chapter 23 roots, stems and leaves “gardening in the classroom” page 578
TRANSCRIPT
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Chapter
23Roots, Stems and Leaves“Gardening in the Classroom”
Page 578
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23–1 Specialized Tissues in Plants
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The three principal organs of seed plants are roots, stems, and leaves.
These organs perform functions such as the transport of nutrients, protection, and coordination of plant activities.
Seed Plant Structure23-1 Introduction to Plants
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Roots:
• absorb water and dissolved nutrients.
• anchor plants in the ground.
• protect the plant from harmful soil
bacteria and fungi.
Seed Plant Structure23-1 Introduction to Plants
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Stems:
• a support system for the plant body.
• a transport system that carries nutrients.
• a defense system that protects the plant
against predators and disease.
Seed Plant Structure23-1 Introduction to Plants
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Leaves:
• are a plant’s main photosynthetic systems.
• increase the amount of sunlight plants absorb.
Adjustable pores conserve water and let oxygen and
carbon dioxide enter leave.
Seed Plant Structure23-1 Introduction to Plants
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Plants consist of three main tissue systems:
•dermal tissue - outer
•vascular tissue - transport
•ground tissue - structure
Plant Tissue Systems23-1 Introduction to Plants
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Leaf
Stem
Root
Seed Plant Structure23-1 Introduction to Plants
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Dermal Tissue
Dermal tissue is the outer covering of a plant and consists of epidermal cells.
23-1 Introduction to Plants
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Vascular Tissue
Vascular tissue forms a transport system that contains several types of specialized cells.
•Xylem consists of tracheids and vessel elements.
•Phloem consists of sieve tube elements and companion cells.
23-1 Introduction to Plants
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Vascular Tissue
Xylem Phloem
Tracheid
Vessel element
Companion cell
Sieve tube element
Cross Section of a Stem
23-1 Introduction to Plants
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Vascular Tissue
Xylem
All seed plants have tracheids.
Tracheids are long, narrow cells that are
impermeable to water, but they have holes that connect cells.
Tracheid
Vessel element
23-1 Introduction to Plants
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Vascular Tissue
Angiosperms also have vessel
elements.
Vessel elements form a
continuous tube through which
water can move.
Tracheid
Vessel element
23-1 Introduction to Plants
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Vascular Tissue
Phloem
Phloem contains sieve tube elements and companion cells.
Sieve tube elements are phloem cells
joined end-to-end to form sieve
tubes.
Sieve tube element
Companion cell
23-1 Introduction to Plants
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Vascular Tissue
The end walls of sieve tube
elements have many small holes that
sugars and other foods can move through.
Companion cell
Sieve tube element
23-1 Introduction to Plants
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Vascular Tissue
Companion cells are phloem cells that
surround sieve tube elements.
Companion cells support sieve tubes
and aid in the movement of
substances in and out of the phloem.
Sieve tube element
Companion cell
23-1 Introduction to Plants
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Between dermal and vascular tissues are ground tissues.
Three kinds of ground tissue:
•Parenchyma- thin walls and large central vacuoles – storage (fruit)
•Collenchyma- strong, flexible cell walls that help support larger plants (celery)
•Sclerenchyma- extremely thick, rigid cell walls = tough and strong (wood)
23-1 Introduction to Plants Ground Tissue
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23-1 Introduction to Plants Ground Tissue
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Growth & Meristematic Tissue
In most plants, new cells are produced at the tips of the roots and stems.
These cells are produced in meristems.
Meristematic tissue is the only plant tissue that produces new cells by mitosis.
A meristem is a cluster of tissue that is responsible for continuing growth throughout a plant's lifetime.
23-1 Introduction to Plants
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Near the tip of each growing stem and root is an apical meristem.
Growth & Meristematic Tissue23-1 Introduction to Plants
An apical meristem is at the tip of a
growing stem or
root.
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23–2 Roots
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In some plants, the primary root grows long and thick and is called a taproot.
Fibrous roots branch to such an extent that no single root grows larger than the rest.
Types of Roots
23-2 Roots
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Fibrous Roots
Types of Roots23-2 Roots
Tap Roots
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Fibrous Roots
Types of Roots23-2 Roots
A carrot is an example of a taproot.
Tap Roots
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Fibrous Roots
Types of Roots23-2 Roots
Fibrous roots are found in grasses.
Tap Roots
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Root Structure and Growth
•Roots contain cells from dermal, vascular, and ground tissue.
23-2 Roots
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A mature root has an outside layer, the epidermis, and a central cylinder of vascular tissue.
Between these two tissues lies a large area of ground tissue.
The root system plays a key role in water and mineral transport.
Root Structure and Growth23-2 Roots
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The root’s surface is covered with cellular
projections called root hairs.
Root hairs provide a large surface area
through which water can enter the plant.
Root hairs
Root Structure and Growth23-2 Roots
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The epidermis (including root hairs) protects
the root and absorbs water.
Epidermis
Root Structure and Growth23-2 Roots
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Inside the epidermis is a
layer of ground tissue called the
cortex.
Ground tissue (cortex)
Root Structure and Growth23-2 Roots
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The cortex extends to another layer of
cells, the endodermis.
The endodermis completely
encloses the vascular cylinder.
Endodermis
Root Structure and Growth23-2 Roots
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The vascular cylinder is the central region of a root that includes the xylem and phloem.
Vascular cylinder
Phloem
Xylem
Root Structure and Growth23-2 Roots
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Roots grow in length as their
apical meristem produces new cells
near the root tip.
Apical meristem
Root Structure and Growth23-2 Roots
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These new cells are covered by
the root cap that protects the
root as it forces its way through
the soil.Root cap
Apical meristem
Root Structure and Growth23-2 Roots
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Root Functions
The most important nutrients plants need include:
•nitrogen
•phosphorus
•potassium
•magnesium
•calcium
23-2 Roots
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Root Functions
Active Transport of Minerals
•The cell membranes of root epidermal cells contain active transport proteins.
23-2 Roots
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Root Functions
•Transport proteins use ATP to pump mineral ions from the soil into the plant.
Root hairs
23-2 Roots
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Root Functions
The high concentration of mineral ions in the plant cells causes water molecules to move into the plant by osmosis.
23-2 Roots
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Root Functions
Movement Into the Vascular Cylinder
•Osmosis and active transport move water and minerals from the root epidermis into the cortex.
•The water and dissolved minerals pass the inner boundary of the cortex and enter the endodermis.
23-2 Roots
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Root Functions
The endodermis is composed of many individual cells.
Endodermis
23-2 Roots
Water moves into the vascular cylinder
by osmosis.
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Root Functions
Each cell is surrounded on four sides by a waterproof strip called a Casparian strip.
Casparian strip
Casparian strip
23-2 Roots
The Casparian strip prevents the backflow of water out of
the vascular cylinder into the root cortex.
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Root Functions
As more water moves from the cortex into the vascular cylinder, more water in the xylem is forced upward through the root into the stem.
23-2 Roots
Root pressure pushes water through the
vascular system of the entire plant.
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23–3 Stems
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Stem functions:
•they produce leaves, branches and flowers
•they hold leaves up to the sunlight
•they transport substances between roots and leaves
•Can do photosynthesis
Stem Structure and Function23-3 Stems
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Stems make up an essential part of the water and mineral transport systems of the plant.
Xylem and phloem form continuous tubes from the roots through the stems to the leaves.
This allows water and nutrients to be carried throughout the plant.
Stem Structure and Function23-3 Stems
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Stems are surrounded by a layer of epidermal cells that have thick cell walls and a waxy protective coating.
Stem Structure and Function23-3 Stems
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•Leaves attach to the stem at structures called nodes.
•The regions of stem between the nodes are internodes.
•Small buds are found where leaves attach to nodes.
Node
Internode
Bud
Node
Stem Structure and Function23-3 Stems
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Buds contain undeveloped tissue
that can produce new stems and leaves.
In larger plants, stems develop woody
tissue that helps support leaves and
flowers.
Bud
Stem Structure and Function23-3 Stems
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Monocot
Vascular bundles
Epidermis
Ground tissue
Monocot and Dicot Stems23-3 Stems
Monocot Stems
•Monocot stems have a distinct
epidermis, which encloses
vascular bundles.
•Each vascular bundle contains
xylem and phloem tissue.
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•Monocot Stems
•Vascular bundles are
scattered throughout the ground tissue.
•Ground tissue consists mainly of parenchyma
cells.
Monocot
Vascular bundles
Epidermis
Ground tissue
Monocot and Dicot Stems23-3 Stems
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Dicot Stems
•Dicot stems have vascular
bundles arranged in a
ringlike pattern.
•The parenchyma
cells inside the vascular tissue are known as
pith.Dicot
Cortex
Pith
Vascular bundles Epidermis
Monocot and Dicot Stems23-3 Stems
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•Dicot Stems
•The parenchyma cells outside of
the vascular tissue form the
cortex of the stem.
Dicot
Cortex
Pith
Vascular bundles Epidermis
Monocot and Dicot Stems23-3 Stems
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Primary Growth of Stems•All seed plants
undergo primary growth,
which is an increase in
length.
•For the entire life of the plant, new
cells are produced at the tips of roots and
shoots.
Year 1Year 2
Year 3
Primary growth
Apical meristemPrimary growth
Leaf scar
23-3 Stems
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Primary growth of stems is produced by cell divisions in
the apical meristem. It takes place in all seed
plants.
Apical meristem
Primary Growth of Stems23-3 Stems
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Secondary Growth of Stems
Stems increase in width due to secondary growth.
Secondary growth produces wood.
Thin tree ring = slow growth, often due to drought.
23-3 Stems
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Formation of the Vascular Cambium
•Once secondary growth begins, the vascular cambium appears as a thin layer between the xylem and phloem of each vascular bundle.
Vascular cambium
Secondary Growth of Stems23-3 Stems
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The vascular cambium divides to produce xylem cells toward the center of the stem and phloem cells toward the outside.
Secondary xylem
Secondary phloem
Secondary Growth of Stems23-3 Stems
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Formation of Wood
•Wood is actually layers of xylem.
These cells build up year after year.
Wood Bark
Secondary Growth of Stems23-3 Stems
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As woody stems grow thicker, older
xylem cells near the center of the stem no longer conduct
water.
This is called heartwood.
Heartwood supports the tree.
Xylem: Heartwood
Secondary Growth of Stems23-3 Stems
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Heartwood is surrounded by
sapwood.
Sapwood is active in water and
mineral transport.
Xylem: Sapwood
Secondary Growth of Stems23-3 Stems
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Formation of Bark
•On most trees, bark includes all
of the tissues outside the
vascular cambium —
phloem, the cork cambium and
cork.
Bark
Secondary Growth of Stems23-3 Stems
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Secondary Growth of Stems
The vascular cambium
produces new xylem and
phloem, which increase the width
of the stem.
Vascular cambium
23-3 Stems
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Secondary Growth of Stems
The phloem transports
sugars produced by
photosynthesis.
Phloem
23-3 Stems
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The cork cambium
produces a protective
layer of cork.
Cork cambium
Secondary Growth of Stems23-3 Stems
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The cork contains old,
nonfunctioning phloem that protects the
tree.
Cork
Secondary Growth of Stems23-3 Stems
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23–4 Leaves
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Leaf Structure
The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.
23-4 Leaves
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Leaf Structure
To collect sunlight, most leaves have thin, flattened sections called blades.
Blade
Stem
Bud Petiole
Simple leaf
Compound leaf
Leaflet
23-4 Leaves
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Leaf Structure
The blade is attached to the stem by a thin stalk called a petiole.
Blade
Stem
Bud Petiole
Leaflet
23-4 Leaves
Simple leaf
Compound leaf
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Leaf Structure
Simple leaves have only one blade and one petiole.
Blade
Stem
Bud Petiole
Leaflet
23-4 Leaves
Simple leaf
Compound leaf
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Leaf Structure
Compound leaves have several blades, or leaflets, that are joined together and to the stem by several petioles.
Blade
Stem
Bud Petiole
Leaflet
23-4 Leaves
Simple leaf
Compound leaf
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Leaf Structure
Leaves are covered on the top and bottom by epidermis.
Epidermis
Epidermis
23-4 Leaves
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Leaf Structure
The epidermis of many leaves is covered by the cuticle.
Epidermis
Epidermis
Cuticle
23-4 Leaves
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Leaf Structure
The cuticle and epidermal cells form a waterproof barrier that protects tissues inside the leaf and limits the loss of water through evaporation.
The veins of leaves are connected directly to the vascular tissues of stems.
23-4 Leaves
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Leaf Structure
In leaves, xylem and phloem tissues are gathered together into bundles that run from the stem into the petiole.
In the leaf blade, the vascular bundles are surrounded by parenchyma and sclerenchyma cells.
23-4 Leaves
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Leaf Structure
All these tissues form the veins of a leaf.
Xylem Phloem Vein
23-4 Leaves
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Leaf Functions
•Most leaves consist of a specialized ground tissue known as mesophyll.
Palisade mesophyll
Spongy mesophyll
23-4 Leaves
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Leaf Functions
The layer of mesophyll cells found directly under the epidermis is called the palisade mesophyll. These closely-packed cells absorb light that enters the leaf.
Palisade mesophyll
23-4 Leaves
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Leaf Functions
Beneath the palisade mesophyll is the spongy mesophyll, a loose tissue with many air spaces between its cells.
Spongy mesophyll
23-4 Leaves
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Leaf Functions
The air spaces connect with the exterior through stomata.
Stomata are openings in the underside of the leaf that allow carbon dioxide and oxygen to diffuse in and out.
Stoma
23-4 Leaves
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Leaf Functions
Each stoma consists of two guard cells that
control the opening and
closing of stomata by responding to changes in water
pressure. Guard cells
23-4 Leaves
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Leaf Functions
Transpiration is the loss of water
through leaves.
Transpiration pulls water from the
roots through the vascular tissues
and out the leaves.
23-4 Leaves
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Leaf Functions
When water pressure within guard cells is high, the stoma open.
23-4 Leaves
Stoma are open in daytime,
when photo -synthesis is active.
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Leaf Functions
When water pressure within guard cells decreases, the stoma closes.
23-4 Leaves
Stomata are closed at night, to
prevent water loss.
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23–5 Transport in Plants
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Water Pressure
•Xylem tissue forms a continuous set of tubes that runs from the roots through stems and out into the spongy mesophyll of leaves.
•Active transport and root pressure cause water to move from soil into plant roots.
•Capillary action and transpiration also are needed to transport water and minerals.
23-5 Transport in Plants
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Water Pressure
The combination of root pressure, capillary action, and transpiration provides enough force to move water through the xylem tissue of even the tallest plant.
23-5 Transport in Plants
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Water Pressure
Cohesion is the attraction of water molecules to each other.
23-5 Transport in Plants
Adhesion is the attraction between unlike molecules.
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Water Pressure
The tendency of water to rise in a thin
tube is called capillary action.
Water is attracted to the walls of the tube, and water molecules are attracted to one
another.
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Water Pressure
Capillary action causes water to
move much higher in a
narrow tube than in a wide tube.
23-5 Transport in Plants
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Water Pressure
Tracheids and vessel elements form hollow connected tubes in a plant.
Capillary action in xylem causes water to rise well above the level of the ground.
23-5 Transport in Plants
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Water Pressure
•When water is lost through
transpiration, osmotic pressure moves water out of the vascular
tissue of the leaf.
23-5 Transport in Plants
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Water Pressure
The movement of water out of the leaf
“pulls” water upward through the vascular system all
the way from the roots.
This process is known as
transpirational pull.
23-5 Transport in Plants
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Water Pressure
Controlling Transpiration
•The water content of the leaf is kept relatively constant.
•When there is a lot of water, water pressure in the guard cells is increased and the stomata open.
•Excess water is lost through open stomata by transpiration.
23-5 Transport in Plants
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Nutrient Transport
•Many plants pump sugars into their fruits.
• In cold climates, plants pump food into their roots for winter storage.
•This stored food must be moved back into the trunk and branches of the plant before growth begins again in the spring.
23-5 Transport in Plants
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Nutrient Transport
Movement from Source to Sink
•A process of phloem transport moves sugars through a plant from a source to a sink.
•A source is any cell in which sugars are produced by photosynthesis.
•A sink is any cell where the sugars are used or stored.
23-5 Transport in Plants
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Nutrient Transport23-5 Transport in Plants
The pressure-flow hypothesis explains how phloem transport takes
place.
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Sugars produced during
photosynthesis are pumped into the phloem (source).
Sugar molecules
Movement of water
Movement of sugar
Phloem Xylem
Source cell
Nutrient Transport23-5 Transport in Plants
Pressure-Flow Hypothesis
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As sugar concentrations increase in the
phloem, water from the xylem moves in
by osmosis.
Movement of water
Movement of sugar
Sugar molecules
Phloem Xylem
Source cell
Nutrient Transport23-5 Transport in Plants
Pressure-Flow Hypothesis
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Movement of water
Movement of sugar
This movement causes an increase in
pressure at that point, forcing
nutrient-rich fluid to move through the
phloem from nutrient-producing regions ….
Sugar molecules
Phloem Xylem
Source cell
Nutrient Transport23-5 Transport in Plants
Pressure-Flow Hypothesis
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…. toward a region that uses these nutrients
(sink).
Xylem Phloem
Movement of water
Movement of sugar
Sink cell
Nutrient Transport23-5 Transport in Plants
Pressure-Flow Hypothesis
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If part of a plant actively absorbs
nutrients from the phloem, osmosis
causes water to follow.
Movement of water
Movement of sugar
Xylem Phloem Sink cell
Nutrient Transport23-5 Transport in Plants
Pressure-Flow Hypothesis
This decreases pressure and causes a movement
of fluid in the phloem toward the sink.