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Plant Form
Chapter 36
Plant Body Organization
A vascular plant consists of:
1. Root system, which is underground
-Anchors the plant, and is used to
absorb water and minerals
2. Shoot system, which is above ground
-Consists of supporting stems,
photosynthetic leaves and reproductive
flowers
Each has an apex that extends growth
2
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Shoot apex
Flower
Stipule
Axillary
bud
Internode
Node
Tendril
Vein
Leaflet
Shoot
Leaf
Blade
Petiole
Vascular system
Primary root
Lateral root
Root
Root apex
3
Plant Body Organization
Plant cell walls consist of cellulose
-Primary cell wall
-Found in all cells
-Cellulose fibers parallel to microtubules
-Secondary cell wall
-Found in some cells
-Additional layers of cellulose and lignin
-Increase mechanical strength of wall
4
Plant Body Organization
Cellulose fiber
Cell membrane
Cell membrane
Cytosol
Microtubule
Cytosol
Time
Celluloseforming
rosettes
a.
Parallel
cellulose
fibers
b.
Primary cell wall
Primary cell wall
remains outside
as inner layers
are laid down
Secondary
cell wall 1
Secondary
cell wall 2
5
Plant Body Organization
Roots, shoots and leaves contain three basic
tissue systems:
-Dermal tissue – For protection
-Wax and bark
-Ground tissue – For storage,
photosynthesis and secretion
-Vascular tissue – For conduction
-Xylem – Water and dissolved minerals
-Phloem – Nutrient-containing solution
6
Plant Body Organization
Meristems are clumps of small cells with
dense cytoplasm and large nuclei
They act as stem cells do in animals
-One cell divides producing a differentiating
cell and another that remains meristematic
7
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Meristem cell
Cell division
Meristem cell
Differentiated cell
Cell division
Meristem cell
Differentiated cell
Cell division
Meristem cell
Differentiated cell
8
Plant Body Organization
Apical meristems are located at the tips of
stems and roots
-Give rise to primary tissues which are
collectively called the primary plant body
-Three primary meristems
-Protoderm  Epidermis
-Procambium  1o vascular tissue
-Ground meristem  Ground tissue
9
Plant Body Organization
10
Plant Body Organization
Lateral meristems are found in plants that
exhibit secondary growth
-Give rise to secondary tissues which are
collectively called the secondary plant body
-Woody plants have two types
-Cork cambium  Outer bark
-Vascular cambium  2o vascular tissue
11
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Primary Root
Secondary Root
Secondary Stem
Primary Stem
Ground meristem
Procambium
Primary
xylem
Apical
growth
Primary
phloem
Vascular
cambium
Lateral
growth
Cork cambium
Secondary
xylem
Secondary
phloem
Vascular
cambium
Primary
phloem
Primary
xylem
Primary
xylem
Secondary
xylem
Primary
phloem
Lateral
growth
Secondary
phloem
Primary
xylem
Apical
growth
Ground meristem
Primary
phloem
Procambium
12
Plant Tissues
As mentioned earlier, plants contain three
main types of tissue
-Dermal
-Ground
-Vascular
13
Dermal Tissue
Forms the epidermis, which is usually one
cell layer thick
Covered with a fatty cutin layer constituting
the cuticle
Contains special cells, including guard cells,
trichomes and root hairs
14
Dermal Tissue
Guard cells are paired sausage-shaped cells
-Flank a stoma, which is the passageway
for oxygen and carbon dioxide
Guard cell formation is the result of an
asymmetrical cell division that produces:
-A guard cell
-A subsidiary cell
-Aids in stoma opening and closing
15
Dermal Tissue
16
Dermal Tissue
Trichomes are cellular or multicellular hairlike
outgrowths of the epidermis
-Keep leaf surfaces cool and reduce
evaporation by covering stomatal openings
-Some are glandular,
secreting substances
that deter herbivory
Trichome patterning is
under genetic control
17
Dermal Tissue
18
Dermal Tissue
Roots hairs are tubular extensions of
individual epidermal cells
-Greatly increase
the root’s surface
area and efficiency
of absorption
19
Ground Tissue
Consist of three types of cells
-Parenchyma
-Collenchyma
-Sclerenchyma
20
Ground Tissue
Parenchyma cells are the most common
type of plant cell
-May live for many years, functioning in
storage, photosynthesis and secretion
-Some contain chloroplasts and are called
chlorenchyma
Collenchyma cells provide support for plant
organs, allowing bending but not breaking
-Have living protoplasts and may live for
many years
21
Ground Tissue
Sclerenchyma cells have tough thick walls
-Lack living walls at maturity
-Two general types
-Fibers: Long, slender cells that are
usually grouped in strands
-Sclereids: Variable shape; branched;
may occur singly or in groups
-Both strengthen tissues
22
Ground Tissue
23
Vascular Tissue
Xylem
-Constitutes the main water- and mineralconducting tissue
-Vessels: Continuous tubes of dead
cylindrical cells arranged end-to-end
-Tracheids: Dead cells that taper at the
end and overlap one another
-Vessels are shorter & wider than tracheids
-And conduct water more efficiently 24
25
Vascular Tissue
Xylem
-Also conducts inorganic ions such as
nitrates, and supports the plant body
-Typically includes parenchyma cells in
horizontal rows called rays
-Function in lateral conduction and food
storage
Note: The diffusion of water vapor from a
plant is termed transpiration
26
Vascular Tissue
Phloem
-Constitutes the main food-conducting
tissue in vascular plants
-Contains two types of elongated cells:
sieve cells and sieve tube members
-Living cells that contain clusters of
pores called sieve areas or sieve plates
-Sieve-tube members are more
specialized
-Associated with companion cells 27
28
Roots
Roots have a simpler pattern of organization
and development than stems
Four regions are commonly recognized:
-Root cap
-Zone of cell division
-Zone of elongation
-Zone of maturation
29
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
dermal tissue
ground tissue
vascular tissue
Root in
cross-section
Endodermis
Root hair
Epidermis
Ground
tissue
Vascular
tissue
Ground
meristem
Procambium
Protoderm
Quiescent
center
Apical meristem
Columella cells
Zone of
maturation
Zone of
elongation
Zone of
cell division
Root cap
30
Roots
Root cap
-Contains two types of cells that are formed
continuously by the root apical meristem
-Columella cells: Inner
-Root cap cells: Outer and lateral
-Functions mainly in protection of the
delicate tissues behind it
-Also in the perception of gravity
31
Roots
Zone of cell division
-Contains mostly cuboidal cells, with small
vacuoles and large central nuclei
-Derived from rapid divisions of the root
apical meristem
-Quiescent center cells divide very
infrequently
-Apical meristem daughter cells soon
subdivide into the three primary tissues 32
Roots
Zone of cell division
-Patterning of these tissues begins in this
zone
-WEREWOLF (WER) gene
-Suppresses root hair development
-SCARECROW (SCR) gene
-Necessary for differentiation of
endodermal and ground cells
33
wer (mutant)
WER (wild type)
Nonhair
WER
No
WER
Hair will develop in
zone of maturation
No
WER
No
WER
Hair will develop in
zone of maturation
Root tip
Epidermal cell
a.
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scr (mutant)
SCR (wild type)
2 layers of cells
Root tip
Root tip
Endodermal Ground
cell
cell
SCR
Ground
meristem
cell
Asymmetrical
division
Cell with
ground and
endodermal
SCR traits
Ground
meristem
cell
a.
35
Roots
Zone of elongation
-Roots lengthen because cells become
several times longer than wide
-No further increase occurs above this zone
36
Roots
Zone of maturation
-The elongated cells become differentiated
into specific cell types
-Epidermal cells: Have very thin cuticle
-Include root hair and nonhair cells
-Cortex: Interior to the epidermis
-Parenchyma cells used for storage
37
Roots
Zone of maturation
-Endodermis: Single-layered cylinder
-Impregnated with bands of suberin
called the Casparian strips
-Stele: All tissues interior to endodermis
-Pericycle: Multiple-layered cylinder
-Gives rise to lateral (branch) roots
or the two lateral meristems
38
Roots
Phloem
Casparian strip
Xylem
Cortex
H2O
Pericycle
H2O
Endodermal cell
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40
Plant Tissue Differentiation
Cork cambium
Vascular cambium
Shoot apical meristem
Zygote
Phloem
Xylem
Leaf primordia
Leaves
Bud primordia
Lateral shoots
Bark
Shoot elongation
Embryo
Cork cambium
Root apical meristem
Outer bark
Inner bark
Wood
Vascular cambium
Pericycle
Phloem
Outer bark
Inner bark
Xylem
Wood
Lateral roots
Root elongation
41
Bark
Modified Roots
Most plants produce either/or:
-Taproot system: Single large root with
small branch roots
-Fibrous root system: Many small roots of
similar diameter
Some plants, however, produce modified
roots with specific functions
-Adventitious roots arise from any place
other than the plant’s root
42
Modified Roots
Prop roots: Keep the plant upright
Aerial roots: Obtain water from the air
Pneumatophores: Facilitate oxygen uptake
Contractile roots: Pull plant deeper into soil
Parasitic roots: Penetrate host plants
Food storage roots: Store carbohydrates
Water storage roots: Weigh 50 or more kg
Buttress roots: Provide considerable stability
43
Prop roots
Pneumatophores
Aerial roots
Water storage roots
Buttress roots
44
Stems
Like roots, stems contain the three types of
plant tissue
-Also undergo growth from cell division in
apical and lateral stems
Shoot apical meristem initiates stem tissue
and intermittently produces primordia
-Develop into leaves, other shoots and
even flowers
45
Stems
46
Stems
Leaves may be arranged in one of three ways
47
Stems
The spiral (alternate) arrangement is the
most common
-Sequential leaves tend to be placed
137.5o apart
-This is termed phyllotaxy
-May optimize the exposure of
leaves to the sun
48
External Stem Structure
Node = Point of attachment of leaf to stem
Internode = Area of stem between two nodes
Blade = Flattened part of leaf
Petiole = Stalk of leaf
Axil = Angle between petiole/blade and stem
Axillary bud = Develops into branches with
leaves or may form flowers
Terminal bud = Extends the shoot system
during the growing season
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50
Internal Stem Structure
Monocot vascular bundles are usually
scattered throughout ground tissue system
Eudicot vascular tissue is arranged in a ring
with internal ground tissue (pith) and
external ground tissue (cortex)
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52
Internal Stem Structure
Vascular tissue arrangement is directly related
to the stem’s ability for secondary growth
-In eudicots, a vascular cambium develops
between the primary xylem and phloem
-Connects the ring of primary vascular
bundles
-In monocots, there is no vascular cambium
-Therefore, no secondary growth
53
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Primary xylem
Epidermis
Primary phloem
a.
Primary xylem
Secondary xylem
b.
Primary phloem
Secondary phloem
Vascular cambium
(lateral meristem)
Annual growth layers
Primary xylem
Primary phloem
Secondary xylem
Secondary phloem
c.
Vascular cambium
(lateral meristem)
54
Internal Stem Structure
Rings in the stump of a tree reveal annual
patterns of vascular cambium growth
-Cell size depends on growth conditions
In woody eudicots and gymnosperms, the
cork cambium arises in the outer cortex
-Produces boxlike cork cells on outside and
parenchyma-like phelloderm cells on inside
-Collectively called the periderm
55
Internal Stem Structure
56
Internal Stem Structure
57
Internal Stem Structure
Cork tissue cells get impregnated with
suberin shortly after they are formed
-They then die and constitute the outer
bark
The cork cambium also produces
unsuberized cells called lenticels
-Permit gas exchange to continue
58
Internal Stem Structure
59
Modified Stems
Bulbs = Swollen underground stems,
consisting of fleshy leaves
Corms = Superficially resemble bulbs, but
have no fleshy leaves
Rhizomes = Horizontal underground stems,
with adventitious roots
Runners and stolons = Horizontal stems
with long internodes that grow along the
surface of the ground
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Modified Stems
Tubers = Swollen tips of rhizomes that
contain carbohydrates
Tendrils = Twine around supports and aid in
climbing
Cladophylls = Flattened photosynthetic
stems resembling leaves
61
Modified Stems
62
Leaves
Leaves are the main site of photosynthesis
-They are determinate structures whose
growth stops at maturity
Exist in two morphologies
-Microphyll = Have one vein which does
not extend the full length of the leaf
-Found mainly in the phylum Lycophyta
-Megaphylls = Have several to many veins
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Leaves
The flattening of the leaf blade reflects a shift
from radial to dorsal-ventral symmetry
-It increases the photosynthetic surface
The mechanism of this shift is becoming
clearer through the analysis of mutants that
lack distinct tops and bottoms
64
PHAVOLUTA
YABBY
PHABULOSA
KANADI
65
Leaves
Veins consist of both xylem and phloem and
are distributed throughout the leaf blades
-Monocot leaves
have parallel
veins
-Eudicot leaves have
netted or reticulate
veins
66
Leaves
Leaf blades come in a variety of forms
-Simple leaves contain undivided blades
-May have teeth, indentations or lobes
-Compound leaves have blades that are
divided into leaflets
-Pinnate = Leaflets in pairs along an axis
-Palmate = Leaflets radiate out from a
common point
67
Leaves
68
Leaves
The leaf’s surface is covered by transparent
epidermal cells, most having no chloroplasts
Epidermis has a waxy cuticle
-The lower epidermis contains numerous
mouth-shaped stomata flanked by guard
cells
69
Leaves
70
Leaves
The mesophyll is the tissue between the
upper and lower epidermis
-Most eudicot leaves have two types
-Palisade mesophyll = Usually two rows
of tightly packed chlorenchyma cells
-Spongy mesophyll = Loosely arranged
cells with many air spaces in between
-Monocot leaves mesophyll is usually not
differentiated into palisade/spongy layers 71
Leaves
72
Modified Leaves
Floral leaves (bracts) = Surround true
flowers and behave as showy petals
Spines = Reduce water loss and may deter
predators
Reproductive leaves = Plantlets capable of
growing independently into full-sized plant
Window leaves = Succulent, cone-shaped
leaves that allow photosynthesis
underground
73
Modified Leaves
Shade leaves = Larger in surface area but
with less mesophyll than sun-lit leaves
Insectivorous leaves = Trap insects
-Pitcher plants have cone-shaped leaves
that accumulate rainwater
-Sundews have glands that secrete sticky
mucilage
-Venus flytrap have hinged leaves that
snap shut
74