1 2 think about… 10.1 transpiration 10.2 transport in flowering plants 10.3 support in plants...
TRANSCRIPT
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Think about…
10.1 Transpiration
10.2 Transport in flowering plants
10.3 Support in plants
Recall ‘Think about…’
Summary concept map
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The centre of the trunk has rotted away. But the tree is still growing actively!
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How can the tree1transport water and food between its roots and leaves with the centre of its trunk rotted away
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What would happen2to the tree if the decay occurred in the centre of its roots instead of the trunk Why
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How can the tree3remain upright though its trunk is hollow
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10.1 Transpiration
water absorbed through roots
water lost from plant surface due to evaporation
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10.1 Transpiration
water absorbed through roots
water lost from plant surface due to evaporation
transpiration (蒸騰 )
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1 Use plastic bags to enclose the lower parts of the plants and the pots.
10.1
Demonstration of the occurrence of transpiration
10.1 Transpiration
plastic bags
A B
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10.1
10.1 Transpiration
plastic bags
A B
2 Put the intact potted plant (A) inside a bell jar. This is the experimental set-up.
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10.1
10.1 Transpiration
plastic bags
A B
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.
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10.1
10.1 Transpiration
plastic bags
A B
4 Leave both set-ups in bright light for 2 hours.
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10.1
10.1 Transpiration
plastic bags
A B
5 Observe any changes in the bell jars. Test any liquid formed on the walls with dry cobalt(II) chloride paper.
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10.1
Results and discussion
10.1 Transpiration
• 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.
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10.1
Results and discussion
10.1 Transpiration
• 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
Results and discussion
10.1 Transpiration
• 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?
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10.1 Transpiration
leaf
stem
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10.1 Transpiration
stem leaf
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10.1 Transpiration
10% of water lost through cuticle
90% of water lost through stomata
leaf
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10.1 Transpiration
very small proportion of water lost through lenticels of woody plants
stem
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How does transpiration take place in leaves?
10.1 Transpiration
Animation
1 Water on the surface of mesophyll cells evaporates into the air space.
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How does transpiration take place in leaves?
10.1 Transpiration
2 Water vapour in the air space diffuses to the atmosphere through the stoma.
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Creation of transpiration pull10.1 Transpiration
1 Water lost from the surface of mesophyll cells is replaced by water in these cells.
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Creation of transpiration pull10.1 Transpiration
2 Water is drawn from the neighbouring cells by osmosis.
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Creation of transpiration pull10.1 Transpiration
3 Water is finally drawn from the xylem vessels, creating the transpiration pull (蒸騰拉力 ).
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Significance of transpiration10.1 Transpiration
1 During transpiration, evaporation of water absorbs heat from the leaves.
cooling effect
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Significance of transpiration10.1 Transpiration
2 Transpiration pulls water up through the plants.
transport of water and minerals along
xylem vessels
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Significance of transpiration10.1 Transpiration
3 Water and minerals are drawn into the roots from soil during transpiration.
absorption of water and minerals
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10.1 Transpiration
How do we measure the rate of transpiration?
By using a potometer (蒸騰計 ).
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A bubble potometer can be used to measure the rate of water uptake by a leafy shoot.
10.2
Measurement of the rate of transpiration using a bubble potometer
Video
10.1 Transpiration
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.
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10.2
10.1 Transpiration
1 Cut a leafy shoot from a plant and fit it tightly into the bubble potometer under water.
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10.2
2 Set up the apparatus.
10.1 Transpiration
leafy shoot
reservoir
tap (closed)
graduated capillary tube
bubblewater
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10.2
10.1 Transpiration
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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10.2
10.1 Transpiration
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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10.2
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.
10.1 Transpiration
This is an indirect measurement of the rate of transpiration.
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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.
10.1 Transpiration
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A weight potometer is comprised of two parts:
10.3
Measurement of the amount of water absorbed and lost by a plant using a weight potometer
Video
10.1 Transpiration
(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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10.3
10.1 Transpiration
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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10.3
10.1 Transpiration
buretteoil layer
water leafy shoot
top pan balance
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10.3
10.1 Transpiration
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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10.3
10.1 Transpiration
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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10.3
10.1 Transpiration
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
1 Light intensity
Factors affecting the rate of transpiration
2 Air movement
3 Relative humidity
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1 Light intensity10.1 Transpiration
rate of transpiration
light intensity
light intensity
stomata open wider
more water vapour diffuses out
transpiration rate
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2 Air movement10.1 Transpiration
rate of transpiration
wind speed
wind blows away water vapour around
the stomata
steep concentration gradient of water vapour maintained
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2 Air movement10.1 Transpiration
rate of transpiration
wind speed
diffusion rate
transpiration rate
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3 Relative humidity10.1 Transpiration
rate of transpiration
relative humidity
relative humidity of surrounding air
concentration gradient of water vapou
r
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3 Relative humidity10.1 Transpiration
rate of transpiration
less water vapour diffuses out
transpiration rate
relative humidity
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Donna put some roses in her bathroom and some in the sitting room.
10.4
Design an investigation of the effects of environmental factors on the rate of transpiration
Simulation
10.1 Transpiration
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10.4
10.1 Transpiration
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.
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10.4
10.1 Transpiration
Design and perform an investigation to find out the effect of an environmental factor on the rate of transpiration.
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It occurs through of leaves, of woody stems and .
1 Transpiration is the loss of water vapour from the surface of plants due to .evaporation
stomatalenticels
10.1 Transpiration
cuticle
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mesophyll
air space
2a During transpiration, water flows from:xylem
10.1 Transpiration
in leaves
cells
atmosphere
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2bWhen water is continuously removed from the xylem vessels in leaves, a force called transpiration pull is created to pull water up the xylem vessels from the roots.
transpiration pull
10.1 Transpiration
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• results in transport of and along xylem vessels
• produces a effect on plants
3 Importance of transpiration to plants:
cooling
10.1 Transpiration
waterminerals
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• aids in of water and minerals from the soil into the roots
3 Importance of transpiration to plants:
absorption
10.1 Transpiration
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• increases
• increases4 Factors affecting rate of transpiration:
light intensity
air movement
rate of transpiration increases
10.1 Transpiration
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• increases4 Factors affecting rate of transpiration:
relative humidity
rate of transpiration decreases
10.1 Transpiration
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10.2 Transport in flowering plants
Do flowering plants have a transport system like ours?
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10.2 Transport in flowering plants
3D animation
• transport in flowering plants is provided by vascular bundles (維管組織 )
xylem phloem
their distribution in roots, stems and leaves are different
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10.2 Transport in flowering plants
leaf veinmidrib vein
• in large central midrib and network of small veins
LEAF
Distribution of vascular bundles
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10.2 Transport in flowering plants
LEAF
xylem
phloem
Distribution of vascular bundles
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10.2 Transport in flowering plants
LEAF
Distribution of vascular bundles
xylemphloem
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10.2 Transport in flowering plants
STEM
xylem phloem
• arranged in a ring at the periphery
Distribution of vascular bundles
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10.2 Transport in flowering plants
STEM
xylem phloem
Distribution of vascular bundles
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10.2 Transport in flowering plants
STEM
Distribution of vascular bundles
xylem phloem
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10.2 Transport in flowering plants
ROOT
xylemphloem
• at the centre
Distribution of vascular bundles
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10.2 Transport in flowering plants
ROOT
xylem phloem
Distribution of vascular bundles
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10.2 Transport in flowering plants
ROOT
xylem phloem
Distribution of vascular bundles
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10.5
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.
10.2 Transport in flowering plants
Video
Examine them or prepared slides under low power magnification.
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10.5
2 Identify the vascular tissues in each of the slides. Draw labelled diagrams of them.
10.2 Transport in flowering plants
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10.2 Transport in flowering plants
How are xylem and phloem adapted to
transport substances?
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1 Xylem10.2 Transport in flowering plants
• transports water and minerals• consists of xylem vessels
(木質導管 )
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1 Xylem10.2 Transport in flowering plants
provides support
thick and lignified cell wall
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1 Xylem10.2 Transport in flowering plants
no cytoplasm or nuclei
continuous hollow tube
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1 Xylem10.2 Transport in flowering plants
allows water to move with little resistance
continuous hollow tube
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1 Xylem10.2 Transport in flowering plants
allows water to move from one cell to another
no end wall between cells
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10.6
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.
10.2 Transport in flowering plants
Video
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10.6
1 Immerse the roots of a herbaceous plant in dilute eosin solution for about 30 minutes.
10.2 Transport in flowering plants
eosin solution
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10.6
10.2 Transport in flowering plants
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
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10.6
10.2 Transport in flowering plants
Results and discussionIn 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.
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2 Phloem10.2 Transport in flowering plants
• transports organic nutrients• consists of sieve tubes (篩管 ) and companion cells (伴細胞 )
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2 Phloem10.2 Transport in flowering plants
has cytoplasm but no nucleus
living sieve tube
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2 Phloem10.2 Transport in flowering plants
allows nutrients to move with little resistance
living sieve tube
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2 Phloem10.2 Transport in flowering plants
has pores for nutrients to pass through
sieve plate (篩板 )
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2 Phloem10.2 Transport in flowering plants
has cytoplasm and a nucleus
companion cell
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2 Phloem10.2 Transport in flowering plants
supports metabolism of sieve tubes
companion cell
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How are water and minerals transported?
10.2 Transport in flowering plants
Water and minerals are absorbed in roots
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How are water and minerals transported?
10.2 Transport in flowering plants
The main driving force is the transpiration pull
Water and minerals are absorbed in roots
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How are water and minerals transported?
10.2 Transport in flowering plants
xylem vessel in leaf
xylem vessel in stem
root hair
upper epidermis of the leaf
stoma
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How are water and minerals transported?
10.2 Transport in flowering plants
1 Water evaporates from the mesophyll cells and diffuses out through stomata.
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How are water and minerals transported?
10.2 Transport in flowering plants
2 Water is drawn from neighbouring cells, then from the xylem vessel.
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How are water and minerals transported?
10.2 Transport in flowering plants
3 Water is drawn up the xylem vessel by transpiration pull.
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How are water and minerals transported?
10.2 Transport in flowering plants
4 Water is drawn into the roots from the soil by osmosis.
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How are organic nutrients transported?
10.2 Transport in flowering plants
leaf
bud
fruitstem
roots
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How are organic nutrients transported?
10.2 Transport in flowering plants
1 Organic nutrients are made in leaves by photosynthesis.
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How are organic nutrients transported?
10.2 Transport in flowering plants
2aNutrients move down to growing fruits and roots for storage.
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How are organic nutrients transported?
10.2 Transport in flowering plants
2bNutrients move up to buds for growth and development.
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How are organic nutrients transported?
10.2 Transport in flowering plants
2bNutrients move up to buds for growth and development.
translocation (輸導 )
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1 In flowering plants, materials are transported in vascular bundles that consist of and phloem .
xylemphloem
10.2 Transport in flowering plants
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2 Xylem mainly consists of vessels which are continuous hollow tubes made up of dead cells joined end to end.
xylem
hollow
10.2 Transport in flowering plants
vessels
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3a Phloem consists of and .
sieve tubescompanion cells
10.2 Transport in flowering plants
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3bEach sieve tube is a column of sieve cells joined end to end. The end walls between cells have many pores , forming the sieve plates .
pores sieveplates
10.2 Transport in flowering plants
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4 In flowering plants, water and minerals are transported in xylem vessels from the roots up to the other parts of the plant. It is mainly driven by .
10.2 Transport in flowering plants
xylem
transpiration pull
vessels
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5 In flowering plants, organic nutrients are transported along from the leaves to the growing regions or storage organs. This process is called .
10.2 Transport in flowering plants
phloem
translocation
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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
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10.3 Support in plants
support (支持 ) in plants
turgidity of thin-walled cells
rigidity of thick-walled cells
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10.3 Support in plants
turgidity of thin-walled cells
cortex
pith
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Turgidity of thin-walled cells10.3 Support in plants
When water supply is adequate …
xylem has a higher water potential than the cells in cortex and pith
xylem
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Turgidity of thin-walled cells10.3 Support in plants
When water supply is adequate …
water moves from the xylem into these cells by osmosis
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Turgidity of thin-walled cells10.3 Support in plants
When water supply is adequate …
cells become turgid and press against each other
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Turgidity of thin-walled cells10.3 Support in plants
When water supply is adequate …
turgidity makes the whole stem strong enough to stand upright
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Turgidity of thin-walled cells10.3 Support in plants
When water supply is inadequate …
cells in the cortex and pith will become flaccid
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Turgidity of thin-walled cells10.3 Support in plants
When water supply is inadequate …
cells can no longer support the stem and the plant wilts (凋謝 )
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support (支持 ) in plants
turgidity of thin-walled cells
rigidity of thick-walled cells
10.3 Support in plants
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rigidity of thick-walled cellsxylem vessels
thick, lignified cell wall
hard and rigid
10.3 Support in plants
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Rigidity of thick-walled cells10.3 Support in plants
cross-section of a young
woody stem
xylem cells
new xylem cell
As a woody plant grows, more and more xylem is formed
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Rigidity of thick-walled cells10.3 Support in plants
cross-section of a young
woody stemThe older xylem tissues in stems are pushed inwards
next new xylem cell
mature xylem cell
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Rigidity of thick-walled cells10.3 Support in plants
cross-section of a young
woody stemThey finally become hard wood tissues
new xylem cell
mature xylem cell
wood
provide support
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1 Dicotyledonous plants are supported by the of thin-walled cells in the cortex and pith of stem.
turgidity
10.3 Support in plants
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2Woody plants are supported mainly by the of thick-walled cells containing .
rigidity
10.3 Support in plants
lignin
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How can the tree transport water and food between its roots and leaves with the centre of its trunk rotted away?
1
The vascular tissues remain unaffected because they are located at the periphery.
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What would happen to the tree if the decay occurred in the centre of its roots instead of the trunk? Why?
2No substances can be transported and the tree will die soon because the vascular tissues are located at the central part.
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How can the tree remain upright though its trunk is hollow?3
The thick-walled cells at the periphery of the stem are strong enough to provide support.
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affected by
creates
Plants
transpiration transpiration pull
lose water in
light intensity
air movement
relative humidity
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consists of
vascular tissue
transport takes place in
xylem phloem
Plants
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transport
xylem vessels
mainly consists of
water minerals
xylem
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transport
sieve tubes
consists of
organic nutrients
phloem
companion cells
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gain support by
turgidity of thin-walled
cells
rigidity of thick-walled
cells
Plants
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