Transcript
8/4/2019 Growth Response in Plants
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A directional growth movement
made by a part of a stationary
plant response to unilateral
stimulus
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Types of Tropism
shoot
root
hydrotropism
no response
positive
geotropism
negative
positive
stimulus
tropism
response
watergravity unilateral light
phototropism
positive
negative
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Importance of Geotropism
provide firm anchorage for roots ensure the plant can get
adequate supply of water &
mineral salts
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To show Geotropism
in Seedlings
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What has happened to the radicles and plumules ?Ans: The radicles grow downwards, while the plumules
grow upwards.
in complete darkness in complete darkness
P
Q R
P
Q R
plumule radicle
after 2 days
(a) Beginning of experiment (b) End of experiment
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Why is it necessary to leave the apparatus in darkness ?
Ans: To avoid any stimulus from light.
in complete darkness in complete darkness
P
Q R
P
Q R
plumule radicle
after 2 days
(a) Beginning of experiment (b) End of experiment
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Do the radicles show positive geotropism or negativegeotropism ?
Ans: Positive geotropism.
in complete darkness in complete darkness
P
Q R
P
Q R
plumule radicle
after 2 days
(a) Beginning of experiment (b) End of experiment
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What advantage do the seedlings have by showing suchgeotropism ?
Ans: Roots grow downwards deep into the soil to provide
a firm anchorage underground and absorb water and
mineral salts in the soil.
in complete darkness in complete darkness
P
Q R
P
Q R
plumule radicle
after 2 days
(a) Beginning of experiment (b) End of experiment
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Clinostat
for control experiments
contains a cork disc which can be set to rotate
in a vertical or horizontal plane by a motor to make factors uniform (evenly distributed)
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To show the effect of
Gravity by using a Clinostat
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What is the purpose of marking the radicles at equalintervals ?
Ans: To find out which region of the radicle grows faster.
plastic cover lined with
moist blotting paper
X
Y
in complete
darkness
seedling in X
seedling in Y
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Does the direction of growth of the seedlings inclinostats X and Y change ?
Ans: The radicle of the seedlings in clinostat X bends
downwards in response to the pull of gravity
plastic cover lined with
moist blotting paper
X
Y
in complete
darkness
seedling in X
seedling in Y
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Does the direction of growth of the seedlings inclinostats X and Y change ?
Ans: since every side of the radicle of the seedling in
clinostat Y is acted on by gravity, the radicle will
grow straight horizontally.
plastic cover lined with
moist blotting paper
X
Y
in complete
darkness
seedling in X
seedling in Y
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What is the purpose of setting up clinostat Y ?Ans: Serve as a control for comparison.
plastic cover lined with
moist blotting paper
X
Y
in complete
darkness
seedling in X
seedling in Y
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Importance of Phototropism
enables leaves to be in a positionto receive as much sunlight as
possible for photosynthesis
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To show Phototropism
in Shoots
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What has happened to the shoots of plants A, B and C ?
Ans: The shoots in pot A respond by growing towards the
light source. The shoot in pot B do not show any
curvature but grow vertically upwards...
unilateral
light
unilateral
light
in complete darkness
A B C
light-proof
box clinostat
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What has happened to the shoots of plants A, B and C ?
Ans: the shoots in pot C grow vertically upwards with
slender and longer nodes, and carries smaller leaves
which are yellow in colour.
unilateral
light
unilateral
light
in complete darkness
A B C
light-proof
box clinostat
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What is the effect of the clinostat on the shoot of plant B ?
Ans: The revolving clinostat cancel out the effect of
unilateral light on the shoot of plant B.
unilateral
light
unilateral
light
in complete darkness
A B C
light-proof
box clinostat
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What is the significance of phototropism to plants ?
Ans: This tropism ensures that a plant gets enough light
energy for photosynthesis.
unilateral
light
unilateral
light
in complete darkness
A B C
light-proof
box clinostat
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Importance of Hydrotropism
ensures that a plant gets enoughwater as a raw material for
photosynthesis & enough mineral
salts to maintain normal growth
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no growth grows
dark box
few days later
Conclusions :
The tip is responsible for growth
cut & replaced tip
decapitated
Experiments
on Oat Coleoptiles
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unilateral
light
few days later
black covers
Conclusion :
the tip is the place responsible for bending
Experiments
on Oat Coleoptiles
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Experiments
on Oat Coleoptiles
fewdayslater
dark box
agar plate
Conclusions :
the head must have produced a diffusible
chemical substance which stimulates growth
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Experiments
on Oat Coleoptilesbending directions
Explanation of results :
The side with the tip has a higher concentration of that particular
chemical, the growth rate is faster than the other side
the tip is put aside
bending directions
mica
plate
Can the explanation still work ?
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Auxins
commonest plant hormones
regulate growth & other physiologicalprocesses in plants
produced by root tip / shoot tip
they affect the elongation region of the
tip
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Effect on Plant Parts
positivegrowth
negative
growth root
shoot
auxin
concentration
Growth of
plant
high conc. low conc.
auxin concentrationplant growth
shoot
root
positive no effect
negative positive
high
conc.low
conc.
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Phototropism in Shoot
The shoot tip produces auxins which diffuse downward
The auxins diffuse to the shaded side due to the presence
of unilateral light
High auxin concentration
stimulates growth in shoot
The shaded side grows faster
than the lighted side
The shoot bends towards the light
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Geotropism in Root The root tip produces auxins which diffuse to the
elongation region
The auxins diffuse to the lower side due to gravity
High auxin concentration inhibits growth in root
The lower side grows slower than the upper side
The root bends downward
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~END~
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