Download - A directional growth movement made by a part of a stationary plant response to unilateral stimulus
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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 TropismTypes of Tropism
shoot
root
hydrotropism
no response
positive
geotropism
negative
positive
stimulus
tropism
response
watergravity unilateral lightphototropism
positive
negative
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Importance of GeotropismImportance of Geotropism
provide firm anchorage for roots
ensure the plant can get adequate supply of water & mineral salts
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To show To show Geotropism in Geotropism in
SeedlingsSeedlings
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What has happened to the radicles and plumules ?Ans: The radicles grow downwards, while the plu
mules 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 negative geotropism ?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 such geotropism ?Ans: Roots grow downwards deep into the soil to p
rovide 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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ClinostatClinostat 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 GrTo show the effect of Gravity by using a Clinostaavity by using a Clinosta
tt
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What is the purpose of marking the radicles at equal intervals ?Ans: To find out which region of the radicle grows f
aster.
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 in clinostats X and Y change ?Ans: The radicle of the seedlings in clinostat X ben
ds 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 in clinostats X and Y change ?Ans: since every side of the radicle of the seedling i
n 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 Importance of PhototropismPhototropism
enables leaves to be in a position to receive as much sunlight as possible for photosynthesis
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To show To show Phototropism in Phototropism in
ShootsShoots
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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 towar
ds 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 wit
h 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 l
ight energy for photosynthesis.
unilateral light
unilateral light
in complete darkness
A B C
light-proof box clinostat
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Importance of Importance of HydrotropismHydrotropism
ensures that a plant gets enough water 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 Experiments on Oat Coleoptileson Oat Coleoptiles
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unilaterallight
few days later
black covers
Conclusion :the tip is the place responsible for bending
Experiments Experiments on Oat Coleoptileson Oat Coleoptiles
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Experiments Experiments on Oat Coleoptileson Oat Coleoptiles
few days later
dark box
agar plate
Conclusions :the head must have produced a diffusible chemical substance which stimulates growth
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Experiments Experiments on Oat Coleoptileson Oat Coleoptiles
bending 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
micaplate
Can the explanation still work ?
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AuxinsAuxinscommonest plant hormones
regulate growth & other physiological processes in plants
produced by root tip / shoot tip they affect the elongation region of the tip
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Effect on Plant Effect on Plant PartsParts
positivegrowth
negativegrowth root
shoot
auxinconcentration
Growth ofplant
high conc. low conc. auxin concentration
plant growth
shoot
root
positive no effect
negative positive
highconc.low
conc.
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Phototropism in Phototropism in ShootShoot
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 RootGeotropism in Root The root tip produces auxins which diffuse to th
e elongation region The auxins diffuse to the lower side due to gravit
y
High auxin concentration inhibits growth in root The lower side grows slower than the upper side
The root bends downward
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