Transcript transpiration

1
Think about…
10.1 Transpiration
10.2 Transport in flowering plants
10.3 Support in plants
Recall ‘Think about…’
Summary concept map
2
3
The centre of the
trunk has rotted away.
But the tree is still
growing actively!
4
1
How can the tree
transport water and
food between its roots
and leaves with the
centre of its trunk
rotted away
5
2
What would happen
to the tree if the decay
occurred in the centre
of its roots instead of
the trunk Why
6
3
How can the tree
remain upright though
its trunk is hollow
7
10.1 Transpiration
water lost from
plant surface due
to evaporation
water absorbed
through roots
8
10.1 Transpiration
water lost from
plant surface due
to evaporation
water absorbed
transpiration
(蒸騰)
through roots
9
10.1
Transpiration
10.1
Demonstration of the occurrence of
transpiration
A
B
1 Use plastic bags
to enclose the
lower parts of the
plants and the
pots.
plastic bags
10
10.1
Transpiration
10.1
2 Put the intact potted
plant (A) inside a
bell jar. This is the
experimental
set-up.
A
B
plastic bags
11
10.1
Transpiration
10.1
3 Put the potted plant
(B) with the aerial
parts, i.e. parts
above the ground,
removed inside
another bell jar.
This is the control
set-up.
A
B
plastic bags
12
10.1
Transpiration
10.1
4 Leave both set-ups
in bright light for
2 hours.
A
B
plastic bags
13
10.1
Transpiration
10.1
5 Observe any changes
in the bell jars. Test
any liquid formed on
the walls with dry
cobalt(II) chloride
paper.
A
B
plastic bags
14
10.1
Transpiration
10.1
Results and discussion
• A layer of moisture and drops of liquid are
formed on the wall of bell jar A. The liquid
turns dry cobalt(II) chloride paper from
blue to pink, indicating the presence of
water.
15
10.1
Transpiration
10.1
Results and discussion
• Set-up B is the control. The bell jar
remains clear. No liquid is formed inside
the bell jar.
• The results show that water vapour is
released from plant A but not from plant B.
This indicates that transpiration takes
place in the aerial parts of the plant.
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10.1
Transpiration
10.1
Results and discussion
• The purpose of the pots enclosed in plastic
bags is to prevent the respiration of soil
organisms and the evaporation of soil
water from affecting the results.
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10.1
Transpiration
Where does
transpiration take
place?
18
10.1
Transpiration
leaf
stem
19
10.1
stem
Transpiration
leaf
20
10.1
Transpiration
leaf
10% of water
lost through
cuticle
90% of water
lost through
stomata
21
10.1
Transpiration
stem
very small
proportion of
water lost through
lenticels of
woody plants
22
10.1
Transpiration
How does transpiration take
place in leaves?
Animation
1 Water on the
surface of
mesophyll cells
evaporates into
the air space.
23
10.1
Transpiration
How does transpiration take
place in leaves?
2 Water vapour in
the air space
diffuses to the
atmosphere
through the
stoma.
24
10.1
Transpiration
Creation of transpiration pull
1 Water lost from
the surface of
mesophyll cells
is replaced by
water in these
cells.
25
10.1
Transpiration
Creation of transpiration pull
2 Water is drawn
from the
neighbouring
cells by osmosis.
26
10.1
Transpiration
Creation of transpiration pull
3 Water is finally
drawn from the
xylem vessels,
creating the
transpiration
pull (蒸騰拉力).
27
10.1
Transpiration
Significance of transpiration
1 During transpiration,
evaporation of
water absorbs heat
from the leaves.
cooling effect
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10.1
Transpiration
Significance of transpiration
2 Transpiration pulls
water up through
the plants.
transport of water
and minerals along
xylem vessels
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10.1
Transpiration
Significance of transpiration
3 Water and minerals
are drawn into the
roots from soil
during transpiration.
absorption of water
and minerals
30
10.1
How do we
measure the rate
of transpiration?
Transpiration
By using a
potometer
(蒸騰計).
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10.1
Transpiration
10.2
Video
Measurement of the rate of transpiration
using a bubble potometer
A bubble potometer can be used to measure
the rate of water uptake by a leafy shoot.
Since most of the water taken up by plants
will eventually be lost through transpiration,
it is assumed that the rate of water uptake is
the same as the rate of transpiration.
32
10.1
Transpiration
10.2
1 Cut a leafy shoot from a
plant and fit it tightly into
the bubble potometer under
water.
33
10.1
Transpiration
10.2
2 Set up the apparatus.
leafy shoot
reservoir
graduated
tap (closed) capillary tube
bubble
water
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10.1
Transpiration
10.2
3 Seal off all connections with vaseline to
ensure no water leakage.
4 Lift the end of the capillary tube from the
beaker of water for 30 seconds and then
replace it to introduce an air bubble into
the tube.
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10.1
Transpiration
10.2
5 Wait for the bubble to move into the
horizontal graduated part of the capillary
tube.
6 Record the distance travelled by the bubble
in a certain period of time (e.g. 5 minutes).
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10.1
Transpiration
10.2
Results and discussion
• The rate of water uptake can be found out
by calculating the rate of movement of
the air bubble, i.e. distance travelled by
the air bubble per unit time.
This is an indirect measurement of the
rate of transpiration.
37
10.1
Transpiration
10.2
Results and discussion
• The leafy shoot should be cut and fit into
the potometer under water. This prevents
air bubbles from entering the xylem
vessels of the plant and blocking water
uptake.
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10.1
Transpiration
10.3
Video
Measurement of the amount of water
absorbed and lost by a plant using a
weight potometer
A weight potometer is comprised of two parts:
(1) the burette which is used to measure the
rate of water uptake by a leafy shoot
(2) the balance which is used to measure the
rate of water loss by the leafy shoot.
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10.1
Transpiration
10.3
1 Cut a leafy shoot from a plant and fit it
tightly into the weight potometer under
water.
2 Set up the apparatus as shown.
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10.1
Transpiration
10.3
oil layer
burette
water
leafy shoot
top pan
balance
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10.1
Transpiration
10.3
3 Record the initial water level (Vi) in the
burette and the weight (Wi) of the entire
set-up.
4 After 24 hours, record the final water level
(Vf) in the burette and the weight (Wf) of
the entire set-up.
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10.1
Transpiration
10.3
Results and discussion
The amount of water absorbed by the plant
= the change in volume of water in the burette
= (Vf –Vi)
The amount of water lost by the plant
= the change in weight of the entire set-up
= (Wf –Wi)
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10.1
Transpiration
10.3
Results and discussion
The amount of water absorbed is slightly
greater than the amount of water lost by
the plant.
This is because some water is used in
photosynthesis, growth and other metabolic
activities.
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10.1
Transpiration
Factors affecting the rate of
transpiration
1 Light intensity
2 Air movement
3 Relative humidity
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10.1
Transpiration
1 Light intensity
rate of
transpiration
light intensity 
stomata open wider
more water vapour
diffuses out
transpiration rate 
light intensity
46
10.1
Transpiration
2 Air movement
rate of
transpiration
wind blows away
water vapour
around the stomata
steep concentration
gradient of water
vapour maintained
wind speed
47
10.1
Transpiration
2 Air movement
rate of
transpiration
diffusion rate 
transpiration rate 
wind speed
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10.1
Transpiration
3 Relative humidity
rate of
transpiration
relative humidity of
surrounding air 
concentration
gradient of water
vapour 
relative humidity
49
10.1
Transpiration
3 Relative humidity
rate of
transpiration
less water vapour
diffuses out
transpiration rate 
relative humidity
50
10.1
Transpiration
10.4
Simulation
Design an investigation of the effects
of environmental factors on the rate of
transpiration
Donna put some roses in her bathroom and
some in the sitting room.
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10.1
Transpiration
10.4
Later, she found that the water level in the
vase placed in the sitting room was much
lower than that in the bedroom.
She wondered that
environmental
conditions had
affected transpiration
and water uptake by
the plants.
52
10.1
Transpiration
10.4
Design and perform an investigation to
find out the effect of an environmental
factor on the rate of transpiration.
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10.1
Transpiration
1 Transpiration is the loss of water
vapour from the surface of plants
due to evaporation .
It occurs through stomata of
leaves, lenticels of woody stems
and cuticle .
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10.1
Transpiration
2a During transpiration, water flows
from:
xylem in leaves
mesophyll cells
air space
atmosphere
55
10.1
Transpiration
2b When water is continuously
removed from the xylem vessels
in leaves, a force called
transpiration
pull is created to
transpiration
pull
pull water up the xylem vessels
from the roots.
56
10.1
Transpiration
3 Importance of transpiration to plants:
• produces a cooling effect on
plants
• results in transport of water
and minerals along xylem
vessels
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10.1
Transpiration
3 Importance of transpiration to plants:
• aids in absorption of water
and minerals from the soil into
the roots
58
10.1
Transpiration
4 Factors affecting rate of transpiration:
• light intensity increases
• air movement increases
rate of transpiration increases
59
10.1
Transpiration
4 Factors affecting rate of transpiration:
• relative humidity increases
rate of transpiration decreases
60
10.2 Transport in flowering plants
Do flowering plants
have a transport
system like ours?
61
10.2
Transport in flowering plants
• transport in flowering plants is provided
by vascular bundles (維管組織)
xylem
phloem
3D animation
their distribution in roots,
stems and leaves are different
62
10.2
Transport in flowering plants
Distribution of vascular bundles
LEAF
midrib vein leaf vein
• in large central midrib and
network of small veins
63
10.2
Transport in flowering plants
Distribution of vascular bundles
LEAF
xylem
phloem
64
10.2
Transport in flowering plants
Distribution of vascular bundles
LEAF
xylem
phloem
65
10.2
Transport in flowering plants
Distribution of vascular bundles
STEM
• arranged in a
ring at the
periphery
xylem phloem
66
10.2
Transport in flowering plants
Distribution of vascular bundles
STEM
xylem phloem
67
10.2
Transport in flowering plants
Distribution of vascular bundles
STEM
xylem phloem
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10.2
Transport in flowering plants
Distribution of vascular bundles
• at the centre
ROOT
phloem
xylem
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10.2
Transport in flowering plants
Distribution of vascular bundles
ROOT
xylem phloem
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10.2
Transport in flowering plants
Distribution of vascular bundles
ROOT
xylem phloem
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10.2
Transport in flowering plants
10.5
Video
Examination of the vascular tissues of
a young dicotyledonous plant
1 Prepare temporary mounts of the transverse
sections of the leaf, stem and root of a
young dicotyledonous plant.
Examine them or prepared slides under
low power magnification.
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10.2
Transport in flowering plants
10.5
2 Identify the vascular tissues in each of the
slides. Draw labelled diagrams of them.
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10.2
Transport in flowering plants
How are xylem and
phloem adapted to
transport substances?
74
10.2
Transport in flowering plants
1 Xylem
• transports water and minerals
• consists of xylem vessels
(木質導管)
75
10.2
Transport in flowering plants
1 Xylem
thick and
lignified cell
wall
provides
support
76
10.2
Transport in flowering plants
1 Xylem
continuous
hollow tube
no cytoplasm
or nuclei
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10.2
Transport in flowering plants
1 Xylem
continuous
hollow tube
allows water to
move with little
resistance
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10.2
Transport in flowering plants
1 Xylem
no end wall
between cells
allows water to
move from one
cell to another
79
10.2
Transport in flowering plants
10.6
Video
Investigation of the plant tissue
responsible for water transport
Eosin is a red dye. When a plant absorbs the
eosin solution, the tissue responsible for
transporting water would be stained red.
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10.2
Transport in flowering plants
10.6
1 Immerse the roots of a
herbaceous plant in dilute eosin
solution for about 30 minutes.
eosin solution
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10.2
Transport in flowering plants
10.6
2 Cut transverse sections of the
root, stem and leaf of the plant.
Examine them under a
microscope. Identify the
tissue(s) stained red.
eosin solution
82
10.2
Transport in flowering plants
10.6
Results and discussion
In the root, stem and leaf sections, only the
xylem vessels are stained red.
This shows that water is transported along
the xylem vessels in the plant.
83
10.2
Transport in flowering plants
2 Phloem
• transports organic nutrients
• consists of sieve tubes (篩管)
and companion cells (伴細胞)
84
10.2
Transport in flowering plants
2 Phloem
living sieve
tube
has cytoplasm
but no nucleus
85
10.2
Transport in flowering plants
2 Phloem
living sieve
tube
allows nutrients
to move with
little resistance
86
10.2
Transport in flowering plants
2 Phloem
sieve plate (篩
板)
has pores for
nutrients to
pass through
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10.2
Transport in flowering plants
2 Phloem
companion cell
has cytoplasm
and a nucleus
88
10.2
Transport in flowering plants
2 Phloem
companion cell
supports
metabolism of
sieve tubes
89
10.2
Transport in flowering plants
How are water and minerals
transported?
Water and minerals are absorbed in roots
90
10.2
Transport in flowering plants
How are water and minerals
transported?
The main driving force is
the transpiration pull
Water and minerals are absorbed in roots
91
10.2
Transport in flowering plants
How are water and minerals
upper epidermis
transported?
of the leaf
xylem vessel
in leaf
xylem vessel
in stem
stoma
92
root hair
10.2
Transport in flowering plants
How are water and minerals
transported?
1 Water evaporates
from the mesophyll
cells and diffuses
out through stomata.
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10.2
Transport in flowering plants
How are water and minerals
transported?
2 Water is drawn from
neighbouring cells,
then from the xylem
vessel.
94
10.2
Transport in flowering plants
How are water and minerals
transported?
3 Water is drawn up
the xylem vessel by
transpiration pull.
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10.2
Transport in flowering plants
How are water and minerals
transported?
4 Water is drawn into
the roots from the
soil by osmosis.
96
10.2
Transport in flowering plants
How are organic nutrients
transported?
bud
leaf
stem
fruit
roots
97
10.2
Transport in flowering plants
How are organic nutrients
transported?
1 Organic nutrients
are made in
leaves by
photosynthesis.
98
10.2
Transport in flowering plants
How are organic nutrients
transported?
2a Nutrients move
down to
growing fruits
and roots for
storage.
99
10.2
Transport in flowering plants
How are organic nutrients
transported?
2bNutrients move
up to buds for
growth and
development.
100
10.2
Transport in flowering plants
How are organic nutrients
transported?
2bNutrients move
up to buds for
growth and
development.
translocation
(輸導)
101
10.2
Transport in flowering plants
1 In flowering plants, materials are
transported in vascular bundles
that consist of xylem and
phloem .
phloem
102
10.2
Transport in flowering plants
2 Xylem mainly consists of
xylem
vessels which are continuous
vessels
hollow
hollow tubes made up of dead
cells joined end to end.
103
10.2
Transport in flowering plants
3a Phloem consists of
sieve tubes
and companion cells .
104
10.2
Transport in flowering plants
3b Each sieve tube is a column of
sieve cells joined end to end. The
end walls between cells have
sieve
many pores
pores , forming the sieve
plates
plates .
105
10.2
Transport in flowering plants
4 In flowering plants, water and
xylem
minerals are transported in xylem
vessels
vessels from the roots up to the
other parts of the plant. It is mainly
driven by transpiration pull .
106
10.2
Transport in flowering plants
5 In flowering plants, organic nutrients
are transported along phloem
from the leaves to the growing
regions or storage organs. This
process is called translocation .
107
10.3 Support in plants
Terrestrial plants need to stand upright
and stretch out their branches to:
• receive maximum amount of
sunlight
• favour pollination and dispersal
of fruits and seeds
108
10.3 Support in plants
support (支持) in plants
turgidity of
thin-walled cells
rigidity of
thick-walled cells
109
10.3 Support in plants
turgidity of
thin-walled cells
cortex
pith
110
10.3
Support in plants
Turgidity of thin-walled cells
When water supply is adequate …
xylem has a higher
water potential
than the cells in
cortex and pith
xylem
111
10.3
Support in plants
Turgidity of thin-walled cells
When water supply is adequate …
water moves from
the xylem into
these cells by
osmosis
112
10.3
Support in plants
Turgidity of thin-walled cells
When water supply is adequate …
cells become
turgid and press
against each other
113
10.3
Support in plants
Turgidity of thin-walled cells
When water supply is adequate …
turgidity makes the
whole stem strong
enough to stand
upright
114
10.3
Support in plants
Turgidity of thin-walled cells
When water supply is inadequate …
cells in the cortex
and pith will
become flaccid
115
10.3
Support in plants
Turgidity of thin-walled cells
When water supply is inadequate …
cells can no longer
support the stem
and the plant wilts
(凋謝)
116
10.3
Support in plants
support (支持) in plants
turgidity of
thin-walled cells
rigidity of
thick-walled cells
117
10.3
Support in plants
hard and rigid
thick, lignified
cell wall
xylem vessels
rigidity of
thick-walled cells
118
10.3
Support in plants
Rigidity of thick-walled cells
xylem
cells
cross-section
of a young
woody stem
new
xylem cell
As a woody plant grows,
more and more xylem is
formed
119
10.3
Support in plants
Rigidity of thick-walled cells
next new
xylem cell
cross-section
of a young
woody stem
mature
xylem cell
The older xylem tissues in
stems are pushed inwards
120
10.3
Support in plants
Rigidity of thick-walled cells
cross-section
of a young
woody stem
new
xylem cell
mature
xylem cell
wood
They finally become hard
wood tissues
provide support
121
10.3
Support in plants
1 Dicotyledonous plants are
supported by the turgidity of
thin-walled cells in the cortex and
pith of stem.
122
10.3
Support in plants
2 Woody plants are supported mainly
by the rigidity of thick-walled cells
containing lignin .
123
1
How can the tree transport water and
food between its roots and leaves with
the centre of its trunk rotted away?
The vascular tissues remain unaffected
because they are located at the
periphery.
124
2
What would happen to the tree if the
decay occurred in the centre of its roots
instead of the trunk? Why?
No substances can be transported and
the tree will die soon because the
vascular tissues are located at the
central part.
125
3
How can the tree remain upright
though its trunk is hollow?
The thick-walled cells at the periphery
of the stem are strong enough to
provide support.
126
Plants
lose water in
transpiration
transpiration
creates
pull
affected
by
light
air
relative
intensity movement humidity
127
Plants
transport takes place in
vascular tissue
consists of
xylem
phloem
128
xylem
mainly consists of
xylem vessels
transport
water
minerals
129
phloem
consists of
sieve tubes
companion cells
transport
organic nutrients
130
Plants
gain support by
turgidity of
thin-walled
cells
rigidity of
thick-walled
cells
131
132