 Xylem

vessel
element

Vascular tissue
move water & minerals up from roots
dead cells at functional maturity
 only cell walls remain
 need empty pipes to efficiently move H2O
 transpirational pull
dead cells
Aaaah…
Structure–Function
again!
tracheids
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Phloem: food-conducting cells
 carry sugars & nutrients throughout plant
sieve tube
companion cell
sieve plate
plasmodesmata
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living cells
Putting it all together
 Obtaining raw materials

sunlight
 leaves = solar collectors

CO2
 stomates = gas exchange

H2O
 uptake from roots

nutrients
 uptake from roots
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
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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
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
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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
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
Plant Reproduction
In a nutshell
AP Biology
2007-2008
Plant Diversity
mosses
ferns
conifers
flowering plants
Bryophytes
Pteridophytes
Gymnosperm
Angiosperm
non-vascular
land plants
seedless
vascular plants
pollen &
“naked” seeds
flowers & fruit
flowers & fruits
pollen & seeds
vascular system
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common ancestor
xylem cells
tracheids
Animal vs. Plant life cycle
Animal
Plant
diploid
multicellular
individual
2n
mitosis
meiosis
fertilization
haploid
unicellular
gametes
1n
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diploid
multicellular
sporophyte
2n
mitosis
fertilization
meiosis
gametes
1n
spores
1n
mitosis
mitosis
haploid
multicellular
gametophyte
1n
alternation of generations
Bryophytes
 Mosses & liverworts





non-vascular
diploid
swimming sperm
multicellular
dominant haploid gametophyte
sporophyte
dependent sporophyte
2n
mitosis
spores for reproduction
meiosis
fertilization
gametes
1n
spores
1n
mitosis
mitosis
haploid
multicellular
gametophyte
1n
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alternation
of generations
Pteridophytes
 Ferns




vascular
swimming sperm
dominant sporophyte
independent gametophyte
 fragile

diploid
multicellular
sporophyte
2n
mitosis
fertilization
meiosis
gametes
1n
spores
1n
mitosis
mitosis
spores for reproduction
haploid
archegonia
antheridia
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alternation
of generations
haploid
multicellular
gametophyte
1n
Gymnosperm
 Conifers





vascular
diploid
pollen (sperm)
multicellular
dominant sporophyte
sporophyte
dependent reduced gametophyte
2n
mitosis
cones, seeds for reproduction fertilization
meiosis
female
male
AP Biology
gametes
1n
spores
1n
mitosis
mitosis
haploid
multicellular
gametophyte
1n
Angiosperm
 Flowering plants





vascular
diploid
pollen (sperm)
multicellular
dominant sporophyte
sporophyte
dependent reduced gametophyte
2n
mitosis
flowers, fruits, seeds for
meiosis
fertilization
reproduction
male
gametophyte
in pollen
(haploid)
female
gametophyte
in ovary
(haploid)
AP Biology
gametes
1n
spores
1n
mitosis
mitosis
haploid
multicellular
gametophyte
1n
Angiosperm: flowering plants
AP Biology
polar
nuclei
Angiosperm life cycle
male
gametophyte
in pollen
(haploid)
pollen
grains
egg
cell
fertilization
female
gametophyte
in ovary
(haploid)
AP Biology
sporophyte
in seed
(diploid)
Seed dispersal
 Plants produce enormous numbers of seeds to compensate
for low survival rate


vast amount of genetic variation for natural selection to screen
Seed Aviation
r-strategy
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K-strategy
Plant Responses to
Stimuli
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Plant hormones
 auxin
 gibberellins
 abscisic acid
 ethylene
 and more…
AP Biology
Auxin (IAA)
 Effects
controls cell division
& differentiation
 phototropism

 growth towards light
 asymmetrical distribution of auxin
 cells on darker side elongate faster
than cells on brighter side

AP Biology
apical dominance
Gibberellins
 Family of hormones

over 100 different gibberellins identified
 Effects
stem elongation
 fruit growth
 seed germination

AP Biology
plump grapes in grocery
stores have been treated
with gibberellin hormones
while on the vine
Abscisic acid (ABA)
 Effects
slows growth
 seed dormancy

 high concentrations of abscisic acid
 germination only after ABA is inactivated or
leeched out
 survival value:
seed will germinate only
under optimal conditions
 light, temperature, moisture
AP Biology
Ethylene
 Hormone gas released by plant cells
 Effects
fruit ripening
 leaf drop

 like in Autumn
 apoptosis
One bad apple
spoils the
whole bunch…
AP Biology
Fruit ripening
 Adaptation


hard, tart fruit protects
developing seed from herbivores
ripe, sweet, soft fruit attracts
animals to disperse seed
 Mechanism

triggers ripening process
 breakdown of cell wall
 softening
 conversion of starch to sugar
 sweetening

positive feedback system
 ethylene triggers ripening
 ripening stimulates more ethylene production
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Other Responses
 Gravitropism

AP Biology
Occurs as soon as seed germinates,
ensures root grows into soil and shoot
grows toward sunlight. (Auxin)
Other Responses
 Thigmotropism

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Response to touch, allows the plant to
use mechanical supports as it grows,
also can result in rapid leaf movements
(similar to action potentials in nerves)
Other Responses
 Photoperiodism
A physical response, such as flowering
to the photoperiod
 Actually controlled by night length not
day length
 Long-day plants flower in late spring or
early summer
 Short-day plants flower in late summer
fall or winter

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Other Responses
 Photoperiodism
AP Biology