Transcript Plant Hormones

TROPISM
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TROPISM
Plant growth in response to a
stimulus
(“tropo” – ”turn”)
There are many types of tropisms :
• Phototropism
• Geotropism
3 main types
•Thigmotropism
• Hydrotropism
• Chemotropism
• Thermotropism
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TROPISM
Plant growth in response to a
stimulus
(“tropo” – ”turn”)
There are many types of tropisms :
• Phototropism – growth in response to light
• Geotropism – growth in response to gravity
•Thigmotropism – growth in response to touch
• Hydrotropism – growth in response to water
*Can be positive
• Chemotropism – growth in response to chemical (towards stimulus)
or negative (away
stimuli
from stimulus)
• Thermotropism – growth in response to heat
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PHOTOTROPISM
(“Photo” – light)
The growth response of a plant in
response to light direction is
called phototropism.
Ex. Stems growing toward the window to get to
the light
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Why is phototropism important to a plant?
IMPORTANCE OF
PHOTOTROPISM
Enables leaves to be in the best
position possible to receive adequate
light for photosynthesis
http://www.darienps.org/teachers/otterspoor/botany/tropisms/Gra
vitropismwlight.jpg
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GEOTROPISM
(“Geo” – Earth)
Geotropism is the growth
of a plant in response to
gravity.
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What is positive and negative geotropism?
Positive Geotropism
Negative Geotropism
It is the growth of a plant towards
the center of the earth-down with
gravity.
Ex. roots growing down
Negative Geotropism
It is the growth of a plant
away from the center of the
earth-opposite from the pull of
gravity
Ex. stems grow up
Positive Geotropism
Why is geotropism important to a plant?
IMPORTANCE OF
GEOTROPISM
• Pulls roots down to anchor a plant
• Roots can get needed water and
minerals if they stay in the soil
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THIGMOTROPISM
(“Thigmo” – “touch”)
Thigmotropism is the growth
of a plant in response to
touch/contact.
Photo by Christopher Meloche
Tendrils on a sweet pea
Vines growing on a wall or fence
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SOME OTHER
TYPES OF
TROPISM
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THERMOTROPISM
(“Therm” – “heat”)
Thermotropism is the tendency of plants or other
organisms to bend toward or away from heat.
HYDROTROPISM
(“hydro” – “water”)
Ex. curling of Rhododendron leaves in Hydrotropism is the growth in response
to water. Ex. roots growing toward
response to cold temperatures.
moisture
Chemotropism
(“Chemo” – chemical”)
Chemotropism is movement caused by
chemical stimuli. Ex. Growth of a pollen tube is
always towards the ovules
so that reproduction can occur
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Photo/Geotropism:
http://plantsinmotion.bio.indiana.ed
u/plantmotion/movements/tropism/t
ropisms.html
Thigmotropism http://www.youtube.com/watch?v=
yMHmU3eZsYk
Corn plant growing:
http://www.youtube.com/watch?v=iFCdAg
eMGOA&feature=related
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Hormone = Gr. “to excite”
1) active in small amounts
2) produced in one part of plant &
transported to another for action
3) action is specific for that site
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Depending on site of action
Developmental stage of plant
Concentration of hormone
◦ stimulate growth but too much inhibits
growth
◦ functions:
◦ 1) root initiation, stem elongation
◦ 2) retard abscission (loss) of leaves &
fruits.
◦ 3) stimulates cell differentiation
◦ 4) apical dominance
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discovered due to a fungus Giberella
which causes Japanese “foolish” rice
seedling disease
induces flowering
stimulates growth by increasing cell
size & numbers.
Seedless grapes are usually smaller than seeded grapes because the
developing seeds produce another hormone, gibberellin, that promotes the
fruits increase in size and sugar content. By spraying seedless grapes with
gibberellins artificially, the farmer can produce large, marketable grapes.
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1) induces cell division (cytokinesis)
2) affects root growth & differentiation
3) stimulates germination
4) delays senescence (aging); the
progression of irreversible change that
eventually leads to death
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1) stimulates abscission
2) converts vegetative buds
(active) to dormant buds
3) inhibits growth
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1) promotes fruit ripening
2) stimulates production of
cellulase
1. Tropism is a growth or turning movement of a plant in response
to –
a) A response
b) A stimulus
c) A reaction
d) An effect
2. Which of the following tropisms is the same as geotropism?
a. thigmotropism
b. hydrotropism
c. phototropism
d. gravitropism
3. What benefit does positive geotropism provide for a growing
plant?
4) Removal of the tip of a plant stimulates
lateral growth AND the plant gets bushier,
because the tip of a stem produces:
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A)
auxins
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B)
cytokinins
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C)
gibberellins
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D)
ethylene
5) Ripening of fruits, such as bananas, is hastened (sped up) by
A)
B)
C)
D)
abiscisic acid
cytokinin
indoleacetic acid
ethylene
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Today we will be studying the effects of
tropism on germinated cucumber seeds.
Materials needed
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Petri Dish
Marker
3 seedlings
Cotton
Water
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Make sure the cotton is fluffy.
Take a photo of the prepared dish, then seal
the petri dish around the perimeter.
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Shoot
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Root
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Hypothesis – Will tropism have an effect on
the growth of the seedlings? If so which types
of tropism will be displayed? Will they be
positive or negative?
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Lab Report
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1 -2 Pages
Introduction
Materials
Procedure
Results (Data)
Conclusion
http://www.biologycorner.com/worksheets/labrepo
rt.html