THE TYPES OF MOVEMENT
OBSERVED IN PLANTS
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A directional growth movement made by a part of a stationary plant
response to unilateral stimulus. The dictionary defines tropism as an
orientation of an organism to an external stimuli.
There are numerous types of tropisms :
• Hydrotropism
(These are the 3 main types of
• Phototropism
tropism and these would
• Geotropism
broadly discussed accordingly.)
• Chemotropism
• Thigmotropism
• Heliotropism
• Thermotropism
• And many more………..
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Stimulus
Tropism
Response
Gravity
Unilateral light
Geotropism Phototropism
Water
Hydrotropism
Shoot
Negative
Positive
No response
Root
Positive
Negative
Positive
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GEOTROPISM
Geotropism is the growth of a living organism in response to gravity.
There are two types of geotropisms. They are:
1. Positive geotropism
2. Negative geotropism
Negative Geotropism
Positive Geotropism
It is the growth of an organism (i.e.
plants) towards the centre of the
earth.
Negative Geotropism
It is the growth of an organism
away from the centre of the
earth.
An example of geotropism is
given in the picture.
Positive Geotropism
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IMPORTANCE OF
GEOTROPISM
Provides firm anchorage for roots.
Ensure the plant can get adequate
supply of water & mineral salts.
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PHOTOTROPISM
The growth response of a living organism on
response to light direction is called
phototropism. Like geotropism even
phototropism is of 2 types: 1. Positive
Positive
Phototropism
2. Negative
In positive phototropism living
organism grow towards the light. For
example- Stems are positively
phototrophic.
Negative
Phototropism
In negative phototropism living organisms
grow away from the light. For example- Roots
are negatively phototrophic.
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IMPORTANCE OF PHOTOTROPISM
Phototropism enables leaves to be in a
position to receive as much sunlight as possible
for photosynthesis.
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HYDROTROPISM
Hydrotropism is the growth of a living organism
in response to water. Hydrotropism is the
directed growth of the root in relation to the
gradient in moisture. It begins in the root cap
with the sensing of moisture.
Growing away from water
(Negative Hydrotropism)
Both positive and negative
hydrotropism exist in living
organisms and its direction of
growth depends upon a stimulus or
gradient in water concentration.
Growing towards water (Positive
Hydrotropism)
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IMPORTANCE OF HYDROTROPISM
Ensures
that a plant gets enough water
as a raw material for photosynthesis &
enough mineral salts to maintain normal
growth
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Experiment Number 1
To show Geotropism in Seedlings
Let’s start the experiment
In complete darkness
Plumule
Radicle
After 2 days
P
Q
In complete darkness
R
(a) Beginning of experiment
P
Q
R
(b) End of experiment
Why is it necessary to leave the apparatus in darkness ?
Answer: To avoid any stimulus from light.
In complete darkness
Plumule
Radicle
After 2 days
P
Q
In complete darkness
R
(a) Beginning of experiment
P
Q
R
(b) End of experiment
Do the radicles show positive geotropism or negative
geotropism?
Answer: Positive geotropism.
In complete darkness
Plumule
Radicle
After 2 days
P
Q
In complete darkness
R
(a) Beginning of experiment
P
Q
R
(b) End of experiment
What advantage do the seedlings have by showing
such geotropism ?
Answer: Roots grow downwards deep into the soil to
provide a firm anchorage underground and absorb
water and mineral salts in the soil.
Want to know what a clinostat is ? CLICK HERE
EXPERIMENT
NUMBER 2
To show the effect of Gravity by
using a Clinostat
Let’s go back to the experiment.
Clinostat
¥Used for controlling experiments
¥Contains a cork disc which can be set to
rotate in a vertical or horizontal plane by a
motor
¥Used to make factors uniform (evenly
distributed).
plastic cover lined with
moist blotting paper
seedling in X
X
in complete
darkness
seedling in Y
Y
What is the purpose of marking the radicles at
equal intervals ?
Answer: To find out which region of the radicle
grows faster.
plastic cover lined with
moist blotting paper
seedling in X
X
in complete
darkness
seedling in Y
Y
Does the direction of growth of the seedlings in
clinostats X and Y change ?
Answer: The radicle of the seedlings in clinostat X bends
downwards in response to the pull of gravity 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
seedling in X
X
in complete
darkness
seedling in Y
Y
What is the purpose of setting up clinostat Y ?
Ans: Serve as a control for comparison.
EXPERIMENT
NUMBER 3
To show Phototropism in
Shoots
Let’s start the experiment
A
unilateral
light
B
C
unilateral
light
light-proof
box
clinostat
in complete darkness
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 the shoots in pot C grow
vertically upwards with slender and longer nodes, and
carries smaller leaves which are yellow in colour.
A
unilateral
light
B
C
unilateral
light
light-proof
box
clinostat
in complete darkness
What is the effect of the clinostat on the shoot of plant B ?
Answer: The revolving clinostat cancel out the effect of unilateral
light on the shoot of plant B.
A
unilateral
light
B
C
unilateral
light
light-proof
box
clinostat
in complete darkness
What is the significance of phototropism to plants ?
Answer: This tropism ensures that a plant gets
enough light energy for photosynthesis.
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.
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
SOME OTHER
TYPES OF
TROPISM
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THIGMOTROPISM
Thigmotropism is the growth of a living organism in
response to a touch/contact. As in all tropisms there
exist positive and negative thigmotropism.
Positive thigmotropism is where a
living organism grows and clings to
a wall or a fence.
Negative thigmotropism is the
opposite. It is where a living organism
grows away from a touching object.
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HELIOTROPISM
Heliotropism is quite similar to phototropism. Now, as we know that
phototropism is the response of a living organism in response to
light but heliotropism is the diurnal motion of the plant flowers or
leaves in response to the direction of the sun. The most famous
examples of heliotropism is the sunflower. Heliotropism was first
described by Leonardo Da Vinci.
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THERMOTROPISM
Thermotropism is the tendency of plants or other organisms to bend
toward or away from heat. s the movement of a plant or plant part in
response to changes in temperature. A common example is the curling
of Rhododendron leaves in response to cold temperatures.
Thermotropism is often called thermotropic
movement .
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Chemotropism
Chemotropism is movement caused by chemical stimulus
in organisms such as bacteria and plants. An example of
chemotropic movement can be seen during the growth of
the pollen tube. This growth of the pollen tube is always
towards the ovules.
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