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Plant Growth & Development
Responses to Internal & External Signals
AP Biology
AP Biology
AP Biology
AP Biology
Big Ideas
 2.C.1: Organisms use feedback mechanisms to maintain their





internal environments, respond to external changes in
environment.
2.D.4: Plants, animals have chemical defenses against
infections, interruptions to homeostasis.
2.E.2: Timing, coordination of physiological events are regulated
by different mechanisms.
2.E.3: Timing, coordination of behavior are important to natural
selection.
3.D.3: Signal transduction pathways link reception with cellular
response.
4.A.3: Interactions between external stimuli, regulated gene
expression  specialization (cells, tissue, organs).
AP Biology
Big Ideas
 2.C.1: Organisms use feedback mechanisms to
maintain their internal environments, respond to
external changes in environment.
 2.D.4: Plants, animals have chemical defenses against




infections, interruptions to homeostasis.
2.E.2: Timing, coordination of physiological events are regulated
by different mechanisms.
2.E.3: Timing, coordination of behavior are important to natural
selection.
3.D.3: Signal transduction pathways link reception with cellular
response.
4.A.3: Interactions between external stimuli, regulated gene
expression  specialization (cells, tissue, organs).
AP Biology
Illustrative Examples:
 Ripening of fruit (ethylene)
AP Biology
Big Ideas
 2.C.1: Organisms use feedback mechanisms to maintain their
internal environments, respond to external changes in
environment.
 2.D.4: Plants, animals have chemical defenses
against infections, interruptions to homeostasis.
 2.E.2: Timing, coordination of physiological events are regulated
by different mechanisms.
 2.E.3: Timing, coordination of behavior are important to natural
selection.
 3.D.3: Signal transduction pathways link reception with cellular
response.
 4.A.3: Interactions between external stimuli, regulated gene
expression  specialization (cells, tissue, organs).
AP Biology
Illustrative Examples:
 Plant defenses against pathogens that
trigger infected and adjacent cells to
limit spread of infection.
AP Biology
Big Ideas
 2.C.1: Organisms use feedback mechanisms to maintain their
internal environments, respond to external changes in
environment.
 2.D.4: Plants, animals have chemical defenses against
infections, interruptions to homeostasis.
 2.E.2: Timing, coordination of physiological
events are regulated by different mechanisms.
 2.E.3: Timing, coordination of behavior are important to natural
selection.
 3.D.3: Signal transduction pathways link reception with cellular
response.
 4.A.3: Interactions between external stimuli, regulated gene
expression  specialization (cells, tissue, organs).
AP Biology
Illustrative Examples:
 Phototropism effects caused by auxin
hormone (see Figure 39.5)
AP Biology
Big Ideas
 2.C.1: Organisms use feedback mechanisms to maintain their
internal environments, respond to external changes in
environment.
 2.D.4: Plants, animals have chemical defenses against
infections, interruptions to homeostasis.
 2.E.2: Timing, coordination of physiological events are regulated
by different mechanisms.
 2.E.3: Timing, coordination of behavior are
important to natural selection.
 3.D.3: Signal transduction pathways link reception with cellular
response.
 4.A.3: Interactions between external stimuli, regulated gene
expression  specialization (cells, tissue, organs).
AP Biology
Illustrative Examples:
 Phototropism in plants lead to
maximum sunlight exposure of leaves
 differential survival rates
AP Biology
Big Ideas
 2.C.1: Organisms use feedback mechanisms to maintain their
internal environments, respond to external changes in
environment.
 2.D.4: Plants, animals have chemical defenses against
infections, interruptions to homeostasis.
 2.E.2: Timing, coordination of physiological events are regulated
by different mechanisms.
 2.E.3: Timing, coordination of behavior are important to natural
selection.
 3.D.3: Signal transduction pathways link
reception with cellular response.
 4.A.3: Interactions between external stimuli, regulated gene
expression  specialization (cells, tissue, organs).
AP Biology
Illustrative Examples:
 Phytochrome-receptor chain  “deetiolation”
AP Biology
Big Ideas
 2.C.1: Organisms use feedback mechanisms to maintain their




internal environments, respond to external changes in
environment.
2.D.4: Plants, animals have chemical defenses against
infections, interruptions to homeostasis.
2.E.2: Timing, coordination of physiological events are regulated
by different mechanisms.
2.E.3: Timing, coordination of behavior are important to natural
selection.
3.D.3: Signal transduction pathways link reception with cellular
response.
 4.A.3: Interactions between external stimuli,
regulated gene expression  specialization
(cells, tissue, organs).
AP Biology
Illustrative Examples:
 Phytochrome-receptor kinase protein
chain  “de-etiolation”




AP Biology
Stem elongation slows
Leaves expand
Roots elongate
Production of chlorophyll
Beyond the Scope of the AP Exam…



(2.C.2) No specific behavioral/physical
mechanisms required
(2.E.1) Names of specific stages in embryonic
development are required
(2.E.2) Memorization of names, molecular
structures and specific effects of all plant
hormones
AP Biology
© 2011 Pearson Education, Inc.
Environmental Influences
o Atmosphere:
•
•
•
•
Humidity
Air temperature
Wind
Radiation
o Plant Regulation:
•
•
•
•
Stomatal Opening
Leaf temperature
Leaf loss
Root development
o Soil Supply:
•
•
•
•
Soil moisture
Soil texture, density
Soil temperature
Soil depth
AP Biology
Distinction
Growth
 Increase in number, size,

and/or volume of cells in
multicellular organisms
Quantitative in nature
AP Biology
Development
 The emergence of

specialized,
morphologically different
body parts.
Qualitative in nature
Key Points
1) Plants develop via unique combinations of genes,
hormones, and the environment.
2) Five plant hormones cause different kinds of growth
and development.
3) Plants adjust their growth in response to
environmental stimuli.
4) Like other organisms, plants operate according to
“biological clocks”.
5) Plant life cycles are influenced by complicated
environmental and hormonal cues.
AP Biology
Basic Mechanism of Hormone Action
1. Reception: Signal (typically hormone) is received by
cell
2. Transduction: Often complex series of intermediate
steps linking reception and response.
3. Response: how the cell makes sense of input (on,
off, or limiting/potentiating activity
AP Biology
 http://www.wiley.com/college/boyer/047
0003790/animations/signal_transductio
n/signal_transduction.htm
 http://www.hartnell.edu/tutorials/biolog
y/signaltransduction.html
 http://www.youtube.com/watch?v=qOV
kedxDqQo&list=PLFCE4D99C4124A27A
&index=47
AP Biology
Action of Hormones
 In general hormones control plant
development by:
Division of cells
 Elongation
 Differentiation of cells
 Physiological response to
environmental for short term periods
(stomatal opening)

AP Biology
Action of Hormones
 They do this by regulating:
gene expression (transcriptional control)
 activity of enzymes (post-transcriptional control)
 changing membrane properties

 e.g. sterols: increasing fluidity
AP Biology
Growth in Animals
 Animals grow throughout the whole
organism

AP Biology
many regions & tissues at different rates
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
AP Biology
AP Biology
AP Biology
Key Points
1) Plants develop via unique combinations of genes,
hormones, and the environment.
2) Five plant hormones cause different kinds of
growth and development.
3) Plants adjust their growth in response to
environmental stimuli.
4) Like other organisms, plants operate according to
“biological clocks”.
5) Plant life cycles are influenced by complicated
environmental and hormonal cues.
AP Biology
Plant Hormone
Location
Functions
Promotes stem
elongation; ends
dormancy of seeds, buds
Gibberellins
Apical meristems of buds,
roots, leaves, embryos
Auxins
Bud, leaf apical meristems &
embryos
Cytokinins
Made in roots, travels
elsewhere
Promote cell division, leaf
expansion; retards leaf
aging
Abscisic Acid
Leaves, stems, & unripened
fruit
Promotes stomatal
closure, bud and seed
dormancy
Ethylene
Notable amounts in seeds,
fruits, stems, leaves, and
roots
Promotes ripening of fruit,
abscission of leaves,
flowers, fruits, roots
AP Biology
Promote cell elongation;
role in photo/gravitropism
G
G
G
G
AP Biology
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
Plant Hormone
Location
Functions
Promotes stem
elongation; ends
dormancy of seeds, buds
Gibberellins
Apical meristems of buds,
roots, leaves, embryos
Auxins
Bud, leaf apical meristems &
embryos
Cytokinins
Made in roots, travels
elsewhere
Promote cell division, leaf
expansion; retards leaf
aging
Abscisic Acid
Leaves, stems, & unripened
fruit
Promotes stomatal
closure, bud and seed
dormancy
Ethylene
Notable amounts in seeds,
fruits, stems, leaves, and
roots
Promotes ripening of fruit,
abscission of leaves,
flowers, fruits, roots
AP Biology
Promote cell elongation;
role in photo/gravitropism
G
A
A
G
G A
G
AP Biology
Auxin
 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
Plant Hormone
Location
Functions
Ptomotes stem
elongation; ends
dormancy of seeds, buds
Gibberellins
Apical meristems of buds,
roots, leaves, embryos
Auxins
Bud, leaf apical meristems &
embryos
Cytokinins
Made in roots, travels
elsewhere
Promote cell division,
leaf expansion; retards
leaf aging
Abscisic Acid
Leaves, stems, & unripened
fruit
Promotes stomatal
closure, bud and seed
dormancy
Ethylene
Notable amounts in seeds,
fruits, stems, leaves, and
roots
Promotes ripening of fruit,
abscission of leaves,
flowers, fruits, roots
AP Biology
Promote cell elongation;
role in photo/gravitropism
G
A
A
G
G A
C
AP Biology
G
Cytokinins
 Effects
Stimulates cell division
 Used to prolong shelf life of cut flowers,
other fruits & veggies
 Most abundant in root, shoot meristems

AP Biology
Plant Hormone
Location
Functions
Ptomotes stem
elongation; ends
dormancy of seeds, buds
Gibberellins
Apical meristems of buds,
roots, leaves, embryos
Auxins
Bud, leaf apical meristems &
embryos
Cytokinins
Made in roots, travels
elsewhere
Promote cell division, leaf
expansion; retards leaf
aging
Abscisic Acid
Leaves, stems, & unripened
fruit
Promotes stomatal
closure, bud and seed
dormancy
Ethylene
Notable amounts in seeds,
fruits, stems, leaves, and
roots
Promotes ripening of fruit,
abscission of leaves,
flowers, fruits, roots
AP Biology
Promote cell elongation;
role in photo/gravitropism
G
A
AA
A
G
AA
C
G A
G
AA
AP Biology
Abscisic acid
 Effects
slows growth
 seed dormancy

 high concentrations of abscisic acid
 germination only after it is inactivated or leeched
out
 survival value:
seed will germinate only
under optimal conditions
 light, temperature, moisture
AP Biology
Plant Hormone
Location
Functions
Ptomotes stem
elongation; ends
dormancy of seeds, buds
Gibberellins
Apical meristems of buds,
roots, leaves, embryos
Auxins
Bud, leaf apical meristems &
embryos
Cytokinins
Made in roots, travels
elsewhere
Promote cell division, leaf
expansion; retards leaf
aging
Abscisic Acid
Leaves, stems, & unripened
fruit
Promotes stomatal
closure, bud and seed
dormancy
Ethylene
Notable amounts in seeds,
fruits, stems, leaves, and
roots
Promotes ripening of fruit,
abscission of leaves,
flowers, fruits, roots
AP Biology
Promote cell elongation;
role in photo/gravitropism
G
A
AA
E
A
E
G
AA
G A
E
C
G
AA
AP Biology
E
Big Ideas
 2.C.2) Organisms respond to changes in their
external environments.
Illustrative Examples:
•Ripening of Fruit (ethylene)
AP Biology
© 2011 Pearson Education, Inc.
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
AP Biology
Key Points
1) Plants develop via unique combinations of genes,
hormones, and the environment.
2) Five plant hormones cause different kinds of growth
and development.
3) Plants adjust their growth in response to
environmental stimuli.
4) Like other organisms, plants operate according to
“biological clocks”.
5) Plant life cycles are influenced by complicated
environmental and hormonal cues.
AP Biology
Mix & Match Review: Ch. 39.3-5
1. Phytochromes
2. Circadian rhythms
3. Tropisms (3 kinds)
1, 4, 7
1. Environmental factors
affecting plants (list,
describe at least five)
2, 5, 8
AP Biology
© 2011 Pearson Education, Inc.
3, 6
1. Plant defenses (list, describe at
least five)
Hormones and Plant Tropisms:
 Plant tropism: when a root or a shoot turns toward

or away from a stimulus, caused by hormone
mediated shifts in the rates at which different cells
grow and elongate.
Plant tropisms include:
1.
2.
3.
Gravitropism (growth away from/toward gravity)
Phototropism (growth toward light)
Thigmotropism (growth away from mechanical pressure)
AP Biology
Adjustment in the Rate and Direction
of Growth
 Gravitropism

Response to gravity
 Root curves down (+ gravitropism)
 Shoot curves up (- gravitropism)
AP Biology
Adjustment in the Rate and Direction
of Growth
 Gravitropism

Response to gravity
 Root curves down (+ gravitropism)
 Shoot curves up (- gravitropism)
 Hormone responsible: AUXIN

Auxin causes cell elongation

Auxin is inhibitory in high concentrations in root
tissue
AP Biology
Adjustment in the Rate and Direction
of Growth
 Gravitropism

Response to gravity
 Root curves down (+ gravitropism)
 Shoot curves up (- gravitropism)
 Hormone responsible: AUXIN

Auxin causes cell elongation

Auxin is inhibitory in high concentrations in root
tissue
 Statoliths are involved in root response

They are clusters of unbound starch grains in plastids

They settle to the bottoms of root cells and
redistribute auxin
AP Biology
Gravitropism:
Shoot Mechanism
CELL
AP Biology
Effect as
soon as
30 min
High auxin = high
elongation
Gravitropism Root Mechanism:
 Root:
Cells elongate
HOW???
1. Statoliths settle
to bottom of
root cells.
2. Auxins are
pushed out of
root tip.
3. High [AUX] =
elongation
inhibited.
AP Biology
Cells here
inhibited from
elongation
4. Curves down.
Adjustment in the Rate
and Direction of Growth
o Phototropism
o Response to light
o Whenever stems or leaves adjust the rate and direction of
their growth in response to light
o Hormone responsible: AUXIN
o Auxin causes cell elongation
o Mechanism:
o Auxin moves from the tip of the shoot into cells less
exposed to light.
o The cells on the side away from the light elongate and
cause the stem to bend toward the light.
AP Biology
Phototropism in Coleoptile
AP Biology
tp://sunflower.bio.indiana.edu/~rhangart/plantmotion/movements/tropism/tropisms.h
Adjustment in the Rate
and Direction of Growth
• Thigmotropism: SLOW RESPONSE
• Response to contact with solid objects
• Whenever stems or leaves adjust the rate and direction of
their growth in response to contact with another object
• Hormones responsible: AUXIN and ETHYLENE
• Auxin causes cell elongation
• Mechanism
• Auxin moves into cells away from the contact point.
• The cells on the side away from the contact elongate and
cause the tendril or vine to coil.
AP Biology
Adjustment in the Rate
and Direction of Growth
Fig. 32.11, p. 551
Elongation
on this side
AP Biology
Tree
Sensitive Mimosa
After Contact
Before Contact
AP Biology
Key Points
1) Plants develop via unique combinations of genes,
hormones, and the environment.
2) Five plant hormones cause different kinds of growth
and development.
3) Plants adjust their growth in response to
environmental stimuli.
4) Like other organisms, plants operate according
to “biological clocks”.
5) Plant life cycles are influenced by complicated
environmental and hormonal cues.
AP Biology
Big Ideas
 2.E.3) Timing and coordination of behavior are
regulated by various mechanisms and are
important in natural selction.
Illustrative Examples:
•Biology of Pollination
AP Biology
© 2011 Pearson Education, Inc.
Big Ideas
 2.E.2) Timing and coordination of physiological
events are regulated by multiple mechanisms.
Illustrative Examples:
•Circadian rhythms/24-hour clock
AP Biology
© 2011 Pearson Education, Inc.
Mechanism for Timing & Controlling Events
 Biological Clock (B.C.):


internal timing mechanism that sets the time for
recurring changes in biochemical events
daily and seasonal adjustments in patterns of
growth, development and reproduction
 Circadian rhythm (subset of B.C.s):


A biological activity that recurs in cycles of about 24
hours (21-27 is typical); act independent of stimuli
These rhythms are controlled by biological clocks
 Examples: sleep-wake cycles, active-inactive periods,
rhythmic leaf shifts
AP Biology
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1 A.M.
6 A.M.
NOON
3 P.M.
10 P.M.
MIDNIGHT
Refer to Fig. 39.20
Big Ideas
 2.C.2) Organisms respond to changes in their
external environments.
Illustrative Examples:
•Phototropism & photoperiodism in plants
AP Biology
© 2011 Pearson Education, Inc.
Photoperiodism:
 Chromophore: changes from one isomeric
form to another and this activates or
inactivates the phytochrome molecule.
Common at dawn
Common at dusk
AP Biology
Page 552
Flowering - A Case of
Photoperiodism
 Short-day plants: flower in
late summer, early fall

Ex.: strawberry, poinsettias
 Long-day plants: flower in
the spring

Ex.: petunia, iris, potato
 Day-neutral plants: flower
when mature

Ex.: tomatoes, rice, rose
AP Biology
Photoperiodism and Flowering:
 Advantages:

Day/night length less variable than
temperature and therefore a better judge of
seasonality

Increases reproductive efficiency
 Coordination and balance with pollinators
AP Biology
Concept 39.3: Responses to light are critical for plant success
 Light cues many key events in plant growth and

development
Effects of light on plant morphology are called
photomorphogenesis
AP Biology
© 2011 Pearson Education, Inc.
Fig. 39.16
Phototropic effectiveness
Figure 39.16
1.0
436 nm
0.8
0.6
0.4
0.2
0
400
450
500
550
600
650
700
Wavelength (nm)
(a) Phototropism action spectrum
Light
Time  0 min
Time  90 min
AP Biology
(b) Coleoptiles before and after light exposures
Phototropic effectiveness
Figure 39.16a
1.0
436 nm
0.8
0.6
0.4
0.2
0
400
450
500
550
600
Wavelength (nm)
(a) Phototropism action spectrum
AP Biology
650
700
Figure 39.16b
Light
Time  0 min
Time  90 min
(b) Coleoptiles before and after light exposures
AP Biology
 Different plant responses can be mediated by

the same or different photoreceptors
There are two major classes of light receptors:


blue-light photoreceptors
phytochromes
AP Biology
© 2011 Pearson Education, Inc.
Phytochromes as Photoreceptors
 Phytochromes are pigments that regulate many

of a plant’s responses to light throughout its life
These responses include:
seed germination
 shade avoidance

AP Biology
© 2011 Pearson Education, Inc.
Figure 39.17
Fig. 39.17
RESULTS
Red
Dark
Red Far-red
Dark
Dark (control)
Red Far-red Red
AP Biology
Dark
Red Far-red Red Far-red
Figure 39.17a
Dark (control)
AP Biology
Figure 39.17b
Red
AP Biology
Dark
Figure 39.17c
Red Far-red
AP Biology
Dark
Figure 39.17d
Red Far-red Red
AP Biology
Dark
Figure 39.17e
Red Far-red Red Far-red
AP Biology
 Red light increased (+) germination
 Far-red light inhibited (-) germination
 The photoreceptor responsible for the opposing
effects of red and far-red light is a phytochrome
AP Biology
© 2011 Pearson Education, Inc.
Figure 39.18
Two identical subunits
Chromophore
Photoreceptor activity
Kinase activity
AP Biology
Figure 39.19
Pr
Red light
Synthesis
Far-red
light
Slow conversion
in darkness
(some plants)
AP Biology
Pfr
Responses:
seed
germination,
control of
flowering, etc.
Enzymatic
destruction
Biological Clocks and Circadian
Rhythms
 Many plant processes oscillate during
the day
 Many legumes lower their leaves in the
evening and raise them in the morning,
even when kept under constant light or
dark conditions
AP Biology
© 2011 Pearson Education, Inc.
Key Points
1) Plants develop via unique combinations of genes,
hormones, and the environment.
2) Five plant hormones cause different kinds of growth
and development.
3) Plants adjust their growth in response to
environmental stimuli.
4) Like other organisms, plants operate according to
“biological clocks”.
5) Plant life cycles are influenced by complicated
environmental and hormonal cues.
AP Biology
Big Ideas
 2.D.4) Plants and animals have a variety of
chemical defenses against infections that affect
dynamic homeostasis.
Illustrative Examples:
•Plant defenses against pathogens (see Fig. 39.28)
AP Biology
© 2011 Pearson Education, Inc.
AP Biology
AP Biology