BackNext Home 1 BackNext Home 2 Think about it 10.1How is water lost in transpiration?How is water...

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Think about it

10.1 How is water lost in transpiration?

10.2How are water and minerals absorbed in the roots?

10.3How are water, minerals and organic nutrients transported inside plants?

10.4 How are plants supported?

Practical 10.1 Practical 10.2 Practical 10.3

Practical 10.4 Practical 10.5 Practical 10.6

Practical 10.7 Practical 10.8

Summary concept diagram

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Have you seen artificially coloured flowers before?

Sally has bought a bunch of coloured flowers.

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Home 4How are flowers artificially made?

Sally has bought a bunch of coloured flowers.

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Home 5How are flowers artificially made?

Sally has bought a bunch of coloured flowers.You can make coloured flowers by putting white flowers, e.g. carnations (康乃馨 ), into a solution of food colouring.

The solution is absorbed and transported to the petals so that they turn to the colour of the food colouring after several days.

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All organisms lose water all the time.

In plants: through transpiration (蒸騰作用 )

H2O

H2O

H2O

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The water lost must be quickly replaced.

by absorption from soil in the roots

H2OH2O

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The loss of water vapour from the surfaces of plants due to evaporation.

Definition of transpiration:

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> 90% of the total water loss from stomata

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very small amount of water lost through cuticle

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10.1 How is water lost in transpiration? < 10% of water loss through lenticels (皮孔 )

in woody stems

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10.1Demonstration of the occurrence of transpiration

Procedure:1 Set up the apparatus as shown in the diagram.

intactpottedplant

bell jars

plastic bags

potted plant with the aerial parts removed

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2 Leave both set-ups in bright light for 2 hours.

Procedure:

intactpottedplant

bell jars

plastic bags


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3 Observe any changes in the bell jars. Test any liquid formed on the walls with dry cobalt (II) chloride paper.

intactpottedplant

bell jars

plastic bags


Procedure:

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TranspirationTranspirationThe process of transpiration

1) Water on the surface of the mesophyll cells evaporates into the air space.

A leaf section

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TranspirationTranspirationThe process of transpiration

2) Water vapour diffuses through the stomata to the outside down the concentration gradient.

A leaf section

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TranspirationTranspirationThe creation of

transpiration pull1) Water is lost from the

permeable cell wall, which is replaced by water in the cell.

A leaf section

Each cell then draws water from its neighbouring cells.

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TranspirationTranspirationThe creation of

transpiration pull2) Cells draw water from

the xylem vessels, pulling water up the plant.

A leaf section

transpiration pull (蒸騰牽引力 ) is created

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TranspirationTranspirationImportance of transpiration

1) produces a cooling effect in the plant and helps leaves withstand high temperatures

2) helps in the absorption of water and minerals from the soil

3) causes the transport of water and minerals in plants

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Distribution of stomata on leaves in terrestrial and aquatic plants

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10.2Design an investigation of the distribution of stomata on both sides of a leaf

Bobby observed that the dry cobalt (II) chloride paper on the underside of the leaf changed from blue to pink faster than the one on the upper surface.

sellotape

dry cobalt (ll)chloride paper

on both sides of the leaf

potted plant

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He wondered if the result was due to different stomatal densities of both sides of the leaf.

sellotape



potted plant

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Design and perform an experiment to compare the distribution of stomata on both sides of a leaf.

sellotape



potted plant

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Terrestrial dicotyledonous plants• more stomata in the lower

epidermis than the upper epidermis

• fewer stomata in the upper epidermis: reduce water loss

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Submerged leaves of aquatic plants• no cuticle

• gases, water and minerals diffuse directly all over their surface

• few or no stomata in the upper and lower epidermis

換 wb 金魚草相

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Floating leaves of aquatic plants• have stomata in the upper

epidermis only

• no stomata in the lower epidermis

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Plant speciesNumber of stomata per cm2

Upper epidermis Lower epidermis

Terrestrial dicotyledons

Apple

Tomato

Submerged leaves of aquatic plants

Hydrilla

Floating leaves of aquatic plants

Water lily

1 200

0

9 500

013 000

0

0

14 100

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Measuring the rate of transpiration

• with a potometer (蒸騰計 )

a potometer

Extension

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10.3Measurement of the rate of transpiration using a bubble potometer

Procedure:1 Cut a leafy shoot from a p

lant and fit it tightly into the bubble potometer under water. Set up the apparatus as shown. Seal off all connections with vaseline to ensure no leakage of water.

leafy shoot

reservoir

tap (closed)

air bubble

graduated capillary tube

water

beaker

Extension

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Procedure:2 Lift the end of the capillar

y tube from the beaker of water for 30 s and then replace it to introduce an air bubble into the tube.

leafy shoot

reservoir

tap (closed)

air bubble


water

beaker

Extension

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Procedure:3 Wait for the bubble to mo

ve into the horizontal graduated part of the capillary tube.

leafy shoot

reservoir

tap (closed)

air bubble


water

beaker

4 Record the distance travelled by the bubble in a certain period of time (e.g. 5 minutes).

Extension

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10.4Measurement of the amount of water absorbed and lost by a plant using a weight potometer

Procedure:1 Cut a leafy shoot from a plan

t and fit it tightly into the weight potometer under water.

leafy shoot

burette

top pan balance

water

oil layer

2 Set up the apparatus as shown.

Extension

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10.4Measurement of the amount of water absorbed and lost by a plant using a weight potometer

Procedure:3 Record the initial water level (V

i) in the burette and the weight (Wi) of the whole set-up.

leafy shoot

burette

top pan balance

water

oil layer

4 After 24 hours, record the final water level (Vf) and the weight (Wf) of the whole set-up.

Extension

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Effects of the environmental factors on the rate of transpiration

Extension

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10.5Design an investigation of the effects of environmental factors on the rate of transpiration

Donna put some roses in her bedroom and some in the sitting room.

Extension

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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 if the environmental conditions have affected transpiration and water uptake of the flowers.

Extension

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Design and perform an experiment to find out the effects of an environmental factor on the rate of transpiration.

Extension

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1 Light intensity

rate

of

tran

spir

atio

n

light intensity

• light intensity, the stomata open wider more water vapour in the a

ir space can diffuse out

rate of transpiration

Extension

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2 Temperature

rate

of

tran

spir

atio

n

temperature

• temperature

(2) relative humidity


Extension

(1) rate of evaporation and rate of diffusion of water vapour out of stomata


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3 Relative humidity

rate

of

tran

spir

atio

n

relative humidity

less water vapour diffuse out through stomata


Extension

• relative humidity the concentration gradient of water vapour between the air space and the atmosphere


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4 Air movement

rate

of

tran

spir

atio

n

wind velocity

rate of diffusion


Extension

• air movement the concentration gradient of water vapour between the leaf and the drier air outside


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Brief RevisionBrief Revision

1 The rate of transpiration can be measured with an apparatus called _________.potometer

2 Terrestrial dicotyledonous plants usually have more / less stomata on the upper epidermis than the lower epidermis.

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3 An increase in light intensity will increase / decrease the rate of transpiration.

4 An increase in relative humidity will increase / decrease the rate of transpiration.

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10.2 How are water and minerals absorbed in the roots?

Structure of the rootroot cap

• protects the tip of the root

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Structure of the root

epidermis

• made up of thin-walled cells

• protects the inner tissues from diseases

• not covered by cuticle

• has many root hairs

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root hair

• provides a large surface area for water absorption

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cortex• consists of several layers of

thin-walled cells

• stores starch

• allows the passage of water and minerals across the root

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vascular bundle ( 維管束 )• transports materials into and

out of the root

• made up of xylem (木質部 ) and phloem (韌皮部 ) tissues

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The adaptations of roots for absorption of water and minerals

1) Epidermal cells are not covered by cuticle and thus water can easily pass into them.

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2) Numerous root branches and root hairs provide a large surface area for absorption of water and minerals.

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3) The root hairs are long, fine structures.

easily grow between the soil particles

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10.6Examination of the structure of roots

Procedure:1 Examine the external structures of the root with a hand len

s. Draw a labelled diagram.

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10.6Examination of the structure of roots

Procedure:2 Examine the slide of the transv

erse section of the root with a microscope.

3 Identify the internal structures of the root. Draw a labelled diagram.

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Absorption of water in roots

1 Water moves into the root hairs by osmosis.

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2a Water moves into the neighbouring cortex cells by osmosis. it moves inwards

from cell to cell

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2b Some water moves along the cell wall.

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3 Water is drawn up the xylem vessel by transpiration pull.

xylem vessel in the stem

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4 Water evaporates from the leaf cells and diffuses out through the stomata as water vapour.

water vapour

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Absorption of minerals in the roots

Mineral salts dissolve in soil water to form ions (離子 ).

salts

ions

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Ions are absorbed into the roots by active transport, using energy from respiration.

salts

ions

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salts

ions

Some minerals are also absorbed in this way by diffusion.

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1 ____ ____ serves to protect the tip of the root.Root cap

2 _______ ______ consisting of xylem and phloem, serves to transport materials in and out of the root.

Vascular bundle

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4 Minerals can be absorbed by plants through osmosis / active transport / diffusion.

3 Root cells absorb water through osmosis / active transport / diffusion.

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10.3 How are water, minerals and organic nutrients transported inside plants?

Transport in flowering plants is provided by the vascular tissues.

xylem phloem

Patterns (分佈 ) in the roots, stems and leaves are different.

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leaf vein mid-rib vein

xylem

phloem

LEAF

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STEM phloem

xylem

pith (髓 )

cortex

epidermis

xylem

phloem


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ROOTphloem

xylem

cortex

epidermis

xylem

phloem


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10.7Examination of the vascular tissues in a young dicotyledonous stem

Procedure:1 Examine the slide of the tra

nsverse section of a young dicotyledonous stem with a microscope.

2 Identify the vascular tissues.

3 Draw a labelled diagram.

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Xylem• mainly consists of

xylem vessels


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Xylem3 characteristics:

1) Thick cell wall• contains cellulose (纖維素 ) and

lignin (木質素 )

• provides support to the plant


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Xylem2) Continuous hollow tube

• does not have cytoplasm or nuclei

3 characteristics:


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Xylem3) No end wall between cells

3 characteristics:


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Phloem3 components:

1) sieve plate (篩板 )• the end wall between cells

• has holes for dissolved substances to pass through


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Phloem3 components:

2) sieve tube (篩管 )• living cylindrical cells contain

cytoplasm but no nucleus

• cell wall is thin and does not contain lignin


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Phloem3 components:

3) companion cell (伴細胞 )• found alongside each sieve tube

• supports metabolism of sieve tubes

• contains cytoplasm and a nucleus


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Transport of water and minerals

Water and minerals are transported in xylem vessels.

driven by transpiration pull

Transpiration pull is the suctional force generated by transpiration.

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10.8Investigation of the plant tissue responsible for water transport

Procedure:1 Immerse the roots of a herbac

eous plant in dilute eosin solution for about 6 hours.

2 Cut transverse sections of the root, stem and leaf. Examine them with a microscope. Identify the tissue(s) with red colour.

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Transport of organic nutrients

Organic nutrients are transported in phloem in 2 ways.

up or down to the growing points for development

down to the roots or other storage organs

The process is called translocation (輸導作用 )

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Summary for the transport of water, minerals and organic nutrients in a plant



1 Water and minerals are absorbed into the roots.

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2 Water and minerals move up to other parts of the plant.


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3a Water and minerals are used for metabolism.

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3b Water is lost in transpiration.

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1 Organic nutrients are made in photosynthesis.


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2a Organic nutrients move down to growing fruit and roots for storage.


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2b Organic nutrients move up to the bud for growth and development.


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Brief RevisionBrief Revision1 Identify the following structures:

This is a transverse section of _ _ _ _ .

________xylem

________phloem________cortex

s t e m

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Brief RevisionBrief Revision2 The process which organic nutrients ar

e transported throughout the plants is called ___________ .translocation

3 ______ is the main tissue which transports water in the plant, while _______ is responsible for the transport of organic nutrients.

Xylem

phloem

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10.4 How are plants supported?

Plants are supported in two ways:

1) Turgidity of thin-walled cells

2) Hardness of thick-walled cells

Extension

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10.4 How are plants supported?Turgidity of thin-walled cellsTurgidity of thin-walled cells

Extension

In a condition of water supply:adequate

• water moves in by osmosis

press against each other

the cells become turgid

plant stands upright

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10.4 How are plants supported?Turgidity of thin-walled cellsTurgidity of thin-walled cells

Extension

In a condition of water supply:inadequate

• the cells will be plasmolysed

cannot press against each other

become flaccid

plant wilts (凋謝 )

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10.4 How are plants supported?Extension

Hardness of thick-walled cellsHardness of thick-walled cells

Xylem vessels

contain lignin, which makes them hard

provide mechanical support to the plants

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10.4 How are plants supported?Extension

Hardness of thick-walled cellsHardness of thick-walled cellsAs a woody plant (木質植物 ) grows, more and more xylem is formed.

the older xylem tissues are pushed inwards and become wood

wood

mature xylem cell

new xylem cell

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Summary concept diagramSummary concept diagramabsorption takes place in

in

absorb water by

lose water in

Plants

absorb minerals by

gain support byroots

osmosis

diffusion active transport

transpiration

woody plantsyoung woody

stemsherbaceous

plants

in

E

E E

E

E

turgidity ofthin-walled cells

hardness ofthick-walled cells

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Summary concept diagramSummary concept diagram

creates

affected bytranspiration pull

transpiration

temperaturelight intensity

E E E E

Back to summary concept diagram

air movementrelative humidity

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Summary concept diagramSummary concept diagram

consist of

transport takes place in

Back to summary concept diagram

Plants

vascular tissues

xylem

xylem vesselstransports

mainly consists of

transport organic nutrients

water minerals

phloem

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