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Chapter 18
Transport in the Flowering Plant
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Plants are AutotrophicPlants are Autotrophic, they , they make their own make their own food during Photosynthesis in the leaves.food during Photosynthesis in the leaves.
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To provide the materials needed for various plant metabolic processes including Photosynthesis, Respiration , Growth and Reproduction
Why do plants need a transport system?
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What materials are transported in plants
1. Water
2. Carbon dioxide
3. Minerals
4. Carbohydrates produced in photosynthesis
5. Plant growth regulators
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Water uptake Root epidermal cells absorb water by osmosis.
Adaptations for absorption:
1.Root hairs give a large surface area
2.Have thin walls
3.Don’t have a waxy cuticle
4.The cell sap has a lower water concentration than soil water
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Root Hair
Ground tissue
Xylem
Water
Xylem form continuous hollow pipes from roots to leaf
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Water uptake
Water movement through the root Water moves from
1.the epidermal cells across
2.the ground tissue of the cortex and into
3.the xylem vessels.
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Giant RedwoodsGiant RedwoodsThe largest and oldest trees in the worldThe largest and oldest trees in the world
A single mature giant redwood can draw A single mature giant redwood can draw 650,000 litres of water up through it in one 650,000 litres of water up through it in one season!season!
How is this possible?How is this possible?
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Upward movement of water Two mechanisms combine to cause upward movement of water through the stem in the xylem.
They form a continuous hollow pipeline from the roots to the leaves.
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1. Root pressure – When water is drawn into roots by osmosis the extra volume causes pressure to build up. This pressure pushes water up through the xylem
Root Pressure 13
2. Transpiration - the loss of water vapour from the plant. As water evaporates from the leaf, more water is pulled upwards through the xylem into the leaf.
Transpiration
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Role of Transpiration Water evaporates from the leaf cells during transpiration – 99%.The cells become less turgid. The evaporation of water from the leaf cells causes more water to be pulled upwards as a contionus column to replace it through the xylem vessels.
Animation of Transpiration stream
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Learning check 11.Define Autotroph.
2.Why do plants need a transport system?
3.What materials are transported in plants?
4.How are root hairs are adapted to the process of absorbing water?
5.Outline the pathway taken by water into the plant.
6.Name the two mechanisms combined to cause the upward movement of water through the stem in the xylem
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The control of TranspirationThe control of TranspirationLeaves need to replace the water they lose in Leaves need to replace the water they lose in transpiration or they may wilt and die.transpiration or they may wilt and die.
To prevent wilting plants need to control how To prevent wilting plants need to control how much water they lose in transpiration.much water they lose in transpiration.
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1. Presence or absence of a cuticleLeaves have a waxy cuticle through which
water cannot pass – this is mainly on the upper side of a leaf as this side is more exposed and more water can evaporate here.
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2. Opening and closing of the stomataOpenings on the lower epidermis of leaves for gas exchange.Guard cells control the opening - increases water loss and the closing - reduces water loss of the Stomata.
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Structure and working of Stomata
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Summary of Transpiration
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When are stomata open and closed?When are stomata open and closed?• Stomata open during the day when
photosynthesis is taking place to allow water vapour out and CO2 in.
• Stomata close at night reducing water loss and CO2 intake as photosynthesis is not occurring.
Animations showing movement of water during transpiration
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Conditions when stomata close at dayConditions when stomata close at dayTwo reasons stomata may close during the day:
1.If the plant has lost too much water
2.If temperatures are too high
By closing stomata the plant reduces water loss.
In dry conditions stomata remain closed for long periods, photosynthesis cannot occur and food crops are reduced.
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Learning Check 2Learning Check 2
1.1. What is Transpiration?What is Transpiration?
2.2. Explain the role of Transpiration in water transport.Explain the role of Transpiration in water transport.
3.3. What controls Transpiration? What controls Transpiration?
4.4. What controls the loss of water from leaf? What controls the loss of water from leaf?
5.5. 3 Methods of controlling transpiration are?3 Methods of controlling transpiration are?
6.6. When are stomata open and closed?When are stomata open and closed?
7.7. Explain the role of Root pressure in water transport.Explain the role of Root pressure in water transport.
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Cohesion-Tension Model of Xylem Transport
Need to KnowNeed to Know1. How plants move water up to great heights
against the force of gravity2. Know the contribution of Irish scientists
Dixon and Joly to plant biology3. Understand the terms transpiration,
cohesion, adhesion, tension, osmosis and use them to explain water movement up through xylem
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Cohesion-Tension Model of Xylem Transport:
explains how water is transported in plants to extreme heights against the force of gravity.
Cohesion-Tension Model of Xylem Transport
Henry Dixon
Working in Trinity College 1894
Theory proposed by two Irish scientists
John Joly
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The cohesion-tension model of The cohesion-tension model of water transport in xylemwater transport in xylem
• Two Irish Scientists working in Trinity College Two Irish Scientists working in Trinity College Henry Dixon and John Joly put forward this Henry Dixon and John Joly put forward this model in 1894model in 1894
• CohesionCohesion – the sticking of similar molecules to – the sticking of similar molecules to each other, water molecules stick to each othereach other, water molecules stick to each other
• Adhesion Adhesion – when different molecules stick – when different molecules stick together, water adheres to the walls of xylem together, water adheres to the walls of xylem but this force is not as great as the cohesive but this force is not as great as the cohesive forces of waterforces of water
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Similar molecules sticking together e.g. water sticking to water
Cohesion
Attraction between molecules
H
HO
H
HO
H
HO
H
HO
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CohesionCohesion
Animation showing Cohesion by hydrogen bonding in water
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Different molecules sticking together e.g. water sticking to xylem walls
Adhesion
Attraction
H
HO
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The Cohesion – Tension model 1. Cohesion between water
molecules in the narrow xylem tubes causes the water to form into a continuous column or stream in the xylem
H2O
H2O
H2O
H2O
H2O
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2. Water molecules evaporate due to transpiration at the leaf.
•Cohesion between the water molecules replaces the water by pulling the next water molecule up the xylem.
•As the column of water is hard to break this pull is felt down the entire column of water to the root.
H2O
H2O
H2O
H2O
H2O
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As each water molecule is “pulled” from the xylem another water molecule is “pulled” up from the root.
This pulling force is passed from water molecule to water molecule all the way down the plant.
This is how water is pulled up through the plant by transpiration.
Animations of Cohesion-tension43
3. Transpiration from the leaf
•Puts the column of water under tension•Tension can pull a column of water to great heights in plants•Tension causes the column of water to be stretched•But the cohesive forces between the water molecules are strong enough to prevent the column breaking•The strong lignin prevents xylem vessels collapsing inward
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View An Animation of sugar and water moving through View An Animation of sugar and water moving through xylem and phloemxylem and phloem
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Outline of cohesion tension modelOutline of cohesion tension model
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Summary pointsSummary points1. Water evaporates from the leaf, as each
water molecule evaporates another is pulled up through the thin xylem column
2. This pulling of water molecules puts all the water in the xylem vessels under tension
3. This tension is great enough to pull water to a height of 150m
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Summary pointsSummary points4. Stomata open in daylight and transpiration
occurs causing xylem vessels to become narrow, stems therefore are narrower at day
5. The strong lignin prevents xylem vessels collapsing inward
6. When transpiration stops (at night) the tension is released and xylem vessels return to their normal width
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Learning Check 3Learning Check 3
1. Explain the terms Cohesion, Adhesion, Transpiration, Tension, Osmosis
2. Name the Irish scientists who proposed the tension cohesion model of water movement.
3. Explain how plants move water to great heights against the force of gravity.
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Mineral uptake and transportMineral uptake and transport
Examples
Calcium ……
Magnesium …..
Nitrates
Phosphates
Potassium
Helps make cell walls
Part of chlorophyll
Are transported from the roots in the xylem, dissolved in water
Are absorbed by active transport which requires energy
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Uptake & transport of Carbon dioxideUptake & transport of Carbon dioxide• Most of the Carbon dioxide comes in through Most of the Carbon dioxide comes in through
the stomata from the atmospherethe stomata from the atmosphere
• It diffuses into the air spaces and then into It diffuses into the air spaces and then into the photosynthesising cells in the ground the photosynthesising cells in the ground tissuetissue
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Carbon Dioxide SourcesCarbon Dioxide Sources1. Produced in the leaf during respiration
2. Diffuses from the air in though the stomata
CO2
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Photosynthesis ProductsPhotosynthesis Products
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Glucose•Glucose is converted to starch•Starch and glucose are transported in the PhloemOxygen•Some diffuses into air spaces in the leaf and out through stomata into the atmosphere•some of the oxygen produced is needed for respiration
• Glucose is the carbohydrate made in photosynthesis
• This may be used immediately for energy for the plant in respiration or it may be stored as starch
• Some of this starch is stored in the spongy mesophyll cells in leaves
• Starch stored in leaves is important in the diet of leaf eating animals such as horses and cattle
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Trans-section of a leafTrans-section of a leaf
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Glucose converted to sucroseGlucose converted to sucrose• When glucose get converted to sucrose it
enters phloem sieve tubes and is transported through the plant
• This sugary water is called phloem sap
An insect extracting sugary phloem sap from a plant
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Food transportFood transport
• Phloem carries food to all parts of the plant, some food is sent to growth areas such as buds, flowers and roots.
• Food is used to form new plant structures, for respiration or it is stored as starch.
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Learning Check 4Learning Check 41. Name 4 Minerals taken up by the plant.
2. How are they transported?
3. Describe the uptake and transport of Carbon dioxide.
4. List the Products of Photosynthesis & state their use
5. What is the function of the phloem?
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Food storage organs in plantsFood storage organs in plants
• Some parts of plants may become swollen and fleshy with stored food
• This food will be used by the plant to produce flowers, seeds and fruits
Modified RootModified RootE.g. Tap roots of Carrots, turnips, sugar beetE.g. Tap roots of Carrots, turnips, sugar beet
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Modified stemModified stem• Potato plants develop an underground stem Potato plants develop an underground stem
systemsystem
• The tips become swollen with stored starchThe tips become swollen with stored starch
• These swollen tips are called stem These swollen tips are called stem tuberstubers
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Modified LeavesModified LeavesE.g. onion bulbs , daffodils bulbsE.g. onion bulbs , daffodils bulbs and tulips bulbsand tulips bulbs
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• A bulb contains a tiny underground stem which have swollen fleshy leaves attached
• This stem has an apical bud and lateral buds can be seen where the leaves meet the reduced stem
• The entire bulb is protected by dry scaly leaves
• Some bulbs are edible (onion, garlic) while others are poisonous (daffodil, tulip) this prevents organisms in the soil from eating them!
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Modified PetiolesModified Petioles• Celery and Rhubarb are modified petiolesCelery and Rhubarb are modified petioles
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Learning Check 5Learning Check 5
1.1. Name 4 food storage organs in plants.Name 4 food storage organs in plants.
2.2. What is the function of the stored food?What is the function of the stored food?
3.3. What are Potato plants?What are Potato plants?
4.4. Describe the structure of a bulb.Describe the structure of a bulb.
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Websites on storage organs in Websites on storage organs in plants & Transpirationplants & Transpiration
http://theseedsite.co.uk/bulbs.html http://theseedsite.co.uk/bulbs.html
http://www.cactus-art.biz/note-book/Dictionary/Dictionary_S/http://www.cactus-art.biz/note-book/Dictionary/Dictionary_S/dictionary_storage_organ.htm dictionary_storage_organ.htm
http://youtu.be/fNtFwQ4NpDghttp://youtu.be/fNtFwQ4NpDg
Told in storybook fashion, this short film narrates the struggle of Told in storybook fashion, this short film narrates the struggle of one water droplet, Vladimir, who faces the bourgeoisie-promoted one water droplet, Vladimir, who faces the bourgeoisie-promoted process of transpiration.process of transpiration.
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