Download 17.3 What Are The Tissues And Cell Types Of Plants?

Chapter 17
Plant Form
and Function
Lectures by
Gregory Ahearn
University of North Florida
Copyright © 2009 Pearson Education, Inc..
17.1 How Are Plant Bodies Organized?
 Flowering plants have a root system and a
shoot system.
• Flowering plant bodies consist of two major
parts: the root system and the shoot system.
• Roots are branched portions of the plant body
that are usually embedded in soil and serve to
anchor the plant and absorb water and
nutrients from the soil.
Copyright © 2009 Pearson Education Inc.
17.1 How Are Plant Bodies Organized?
 Flowering plants have a root system and a
shoot system (continued).
• The part of the plant above ground is the
shoot system, and consists of leaves, buds,
flowers, and fruit born on stems.
• The functions of shoots include
photosynthesis, reproduction, and transport
between different parts of the plant body.
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apical meristem
beginning
leaves
terminal bud
flower
stem
leaf
lateral bud
Shoot system
branch
tap root
Root system
branch roots
root hairs
root cap
Fig. 17-1
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17.1 How Are Plant Bodies Organized?
 Flowering plants can be divided into two
groups:
• The monocots, which include the grasses,
lilies, palms, and orchids
• The dicots, which include deciduous trees
(those that drop their leaves in winter),
bushes, and many garden flowers
Copyright © 2009 Pearson Education Inc.
17.1 How Are Plant Bodies Organized?
Leaves
Stems
Roots
Monocots
Flowers
Seeds
embryo
cotyledon
Flower parts are in
threes or multiples
of three
Leaves have smooth
edges, often narrow,
with parallel veins
Vascular bundles
are scattered
throughout the stem
Monocots have a
fibrous root system
The seed has one
cotyledon (seed leaf)
Dicots
embryo
Flower parts are in
fours or fives or multiples
of four or five
cotyledons
Leaves are palmate
(handlike) or oval
with netlike veins
Vascular bundles
are arranged in a
ring around the stem
Dicots have a
taproot system
The seed has
two cotyledons
(seed leaves)
Fig. 17-2
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17.2 How Do Plants Grow?
 During growth, meristem cells give rise to
differentiated cells.
• Plant bodies are composites of two
fundamentally different kinds of cells:
meristem and differentiated cells.
• Meristem cells are capable of mitosis.
• Some meristem cells stop dividing and
become permanent, non-mitotic differentiated
cells.
• Differentiated cells become mature leaves or
trunks of trees.
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17.2 How Do Plants Grow?
 During growth, meristem cells give rise to
differentiated cells (continued).
• Plants grow by cell division of two types of
meristem cells:
• Apical meristem, at tips of roots and shoots
• Lateral meristem, also called cambia, form
cylinders that run lengthwise inside roots
and stems
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17.2 How Do Plants Grow?
 Different processes are responsible for
growth in length and width.
• Primary growth occurs by division of apical
meristem cells, and leads to growth in length
at the tips of roots and shoots.
• Secondary growth occurs by mitotic division of
lateral meristem cells, and increases the
thickness of the stems and roots as they age.
Copyright © 2009 Pearson Education Inc.
17.3 What Are The Tissues And Cell Types
Of Plants?
 The structures of plants consist of three
types of plant tissues:
• Dermal tissue, which covers the outer
surfaces of the plant body
• Ground, nondermal, nonvascular tissue that
makes up most of the body of young plants
• Vascular tissue, which transports water,
nutrients, and sugars throughout the plant
Copyright © 2009 Pearson Education Inc.
ground tissue
dermal
tissue
system
vascular
tissue
system
ground
tissue
system
vascular
tissue
system
Root system
vascular tissue
Shoot system
17.3 What Are The Tissues And Cell Types
Of Plants?
 The structure of
the root and
shoot
Fig. 17-3
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17.3 What Are The Tissues And Cell Types
Of Plants?
 Dermal tissue covers the plant body.
• The outermost covering on leaves, stems, and
roots of all young plants is part of the dermis
called the epidermis.
• This part of the plant is covered by a
waterproof layer known as a cuticle, which
reduces evaporation of water from the plant.
• Roots have no cuticle because it would
prevent the absorption of water and nutrients
from the soil.
• Epidermal cells are replaced by cork cells as
the plant ages.
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17.3 What Are The Tissues And Cell Types
Of Plants?
 Dermal tissues cover plant surfaces.
stomata
leaf hair
Fig. 17-4
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17.3 What Are The Tissues And Cell Types
Of Plants?
 Ground tissue makes up most of the young
plant body.
• Ground tissue cells typically carry out most of
the metabolic activities of the plant.
• These tissues may photosynthesize, store
sugars and starches, or secrete hormones.
• Roots of plants, like carrots and sweet
potatoes, are packed with ground tissue that
stores carbohydrates such as starch and
sugar.
• Ground tissue also provides support in stems
such as celery stalks.
Copyright © 2009 Pearson Education Inc.
17.3 What Are The Tissues And Cell Types
Of Plants?
 Vascular tissue consists of xylem and
phloem.
• Vascular tissue occurs in strands, called
vascular bundles, that contain both xylem and
phloem.
Copyright © 2009 Pearson Education Inc.
17.3 What Are The Tissues And Cell Types
Of Plants?
 Xylem conducts water and dissolved
nutrients from the roots to the rest of the
plant.
• Xylem tissues are called tracheids and vessel
elements.
• Tracheids are thin in diameter, while the
vessel elements are wider and provide a
relatively unobstructed pipeline from root to
leaf.
Copyright © 2009 Pearson Education Inc.
17.3 What Are The Tissues And Cell Types
Of Plants?
 Xylem
ground tissue
cells (fibers)
pits
Pits link the insides
of the tracheids and
vessel elements
Openings connect
the vessel elements
end
wall
tracheids
vessel
element
(a) Xylem structure
tracheids
vessel
element
(b) Longitudinal section of xylem
Fig. 17-5
Copyright © 2009 Pearson Education Inc.
17.3 What Are The Tissues And Cell Types
Of Plants?
 Phloem conducts substances throughout
the plant.
• Substances that are synthesized by the
plant—such as sugars, amino acids, and
hormones—are conducted through the plant
by phloem.
• Phloem has sieve tubes that form continuous
conducting tubes that connect all parts of the
plant.
Copyright © 2009 Pearson Education Inc.
17.3 What Are The Tissues And Cell Types
Of Plants?
 Phloem
ground
tissue
cells
Sieve plates connect
the sieve-tube elements
sieve plate
with pores
sieve-tube
element
companion
cell
nucleus
(a) Phloem structure
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companion
cell
(b) Cross section of phloem
Fig. 17-6
17.4 How Do Roots Grow And What Do
They Do?
 Dicots and monocots have different types of
roots.
• Dicots, such as carrots and dandelions, have
a single taproot with smaller side roots.
• Monocots, like grasses and palms, have
numerous roots at the base of the plant that
are the same size, called fibrous roots.
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17.4 How Do Roots Grow And What Do
They Do?
 Taproots and fibrous roots
Fig. 17-7
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17.4 How Do Roots Grow And What Do
They Do?
 Roots elongate by primary growth.
• In young roots, divisions of the apical
meristem give rise to four distinct regions:
• An outer envelop of epidermis
• A vascular cylinder at the core of the root
• A cortex between the two
• A protective root cap at the tip of the root
that protects the apical meristem from being
scraped off as the root pushes downward
Copyright © 2009 Pearson Education Inc.
17.4 How Do Roots Grow And What Do
They Do?
epidermis
root hair
cortex
endodermis
of cortex
xylem
phloem
vascular
cylinder
apical
meristem
root
cap
Fig. 17-8
Copyright © 2009 Pearson Education Inc.
17.4 How Do Roots Grow And What Do
They Do?
 The epidermis of the root is very permeable
to water.
• The root’s outermost covering of cells is the
epidermis, which contacts the soil and any air
or water trapped among the soil particles.
• The cell walls of epidermal cells are highly
water permeable, allowing water to penetrate
into the interior of the root.
Copyright © 2009 Pearson Education Inc.
17.4 How Do Roots Grow And What Do
They Do?
 Many epidermal cells have root hairs, which
are long, thin extensions that grow into the
surrounding
soil and
increase
the roots
ability to
root
hairs
absorb
water and
nutrients.
Fig. 17-9
Copyright © 2009 Pearson Education Inc.
17.4 How Do Roots Grow And What Do
They Do?
 The cortex controls the absorption of water
and nutrients.
• Cortex is a type of ground tissue that makes
up most of the inside of a young root.
• The cortex consists of an outer mass of large,
loosely packed cells just beneath the
epidermis, and an inner layer of smaller,
close-fitting cells called the endodermis, which
encircles the vascular cylinder.
Copyright © 2009 Pearson Education Inc.
17.4 How Do Roots Grow And What Do
They Do?
 The cortex controls the absorption of water
and nutrients (continued).
• Water and nutrients move from the cortex into
the vascular cylinder by moving across the
membranes of the endodermal cells, which
regulate the types and amounts of materials
that the roots absorb.
Copyright © 2009 Pearson Education Inc.
17.4 How Do Roots Grow And What Do
They Do?
 The vascular cylinder contains xylem and
phloem, and meristem for branch roots.
• The vascular cylinder of a root contains the
conducting tissues of xylem and phloem,
which transport water and dissolved materials
within the plant.
• The outermost layer of the vascular cylinder
retains the ability to divide and form the apical
meristem of new roots that grow as branches
from existing roots.
Copyright © 2009 Pearson Education Inc.
17.4 How Do Roots Grow And What Do
They Do?
 A new branch root breaks out through the
cortex and epidermis of the primary root by
secreting enzymes that digest them away.
 The vascular tissues of the branch root
connect with the vascular tissues of the
primary root.
Fig. 17-10
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17.5 How Do Stems Grow And What Do
They Do?
 Stems grow in length by the mitotic apical
stem cells of the terminal bud.
• The apical meristem differentiates into four
specialized cell types: stem cells, bud cells,
leaf cells, and flower cells.
• Young stems are composed of four tissues:
• Epidermis (dermal tissue)
• Cortex (ground tissue)
• Pith (ground tissue)
• Vascular tissue
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terminal bud
beginning leaves
apical
meristem
sunflower
(dicot)
stem
pith
node
lateral bud
epidermis
internode
blade
stalk
branch
(sprouted
lateral bud)
vascular cortex
bundle
leaf
pith
epidermis
pith
vascular
bundle
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cortex
phloem
vascular
cambium
xylem
phloem vascular
cambium
xylem
stem
vascular bundle
Fig. 17-11
17.5 How Do Stems Grow And What Do
They Do?
 The epidermis of the stem retards water
loss while allowing carbon dioxide to enter.
• The epidermis is perforated with adjustable
pores called stomata (singular, stoma) that
permit and regulate the movement of carbon
dioxide and oxygen.
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
 The cortex and pith support the stem, store
food, and photosynthesize.
• There are two types of ground tissue in stems:
• Cortex
• Pith
• These ground tissues perform three major
functions—support, storage, and
photosynthesis.
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
 Vascular tissues in stems transport water,
dissolved nutrients, and hormones.
• Xylem and phloem of stems transport water,
nutrients, sugars, and hormones.
• Vascular tissues are continuous in the root,
stem, and leaf, interconnecting all parts of the
plant.
• Xylem and phloem in young stems arise from
the apical meristem, and are called primary
xylem and primary phloem.
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
 Branches form from lateral buds consisting
of meristem cells.
• As the shoot grows, small clusters of meristem
cells are left behind on the surface of the
stem.
• Some of these meristem cells form leaves,
and others form lateral buds that grow into
branches.
• Lateral buds are located just above the
attachment points of leaves.
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17.5 How Do Stems Grow And What Do
They Do?
 A bud sprouts from
these meristem cells
when stimulated by
a hormone, and this
becomes a branch
that has its own
apical meristem and
makes its own
leaves.
Fig. 17-12
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17.5 How Do Stems Grow And What Do
They Do?
 Secondary growth produces thicker,
stronger stems.
• Secondary growth results from cell division in
two lateral meristems:
• The vascular meristem
• The cork cambium
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17.5 How Do Stems Grow And What Do
They Do?
 Vascular cambium produces secondary
xylem and phloem.
• The vascular cambium is a cylinder of
meristem cells located between the primary
xylem and the primary phloem.
• Daughter cells of the vascular cambium
produced toward the inside of the stem
differentiate into secondary xylem, and those
produced toward the outside of the stem
differentiate into secondary phloem.
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
 Vascular cambium produces secondary
xylem and phloem (continued).
• Since the center of the stem already is filled
with pith and primary xylem, newly formed
secondary xylem pushes the vascular
cambium farther out, increasing the diameter
of the stem.
Copyright © 2009 Pearson Education Inc.
Secondary growth
(a) Cross section of stem
End of primary
growth
secondary phloem
primary phloem
vascular cambium
primary xylem
secondary xylem
epidermis
cork cambium
cork
pith
cortex
pith
cortex
primary
xylem
primary xylem
dividing
vascular
cambium
new
secondary
xylem
dividing
vascular
cambium
new
secondary
phloem
primary phloem
(b) Detail of vascular bundle
primary
phloem
Fig. 17-13
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17.5 How Do Stems Grow And What Do
They Do?
 Tree rings reflect seasonal changes.
• Tree rings form from seasonal changes in
vascular cambium growth.
• In temperate climates, vascular cambium
growth ceases in the winter but starts to grow
in the spring, forming new xylem and phloem.
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
 Tree rings reflect seasonal changes
(continued).
• In spring months, the new cells are large due
to extensive water uptake, but in summer
months, when water is more scarce, the cells
are smaller.
• As a result, cross-sections of tree trunks show
a banding pattern of these different cells that
form annual growth rings, which can be used
to age the tree.
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
 Secondary growth causes the epidermis to
be replaced by woody cork.
• Epidermal cells are mature, differentiated cells
that can no longer divide.
• Therefore, as new secondary xylem and
phloem enlarge the stem, the epidermis splits
and dies.
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
 Secondary growth causes the epidermis to
be replaced by woody cork (continued).
• Then some cells of the cortex form a new
lateral meristem—the cork cambium—which
produces daughter cells toward the outside of
the stem.
• These daughter cells become cork cells that
protect the tree from damage as they become
part of the tree bark.
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
PLAY
Animation—Primary and Secondary Growth
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
 Some specialized stems produce new
plants or store water or food.
• Many plants have stems that are modified to
perform functions very different from the
original one of raising leaves up to the light.
Copyright © 2009 Pearson Education Inc.
17.5 How Do Stems Grow And What Do
They Do?
 Strawberries grow stems that snake out
over the soil, sprouting new strawberry
plants where lateral buds touch the soil.
Fig. 17-14a
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17.5 How Do Stems Grow And What Do
They Do?
 The Baobab tree
stores water in
aboveground stems;
other plants, such as
the potato, store
carbohydrates in
underground stems.
Fig. 17-14b
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17.6 What Is The Structure Of Leaves And
What Do They Do?
 Leaves are the major site of photosynthesis
in plants.
 Photosynthesis produces sugars (glucose)
and oxygen from water, CO2, and sunlight.
Copyright © 2009 Pearson Education Inc.
17.6 What Is The Structure Of Leaves And
What Do They Do?
 Leaves have two major parts:
• The leaf epidermis consists of a layer of
nonphotosynthetic, transparent cells that
secrete a cuticle that reduces evaporation;
adjustable pores called stomata surrounded
by guard cells occur throughout the epidermis
and regulate gas exchange.
• Beneath the epidermis is the mesophyll, which
contains the chloroplasts for photosynthesis.
Copyright © 2009 Pearson Education Inc.
17.6 What Is The Structure Of Leaves And
What Do They Do?
 A typical dicot leaf
cuticle
upper
epidermis
chloroplasts
upper
epidermis
mesophyll
lower
epidermis
cuticle xylem phloem
(a) Leaf structure
guard cell stoma
stoma phloem
lower
epidermis
(b) Leaf cross section
xylem
Fig. 17-15
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17.6 What Is The Structure Of Leaves And
What Do They Do?
 Specialized leaves may provide support,
store food, or even capture insects.
• In some plants, modified leaves serve
functions unrelated to photosynthesis or water
conservation.
• The common edible pea grasps fences with
clinging tendrils, which are slender, supple
leaflets.
• Some plants—like onions, daffodils, and
tulips—use thick, fleshy leaves as foodstorage organs.
Copyright © 2009 Pearson Education Inc.
17.6 What Is The Structure Of Leaves And
What Do They Do?
 A few plants have become predators;
sundews have leaves that are modified into
snares for trapping insects.
Fig. 17-16
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17.7 How Do Plants Acquire Nutrients?
 Plants require a long list of important
nutrients for normal life, which come from
the soil or air.
•
•
•
•
•
Carbon dioxide
Hydrogen and oxygen
Phosphorus
Nitrogen
Minerals such as magnesium, calcium, and
potassium
• Micronutrients such as iron, copper,
manganese, zinc, boron, and molybdenum
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17.7 How Do Plants Acquire Nutrients?
 Fungi and bacteria
help plants acquire
nutrients.
• Root-fungus
complexes are
called mycorrhizae,
and they help plants
extract and absorb
minerals from the
soil.
Fig. 17-17
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17.7 How Do Plants Acquire Nutrients?
 Plants need a lot of nitrogen; much comes
from the air, but some plants have symbiotic
bacteria in root nodules that convert N2 gas
into ammonium or nitrate, which the plants
can then use.
 This process is called nitrogen-fixation.
• Plants that have nitrogen-fixing bacteria are
called legumes (e.g., peas, clover, and
soybeans).
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17.7 How Do Plants Acquire Nutrients?
 Nitrogen fixation in legumes
Fig. 17-18
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17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?
 Nearly 99% of the water absorbed by the
roots of plants evaporates through the
stomata of leaves in a process called
transpiration.
• Transpiration drives the movement of water
through the plant body by pulling water up
through the xylem of the roots and stem into
the leaves.
Copyright © 2009 Pearson Education Inc.
17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?
 Transpiration provides the force for water
movement in xylem.
• As the leaf transpires, the water concentration
in its mesophyll drops, which causes water to
move by osmosis from the leaf’s xylem into
the mesophyll cells.
• Because of hydrogen bonding between
adjacent water molecules, when one water
molecule leaves, it pulls other water molecules
up the xylem from the stem and the roots.
Copyright © 2009 Pearson Education Inc.
Water evaporates
through the stomata
of leaves
flow of water
water molecules
Cohesion of water
molecules to one
another and adhesion
to the xylem wall by
hydrogen bonds
creates a “water chain”
Water enters
the vascular
cylinder of the root
Fig. 17-19
Copyright © 2009 Pearson Education Inc.
17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?
 Water enters roots mainly by pressure
differences created by transpiration.
• The upward movement of water ultimately
causes soil water to move into the roots.
• The main force powering the flow of water
from the soil to the root’s vascular cylinder is
low water pressure in the cylinder.
Copyright © 2009 Pearson Education Inc.
17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?
 Water enters roots mainly by pressure
differences created by transpiration
(continued).
• This low pressure is due to the fact that water
is always drawn away by moving upward
through the xylem to replace water lost
through transpiration from the leaves.
• This force is strong enough that roots can
absorb water, even from quite dry soils.
Copyright © 2009 Pearson Education Inc.
17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?
 Adjustable stomata control the rate of
transpiration.
• Transpiration is a plant’s largest source of
water loss.
• Most water is lost through the stomata in the
leaves; because photosynthesis requires
carbon dioxide from the air, the stomata have
to be open to obtain this gas.
• To meet these requirements, stomata are
open during the day, when sunlight allows
photosynthesis, and closed at night,
conserving water.
Copyright © 2009 Pearson Education Inc.
17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?
PLAY
Animation—Plant Transport Mechanisms
Copyright © 2009 Pearson Education Inc.
Water Transport In Plants
Suggested Media Enhancement:
Water Transport in Plants
To access this animation go to folder C_Animations_and_Video_Files
and open the BioFlix folder.
Copyright © 2009 Pearson Education Inc.
17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?
 The pressure-flow theory explains sugar
movement in phloem.
• Sugars made by photosynthesis must be
moved to other parts of the plant.
• Sugars, dissolved in water to form sap, also
contain amino acids and hormones, and travel
throughout the phloem.
Copyright © 2009 Pearson Education Inc.
17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?
 The pressure-flow theory explains sugar
movement in phloem (continued).
• After reaching their destination, the sugars
may nourish non-photosynthetic cells of roots
or flowers, or may be stored for later use.
• Sap is propelled through phloem by
differences in water pressure created by the
difference between the production and use of
sugar in different parts of the plant.
Copyright © 2009 Pearson Education Inc.
17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?

The pressure flow theory is illustrated in four
steps.
1. The sugar produced by a source cell is moved by
active transport into a phloem tube.
2. Water follows the sugar into the tube by osmosis.
3. The increased water pressure forces the sugar-rich
sap through the phloem tubes into regions of lower
pressure.
4. Cells of a sugar sink actively transport sugar out of
the phloem, with water following by osmosis.
Copyright © 2009 Pearson Education Inc.
17.8 How Do Plants Acquire Water And
Transport Water And Nutrients?
 Pressure differences power the movement
of sugars.
xylem
phloem
sunlight
sugar
source
sugar
source
cell
sugar
sink
sugar
sink cell
Fig. 17-20
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