Transcript ppt_ch18e

18 Growth responses of green plants
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18.1 Do plants respond to external stimuli?
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18.2 What are tropisms?
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18.3 The growth response of shoots to light
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18.4 The growth response of roots and shoots to gravity
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18.5 The growth response of roots to water
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18.6 What are the substances for controlling growth
movements in plants?
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18.7 More about auxins
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18.8 The role of auxins in phototropic and geotropic responses
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Mind Map
18.1 Do plants respond to external stimuli?
18.1 Do plants respond to external stimuli?
Stimulus
Will it happen
YES!
Plants
Response
18.2 What are tropisms?
18.2 What are tropisms?
growth
Tropism
Response
plant
directional growth
movement
made by a plant
in response to a
unilateral stimulus
18.2 What are tropisms?
Direction of growth
towards stimulus
away from stimuli
positive tropism
negative tropism
stimulus
stimulus
plant
plant
18.2 What are tropisms?
light
Phototropism
Geotropism
Hydrotropism
water
H2O
H2O
H2O
H2O
H2O
gravity
18.3 The growth response of shoots to light
18.3 The growth response of shoots to light
Phototropism
shoot
root
18.3 The growth response of shoots to light
Phototropism
shoot
Positive
phototropism
root
Negative
phototropism
Importance:
Leaves can gain
maximum amount
of light for
photosynthesis
18.3 The growth response of shoots to light
Clinostat
18.3 The growth response of shoots to light
Clinostat
cancel out the effects of
unilateral light & gravity
by rotating the disc
set up as a control
for investigation of
growth responses
of roots & shoots to
unilateral light & gravity
direction of
rotation
18.3 The growth response of shoots to light
Experiment 18.1
To investigate the phototropic response of shoots
1. Select three pots of young seedlings of similar size and
label them as pots A, B and C respectively.
2. Put pot A in a lightproof box with a small
window on one side on
that light reaches the
shoot from one
direction only. This is
unilateral light.
light-proof
box
unilateral
light
set-up A
18.3 The growth response of shoots to light
Experiment 18.1
To investigate the phototropic response of shoots
3. Set up pot B in a similar way except that it is put on a
clinostat. Switch on the clinostat.
4. Put pot C in
unilateral
complete darkness. light
Both pots B and C
are controls.
light-proof box
in complete
darkness
clinostat
5. Observe the plants
after 1 or 2 days.
set-up B
set-up C
18.3 The growth response of shoots to light
Experiment 18.1
To investigate the phototropic response of shoots
Question 1:
What has happened to the shoots of plant A? Explain.
Answer:
Seedlings in pot A are exposed to unilateral
light. The shoots respond by growing
towards the light source.
18.3 The growth response of shoots to light
Experiment 18.1
To investigate the phototropic response of shoots
Question 2:
What has happened to the shoots of plant B? Explain.
Answer:
In pot B, as the effect of unilateral light is
cancelled out by the revolution of the
clinostat, the shoots do not show any
curvature but grow vertically upwards.
18.3 The growth response of shoots to light
Experiment 18.1
To investigate the phototropic response of shoots
Question 3:
What has happened to the shoots of plant C? Explain.
Answer:
In pot C, in complete darkness, the shoots
grow vertically upwards. The plant becomes
taller with slender and longer internodes, and
carries smaller leaves which are yellow in
colour. This condition is called etiolation.
18.3 The growth response of shoots to light
Experiment 18.1
To investigate the phototropic response of shoots
Question 4:
What is the significance of phototropism to plants?
Answer:
The shoot tends to grow towards the light source. This
phototropism ensures that a plant gets maximum light energy
for photosynthesis.
18.4 The growth response of roots & shoots to gravity
18.4 The growth response of roots & shoots to gravity
Geotropism
shoot
root
Gravity
ground
18.4 The growth response of roots & shoots to gravity
Geotropism
Importance:
Importance:
Negative
Positive
Geotropism Geotropism
leaves can
receive
maximal
sunlight for
photosynthesis
shoot
root
Gravity
grow deep
into soil to get
a firm
anchorage
roots can
absorb
ground
maximum
amount of
water and
mineral salts
18.4 The growth response of roots & shoots to gravity
Experiment 18.2
To study the geotropic response of roots and shoots
1. Add some moist wool in two Petri dishes.
2. Place three bean seedlings on the cotton wool in each Petri
dish.
Seedling P – placed horizontally
Seedling Q – with radicle pointing upwards
Seedling R – with radicle pointing downwards
18.4 The growth response of roots & shoots to gravity
Experiment 18.2
To study the geotropic response of roots and shoots
3. Cover the lid and place the whole Petri dish A with its edge
on a support.
4. Attach Petri dish B onto the cork disc of a clinostat.
in complete darkness
plumule
radicle
P1
Q1
Petri dishes
R1
in complete darkness
P2
Q2
R2
support
Set-up A
Set-up B
18.4 The growth response of roots & shoots to gravity
Experiment 18.2
To study the geotropic response of roots and shoots
5. Put both set-ups into a light-proof box.
6. Switch on the clinostat in set-up B.
7. Observe the seedlings after 1 or 2 days.
in complete darkness
plumule
radicle
P1
Q1
Petri dishes
R1
in complete darkness
P2
Q2
R2
support
Set-up A
Set-up B
18.4 The growth response of roots & shoots to gravity
Experiment 18.2
To study the geotropic response of roots and shoots
Question 1:
What has happened to the radicles and plumules in set-up A?
Draw a diagram to show the appearance of the seedlings.
P1
Answer:
The radicles grow downwards, while
the plumules grow upwards.
Q1
R1
18.4 The growth response of roots & shoots to gravity
Experiment 18.2
To study the geotropic response of roots and shoots
Question 2:
What has happened to the radicles and plumules in set-up B?
Draw a diagram to show the appearance of the seedlings.
Answer:
All the radicles and plumules
Q2
grow straight because the effect
of gravity is cancelled out by the
revolution of the clinostat.
P2
R2
18.4 The growth response of roots & shoots to gravity
Experiment 18.2
To study the geotropic response of roots and shoots
Question 3:
Question 4:
Why is it necessary to
leave the apparatus in
darkness?
Do the radicles and plumules show
positive geotropism or negative
geotropism?
Answer:
The apparatus is left
in darkness to avoid
the stimulus of light.
Answer:
In set-up A, the radicles grow
downwards and are positively
geotropic, while the plumules grow
upwards and are negatively geotropic.
18.4 The growth response of roots & shoots to gravity
Experiment 18.2
To study the geotropic response of roots and shoots
Question 5:
What advantage do the seedlings have by showing such
geotropism?
Answer:
Being positively geotropic, roots grow downwards deep into
the soil to provide a firm anchorage underground and absorb
maximum water and mineral salts in the soil. Being negatively
geotropic, shoots grow upwards to ensure that a plant gets
enough light energy for photosynthesis.
18.5 The growth response of roots to water
18.5 The growth response of roots to water
Hydrotropis
m
Wet
Dry
18.5 The growth response of roots to water
Hydrotropis
m
Importance:
get maximum water
as a raw material for
photosynthesis
get maximum mineral
salts to maintain
normal growth
No
response
Positive
Hydrotropism
Wet
Dry
18.5 The growth response of roots to water
Experiment 18.3
To investigate the relative effects of gravity and water on the
growth response of green plants
1. Prepare a 20cm X 20cm gauze square. Bend it to form a
shallow tray that is 2cm deep.
2. Place an even 1-cm deep layer of damp vermiculite.
3. Sprinkle about 20 pea seedlings onto the vermiculite. Cover
the seedlings with damp vermiculite.
18.5 The growth response of roots to water
Experiment 18.3
To investigate the relative effects of gravity and water on the
growth response of green plants
4. Set up the apparatus in
darkness as shown in
the diagram.
5. Observe the results
after 2 days.
water
18.5 The growth response of roots to water
Experiment 18.3
To investigate the relative effects of gravity and water on the
growth response of green plants
Question:
Which response is stronger, hydrotropic or geotropic? Explain.
Answer:
Some pea seedlings reverse their normal
geotropic response and grow upwards
water
towards the damp vermiculite. This
shows that hydrotropic response is
stronger than geotropic response.
18.6 What are the substances for controlling
growth movements in plants?
18.6 What are the substances for controlling
growth movements in plants?
coleoptile
first leaf
a protective sheath
surrounding the young
shoot of the embryo in
plants of the grass family
grass seed
used in the experiments
for finding out the factors
controlling the growth
movements in plants
18.6 What are the substances for controlling
growth movements in plants?
Charles Darwin (1880)
Experiment
Result
Conclusion /
Explanation
light
coleoptile
The coleoptile
grew towards
the light.
18.6 What are the substances for controlling
growth movements in plants?
Charles Darwin (1880)
Experiment
light
decapitated
coleoptile
Result
Conclusion /
Explanation
The shoot tip
was sensitive
to light.
18.6 What are the substances for controlling
growth movements in plants?
Charles Darwin (1880)
Experiment
opaque
cap
light
Result
Conclusion /
Explanation
This further
confirmed that
the tip was
sensitive to
light.
18.6 What are the substances for controlling
growth movements in plants?
Boysen-Jensen (1913)
Experiment
light
gelatin
allows
substances
to diffuse
down
light
Result
Conclusion /
Explanation
A substance
produced at
the tip diffused
through the
gelatin down
the shaded
side.
18.6 What are the substances for controlling
growth movements in plants?
Boysen-Jensen (1913)
Experiment
mica
plate
it does not
allow
substances
to diffuse
down
light
light
Result
Conclusion /
Explanation
Substance
causing the
bending
movement
moved down
the shaded side
of the shoot.
18.6 What are the substances for controlling
growth movements in plants?
Paal (1919)
Experiment
Result
Conclusion /
Explanation
A substance
had diffused
from the tip &
stimulated
growth.
18.6 What are the substances for controlling
growth movements in plants?
Fritz Went (1928)
Experiment
agar
block
stump
Result
Conclusion /
Explanation
The substance
passed from the
coleoptile tip into
the agar block
and then down
into the stump.
The stump bent
away from the
side with a source
of that substance.
18.6 What are the substances for controlling
growth movements in plants?
Fritz Went (1928)
Experiment
Result
Result
Went named
this substance
auxin
agar
block
stump
18.7 More about auxins
18.7 More about auxins
plant
hormone
organic
substances
auxin
auxin
auxin
can regulate
growth & other
physiological
processes
auxin
auxin
act on parts of the
plant other than the
part that produces
them
18.7 More about auxins
Site of production
shoot tip
produces auxins
auxins are
transported
downwards
to the root
roots tip also
produces a
small amount
of auxins
18.7 More about auxins
Site of production
mark at
2 mm
intervals
1
2
3
4
5
6
7
8
shoot tip
produces
auxins
1
2
3
4
5
6
7
8
auxin exert
their effect at
region of
elongation
18.7 More about auxins
Effect of auxins on different parts of a plant
No effect on
shoot growth
Lower
conc.
Higher
conc.
Inhibit root
growth
shoot
root
% growth
inhibition
% growth
stimulation
Stimulate
root growth
Stimulate
shoot
growth
Auxin concentration / parts per million (p.p.m.)
18.8
The role of auxins in phototropic & geotropic
responses
Phototropic
Geotropic
18.8
The role of auxins in phototropic & geotropic
responses
Phototropic
response of shoots
auxins
1
Unilateral light causes
auxins to accumulate
on the shaded side of
the shoot
18.8
2
The role of auxins in phototropic & geotropic
responses
Higher concentration of auxins
stimulates shoot growth
The shaded
side grows
faster than the
illuminated
side
4
The shoot grows
& bends towards
the light
3
18.8
The role of auxins in phototropic & geotropic
responses
Geotropic responses
of shoots and roots
gravity
Auxins diffuse down to the lower
side due to gravity
18.8
The role of auxins in phototropic & geotropic
responses
high concentration of
auxins inhibits root growth
high concentration of auxins
stimulates shoot growth
lower side of the root
grows more slowly
lower side of the shoot grows
faster than the upper side
the root bends
downwards
the shoot bends
upwards
Mind Map
Tropism
is caused by
growth movement
includes
geotropism
phototropism
auxins
unilateral
stimulus
which
are
produced
by
plant
hormones
shoot tips
and root tips
stimulate
growth at
region of
elongation in
shoots and roots
leaves gain
maximum
importamount of
ance
light for
photosynthesis
nature of
stimulus
nature of
stimulus
light
pull of gravity
illuminated
unilaterally
on shoots
auxins
move to
shaded side
so the
shoots
bending
toward
light source
on shoots
and roots
auxins
diffuse down
to lower side
so the
shoots
bending
upward
result
so the
roots
bending
downward
result
result
positive
response
by shoots
negative
response
by shoots
positive
response
by roots
hydrotropism
nature of
stimulus
water
result
positive
response
by roots
importance
roots can absorb
more water and
mineral salts
roots can
penetrate into
soil for
anchorage and
import- to absorb more
ance
water and
mineral salts