Download Fig. 26.5 - McGraw Hill Higher Education

Essentials of
The Living World
First Edition
GEORGE B. JOHNSON
26
Plant Form
And Function
PowerPoint® Lectures prepared by Johnny El-Rady
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26.1 Organization of a Vascular Plant
Vascular plants have an outer covering of protective
tissue & an inner matrix of vascular conductive tissue
A vascular plant is organized along a vertical axis
Root: The part belowground
Shoot: The part aboveground
Stem
Leaves
Sites of photosynthesis
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Plants contain meristems, which are growth zones of
unspecialized cells whose main function is to divide
Apical meristems
Responsible for primary growth
Results in elongation of the plant body
Lateral meristems
Responsible for secondary growth
Results in increase in thickness of the plant body
Vascular cambium
Gives rise to secondary xylem and phloem
Cork cambium
Gives rise to outer layer of bark
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Fig. 26.1 The
body of a plant
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26.2 Plant Tissue Types
Most plants have three major tissue types
1. Ground tissue
Contains the vascular tissue
2. Dermal tissue
Outer protective layer
3. Vascular tissue
Conducts water, dissolved minerals and
carbohydrates
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Ground Tissue
Makes up the main body of the plant
Contains several different cell types
Parenchyma cells
Least specialized and
most common
Alive at maturity
Carry out photosynthesis
and storage functions
Have thin primary cell
walls
Fig. 26.2
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Collenchyma cells
Alive at maturity
Uneven primary cell walls
Form strands & cylinders
that provide support
Sclerenchyma cells
Fig. 26.3
Dead at maturity
Thick secondary cell walls
Provide strength and
rigidity
Fibers are long and slender
Sclereids are variable and
branched
Fig. 26.4
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Dermal Tissue
The epidermis of a plant is often covered with a
thick waxy layer called the cuticle
Guard cells
Paired cells with
openings between
them (stomata)
Allow gas exchange
Fig. 26.5
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Trichomes
Outgrowths of the
epidermis, occurring on
shoots
Variable in form
Regulate heat and
water balance
Fig. 26.5
Root hairs
Fig. 26.22
Outgrowths of the
epidermis, occurring on
roots
Increase the surface
area for absorption
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Vascular Tissue
Consists of xylem and phloem
Xylem
Principal water-conducting tissue
Composed of tracheids and vessel elements
Both have thick secondary cell walls and are dead at
maturity
Tracheids are connected by pits in their cell walls
Vessel elements are connected by perforations
A linked row of vessel elements forms a vessel
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Fig. 26.6 Comparison of vessel elements and tracheids
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Vascular Tissue
Phloem
Principal food-conducting tissue
Composed of sieve cells and sieve-tube members
Both are living, but lack nuclei at maturity
A linked row of sieve-tube members forms a sieve tube
Companion cells
Specialized cells found adjacent to sieve-tube
members
Carry out metabolic functions needed to maintain
sieve-tube members
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Fig. 26.7 Sieve tubes
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26.3 Roots
Roots have a central column of xylem with radiating
arms, alternating with strands of primary phloem
The pericycle is a layer of cells surrounding the
vascular tissue
The endodermis lies outside the pericycle
It is encircled by a thickened waxy band, the
Casparian strip
It controls the movement of water into the
endodermis
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There are three primary meristems
Protoderm: produces the epidermis
Procambium: produces the vascular tissue
Ground meristem: produces the ground tissue
The root cap covers & protects the apical meristem
Zone of elongation
Newly-formed cells are elongating, causing the root to
reach further into the soil
Zone of differentiation
Cells are taking on specialized forms and functions
Example: Root hairs
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Fig. 26.8 Root structure
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A fundamental difference between roots and
shoots has to do with branching
In stems, branching
originates at the
surface
In roots, branching
originates below the
surface
Fig. 26.10 Lateral roots
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26.4 Stems
Stems serve two purposes
Main structural support for plant
Famework for positioning the leaves
Stems often experience two types of growth
Primary growth
Secondary growth
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Primary Growth
Leaves cluster around apical meristem, unfolding
and growing as the stem elongates
Leaves grow out of
stems at the nodes
Buds develop in the
axil of each leaf
A terminal bud
hormone continuously
suppresses
expansion of lateral
buds
Fig. 26.11 A woody twig
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The arrangement of vascular tissue in stems differs
In dicots, the vascular bundles are arranged around the
outside of the stem
In monocots, the vascular bundles are scattered
throughout the stem
Fig. 26.12
Pith = Inner portion
of ground tissue
Cortex = Outer portion
of ground tissue
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Secondary Growth
Results from the differentiation of lateral meristems
Vascular cambium and cork cambium
The vascular cambium develops from a thin cell
layer located between the primary xylem and phloem
It divides outwardly to produce the secondary phloem
Inward division results in the secondary xylem
The cork cambium develops in the stem’s outer layer
Outwardly, it splits off densely packed cork cells
Inwardly, it divides to produce a layer of parenchyma cells
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Fig. 26.13 Vascular cambium and secondary growth
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Bark refers to all of the tissues outside the vascular
cambium
Wood, anatomically-speaking, is accumulated
secondary xylem
Because of the way
it is accumulated,
wood often
displays rings
In temperate
regions, these
rings are annual
rings
Fig. 26.14 Annual rings in pine
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26.5 Leaves
Leaves are outgrowths of the shoot apex
They are the major light-capturing organs of most
plants
Leaves grow outward by marginal meristems
This ultimately forms the blade (flattened portion)
Most leaves also have
A petiole – slender stalk
Stipules – leaflike organs flanking the petiole
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Veins (xylem and phloem) run through leaves
Most dicots have leaves with netted or reticulate
veins
Most monocots have leaves with parallel veins
Fig. 26.16
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Leaf blades come in
different forms
Simple leaves
have a single
undivided blade
Fig. 26.15a
Compound leaves have blades divided into leaflets
Pinnately compound leaves
Leaflets arranged in pairs
along a common axis
Fig. 26.15c
Palmately compound leaves
Leaflets radiate out from
a common point
Fig. 26.15d
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There are three common types of leaf arrangements
Alternate
Opposite
Two leaves
per node
Whorled
Circle of leaves
at the same
node level
One leaf
per node
Fig. 26.17
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A leaf consists of parenchyma tissue called mesophyll
Two types: palisade and spongy
Fig. 26.18 A leaf in cross section
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Allow passage
of CO2
26.6 Water Movement
Plants use chains of specialized cells to carry out
transport function
Phloem transports photosynthetically-produced
carbohydrates up and down the plant
Xylem transports water and minerals upward
But how can water be moved up to the height of a
plant?
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Cohesion-Adhesion-Tension Theory
The initial movement of water into the roots of a plant
involves osmosis
This root pressure
provides a “push”
Capillary action adds
a “pull”
This is a result of
adhesion
Fig. 26.19
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The narrower the
tube, the higher
the water rises
Transpiration provides a second very strong “pull”
Passage of air across leaf surfaces results in loss
of water by evaporation
This creates a “pull” at the open upper end of the
plant
Water molecules entering the roots are pulled up
Water molecules undergo cohesion because of their
tendency to form hydrogen bonds with one another
Thus, a column of water resists separation
This resistance is called tensile strength
It varies inversely with the column diameter
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Transpiration
The process by which water leaves the plant
> 90% of water taken in by roots is lost to the atmosphere
Fig. 26.20
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Transpiration
Factors affecting evaporation also affect transpiration
Humidity levels
High humidity reduces evaporation
Low humidity increases it
Temperature
High temperature increases evaporation
Low humidity decreases it
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Regulation of Transpiration
Plants control short-term water loss by closing
stomata
But the stomata must be opened to obtain CO2
The stomata open and close because of changes in
water pressure of their guard cells
Water entering guard cells causes them to bow outward
This opens the stomata
Water leaving guard cells causes them to wilt
This closes the stomata
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Guard cells
turgid
Guard cells
flaccid
Fig. 26.21
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Water Absorption by Roots
Most of the water absorbed
by plants comes in through
root hairs
Root hairs are greatly
reduced in number in plants
with ectomycorrhizae
Fig. 26.22
Fungal filaments take their place in promoting absorption
Minerals also enter the root through root hairs
These are transported to the rest of the plant via the xylem
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Fig. 26.23 The transport of materials into, out of, and within a plant
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26.7 Carbohydrate Transport
Carbohydrates manufactured in plant leaves is
moved through the phloem to other parts of the plant
This process is known as translocation
It does not require energy
The mass flow of materials occurs because of
water pressure
Water pressure develops as a result of
osmosis
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Fig. 26.24 How translocation works
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26.8 Essential Nutrients
Plants require many nutrients
Nitrogen (N)
Part of proteins and nucleic acids
Potassium (K)
Regulates turgor pressure
Calcium (Ca)
Part of middle lamellae
Magnesium (Mg)
Part of the chlorophyll molecule
Phosphorus (P)
Part of nucleic acids and ATP
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Most plants acquire nutrients from the soil
However, carnivorous plants use other organisms
directly as nutrient sources
Venus’sflytrap
Fig. 26.25
Asian pitcher plant
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