Chapter 31
Plant Structure, Growth, and
Reproduction
Dr. Sharaf Al-Tardeh
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In northern California, coast redwoods (Sequoia sempervirens)
are the tallest trees in the world. The tallest one, named
Hyperion: 115.5 m. Estimated to be over 2,000 years old
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31.2 The two major groups of angiosperms
are the monocots and the eudicots
 Most of our foods come from a few hundred
domesticated species of flowering plants
 Angiosperms placed into two groups: monocots
and dicots.
 The names monocot and dicot refer to: the first
leaves on the plant embryo. These embryonic
leaves are called seed leaves, or cotyledons
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Eudicots
 The great majority of dicots, called the eudicots
(“true” dicots):
are evolutionarily related, having diverged
from a common ancestor about 125 million
years ago
a few smaller groups of dicots have evolved
independently
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Monocots
 A monocot embryo has one seed leaf
 Monocots: are a large group of related plants that
include the orchids, bamboos, palms, and lilies,
as well as the grains and other grasses.
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Eudicots
 a dicot embryo has two seed leaves
 Most flowering shrubs and trees are eudicots,
such as the majority of our ornamental plants
and many of our food crops, including nearly
all of our fruits and vegetables
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31.3 A typical plant body contains three
basic organs: roots, stems, and leaves
 Plants
Have organs composed of different (several types )
tissues (a group of cells)
The Three Basic Plant Organs: Roots, Stems, and Leaves
– terrestrial organisms draw nutrients from two very
different environments:
1. below-ground (water and minerals)
2. above-ground (CO2 and light).
To solve this separation in resources, 3 basic organs were
developed: Roots, stems and leaves.
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 The basic evolved
organs: roots, stems, and
leaves were organized
into:
1. a root system
2. a shoot system
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Roots
 A root functions:
1. Anchors the vascular plant
2. Absorbs minerals and water
3. Stores organic nutrients to be used for
flowering and fruit production thus, root plants
(e.g potato, carrot) are harvested before flowering:
such as in angiosperms (flowering plants, their
seeds is covered)
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Root systems
1. Taproot system: that give rise to lateral roots
such as in Most eudicots and gymnosperms (no
cover for the seeds).
2. Fibrous root system: a mat of generally thin
roots with no stem holding them.
3. Adventitious Roots: those are arising from the
stem.
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• In most plants
– The absorption of water and minerals occurs near
the root tips, where vast numbers of tiny root hairs
increase the surface area of the root
– Note; root hairs are not lateral roots
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 Many plants have modified roots
This occurs in Maize
where these roots will
penetrate soil
(b) Storage roots
Red (sweet)
(a) Prop roots
potato
(d) Buttress roots
(c) “Strangling” aerial
roots
(e) Pneumatophores (air roots)
These air roots gets oxygen
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Stems
 A stem is an organ consisting of an alternating
system of:
1. Nodes: the points at which leaves are
attached
2. Internodes: the stem segments between
nodes
 An axillary bud (most of them are dormant):
– Is a structure that has the potential to
form a lateral shoot, or branch
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 A terminal bud:
– Is located near the shoot tip and causes
elongation of a young shoot
– The proximity (closeness) of the terminal
bud is responsible for inhibiting the
growth of the axillary bud. This
phenomenon is called apical dominance
which increases the plant exposure to
light.
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Many plants have modified stems
(a) Stolons. Shown here on a strawberry plant, stolons are horizontal stems
that grow along the surface. These “runners” enable a plant to reproduce
asexually, as plantlets form at nodes along each runner.
Storage leaves
Stem
Root
Node
(b) Bulbs. Bulbs are vertical,
underground shoots consisting
mostly of the enlarged bases
of leaves that store food. You
can see the many layers of
modified leaves attached
to the short stem by slicing an
onion bulb lengthwise.
(c) Tubers. Tubers, such as these
potatoes, are enlarged
ends of rhizomes specialized
for storing food. The “eyes”
arranged in a spiral pattern
around a potato are clusters
of axillary buds that mark
the nodes.
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Rhizome
Root
(d) Rhizomes. The edible base of this ginger
plant is an example of a rhizome, a
horizontal stem that grows just below the
surface or emerges and grows along the
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surface.
Leaves
 The leaf: Is the main photosynthetic organ of
most vascular plants. Green stems also perform
photosynthesis.
 Leaves generally consist of:
– A flattened blade and a stalk
– The petiole: which joins the leaf to a node of
the stem
– Among the angiosperms, grasses and many
other monocots lack petioles. However,
palm trees which are monocots have
petioles.
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 Monocots and eudicots: Differ in the
arrangement of veins and the vascular tissue of
leaves.
 Most monocots: Have parallel veins
 Most eudicots: Have multibranching veins
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In classifying angiosperms
 Taxonomists may use leaf morphology as a criterion for
classification.
(a) Simple leaf. A simple leaf
is a single, undivided blade.
Some simple leaves are
deeply lobed, as in an
oak leaf.
(b) Compound leaf. In a
compound leaf, the
blade consists of
multiple leaflets.
Notice that a leaflet
has no axillary bud
at its base.
(c) Doubly compound leaf.
In a doubly compound
leaf, each leaflet is
divided into smaller
leaflets.
Figure 35.6a–c
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Petiole
Axillary bud
Leaflet
Petiole
Axillary bud
Leaflet
Petiole
Axillary bud
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Some plant species
 Have evolved modified leaves that serve various functions
(a)Tendrils. The tendrils by which this
pea plant clings to a support are
modified leaves. After it has “lassoed”
a support, a tendril forms a coil that
brings the plant closer to the support.
Tendrils are typically modified leaves,
but some tendrils are modified stems,
as in grapevines.
(b)Spines. The spines of cacti, such
as this prickly pear, are actually
leaves, and photosynthesis is
carried out mainly by the fleshy
green stems.
(c) Storage leaves. Most succulents,
such as this ice plant, have leaves
modified for storing water.
(e) Reproductive leaves. The leaves
of some succulents, such as Kalanchoe
daigremontiana, produce adventitious
plantlets, which fall off the leaf and
take root in the soil.
(d)Bracts. Red parts of the poinsettia
are often mistaken for petals but are
actually modified leaves called bracts
that surround a group of flowers.
Such brightly colored leaves attract
pollinators.
Figure 35.6a–e
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31.5 Three tissue systems make up the plant
body
• Each plant organ
– Has (1) dermal, (2) vascular, and (3) ground
tissues
Figure 35.8
Dermal
tissue
Ground
tissue
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Vascular
tissue
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1. The dermal tissue system:
– Is the outer protecting cover.
– Consists of the epidermis (none woody plants)
and periderm (in woody plants).
– Like human skin, it forms the first line of
defense against physical damage and pathogens.
– In the epidermis of leaves presents a waxy
material called cuticle prevents loss of water.
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 The dermal tissue also referred
to as the epidermis: is the skin
of the plant and functions to
protect
the
plant
from
potentially harmful effects
 The protective nature comes
from a thin cuticle surrounding
the epidermal cells.
 The cuticle: is a non-cellular
protective layer containing wax
and other components giving the
plant its protective coating.
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2. The vascular tissue system (Stele):
– Carries out long-distance transport of materials between
roots and shoots
– It divided into two types:
1. Xylem {xylem up}
– The xylem is found in the innermost ring of the vascular
tissue
– Conveys (transports) water and dissolved minerals
upward from roots into the shoots
2. Phloem {phloem down}
– the phloem surrounds the xylem
– Transports organic nutrients from where they are made
(source) to where they are needed (sink) such as
developing leaves and fruits
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Vascular bundle
 vascular bundle: is a part of the transport system
in vascular plants.
 Vascular bundle consists of xylem and phloem, as
well as supporting and protective tissues.
 It is a vein in the leaf.
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Xylem is composed of:
1. Tracheids: thin, long and tapered at ends.
 the chief water-conducting cells in gymnosperms
i.e., seedless vascular plants i.e., pines.
WATER-CONDUCTING CELLS OF THE XYLEM
2. Vessel elements: short, wide, Vessel
Tracheids
perforated end, pitted walls
located in angiosperms.
 the xylem is a complex tissue
which means that it includes
Tracheids and vessels
Vessel
more than one type of cell such
element
as parenchyma
Vessel elements with partially
perforated end walls
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100 m
Pits
Tracheids
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Phloem
 Phloem: is the living tissue
 Phloem tissue consists of sieve-tube cells, and
companion cells
SUGAR-CONDUCTING CELLS OF THE PHLOEM
Sieve-tube members:
longitudinal view
 The end walls of these cells have
many small pores and are called
sieve plates
Companion cell
Sieve-tube
member
Sieve
plate
Nucleus
30 m
15 m
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Cytoplasm
Companion
cell
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3. Ground tissue:
– Tissues that are neither dermal nor vascular
– Includes various cells specialized for functions
such as storage, photosynthesis, and support
– Ground tissue internal to the vascular tissue
is called the pith while the one external to the
ground tissue is called the cortex.
– Consist of three simple tissue: parenchyma,
collenchyma and sclernchyma.
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31.6 Plant cells are diverse in structure
and function
 Some of the major types of plant cells include:
1. Parenchyma: least specialized cells, function
in photosynthesis and storing nutrients
2. Collenchyma: are living cells elongates with
growing stems and leaves.
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3. Sclerenchyma: function in support,
and divided to; Fibers and Sclerids.
– Water-conducting cells of the xylem
– Sugar-conducting cells of the phloem
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Parenchyma
 Parenchyma cells are living cells that form parenchyma
tissue.
1. Parenchyma cells are the most abundant type and are
found in almost all major parts of higher plants.
2. These cells are basically sphere shaped when they are
first made. However, these cells have thin walls, which
flatten at the points of contact when many cells are
packed together.
3. These cells have large vacuoles and may contain
various secretions including starch, oils, tannins, and
crystals.
4. Have a space between cells called intercellular space.
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5. Some parenchyma cells have many chloroplasts and
form the tissues found in leaves.
6. The chief function of this type of tissue is
photosynthesis, while parenchyma tissues
without chloroplasts are generally used for food
or water storage.
7. Parenchyma cells can divide if they are mature, and
this is vital in repairing damage to plant tissues.
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Parenchyma
collenchyma and
PARENCHYMA CELLS
COLLENCHYMA CELLS
80 m
Cortical parenchyma cells
sclerenchyma cells
SCLERENCHYMA CELLS
5 m
Sclereid cells
in pear
25 m
Cell wall
Parenchyma cells
Contain chloroplasts
60 m
Collenchyma cells
Fiber cells
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Collenchyma
 Have a living protoplasm, like parenchyma cells, and stay
alive for a long period of time.
 Their main distinguishing difference from parenchyma cells
is the increased thickness of their walls.
 LOCATION: just beneath the epidermis and generally they
are elongated and strong walls.
 As a plant grows these cells provide flexible support for
organs such as leaves and flower parts.
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Sclerenchyma
 These cells have thick, tough secondary walls
that are imbedded with lignin. At maturity, most
sclerenchyma cells are dead and function in
structure and support.
 Sclerenchyma cells can occur in two forms:
1. Sclereids:
 Randomly distributed
throughout other tissues.
 An example, the gritty
texture in some types of pears.
 Sclereids are sometimes called stone cells .
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2. Fibers
 are sometimes found in association with a wide
variety of tissues in roots, stems, leaves and
fruits.
 Usually are much longer than they are wide and
have a very tiny cavity in the center of the cell.
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Cells of different tissues
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Plant Growth
31.7 Primary growth lengthens roots and shoots
 Plant growth occurs at a region containing
embryonic tissue, which allows cell division
to occur (meristem)
 Meristematic tissue or meristem: is the type
of plant tissue which is composed of immature
cells and are always in a state of active cell
division producing new daughter cells
continuously.
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 Location: at the growing tips of roots,
stems and leaves.
 Cells of meristematic tissue helps to
increase the number of cells whereby
the overall plant growth occurs
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Meristems generate cells for new
organs
 A major difference between animals and plants is that
plants keep growing their entire life (indeterminate
growth) while animals stop growth once they reach a
certain size (determinate).
 Flowering plants can be categorized into 3 types based
on length of their life cycle (span):
1. Annuals: complete life cycle in 1 year i.e., herbaceous
plants: corn, geranium & marigold
2. Biennials: generally live 2 years herbaceous: i.,e carrot,
cabbage & foxglove.
3. Perennials: live many years. Herbaceous and woody
plants i.e., trees, Urginea maritima.
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(I) Classification according to origin:
(A) Primary meristematic tissue:
Remains meristematic from the embryonic
condition throughout entire plant life at the
growing apices of roots, stems, primordial of
leaves.
 Vascular cambium is also primary in nature.
(B) Secondary meristematic tissue
Gradually differentiated from primary meristems.
Examples include phellogen or cork cambium and
interfascicular cambium
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II) Classification according to position:
(A) Apical meristematic tissue
 Are located at the tips of roots and in the buds of
shoots
 Includes primary meristem.
 Elongate shoots and roots through primary growth
(B) Intercalary meristematic tissue
Merely parts of apical meristems that have become
separated from the apex and get surrounded by
permanent tissues.
Main function is increase in length of the axis.
Found in pulvini of grasses and leaf blades near
the basal parts.
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(C) Lateral meristematic tissue:
Present laterally or parallel to the sides of root
and stem.
Main role is to increase in diameter of plant
(woody plants) through secondary growth
(increase in girth)
Cambium and cork cambium are examples.
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Primary growth lengthens roots and shoots
 Primary growth produces the
primary plant body, the parts of
the root and shoot systems
produced by apical meristems
 Primary Growth of Roots
o The root tip is covered by a root
cap: which protects the delicate
apical meristem as the root pushes
through soil during primary
growth
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 The primary growth of roots:
– Produces the epidermis, ground tissue,
and vascular tissue
– Growth occurs just behind the root tip
in three zones;
1. Zone of division: root apical
meristem
2. Zone of elongation: responsible
for pushing tip further in the soil.
3. Zone of maturation: complete
their differentiation and become
mature.
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Organization of primary tissues in young roots
Epidermis
Cortex
Vascular
cylinder
Endodermis
Pericycle
Core of
parenchyma
cells
Xylem
100 m
(a)
Phloem
100 m
Transverse section of a typical root. In the
roots of typical gymnosperms and eudicots, as
well as some monocots, the stele is a vascular
cylinder consisting of a lobed core of xylem
with phloem between the lobes.
Endodermis
Pericycle
(b) Transverse section of a root with parenchyma
in the center. The stele of many monocot roots
is a vascular cylinder with a core of parenchyma
surrounded by a ring of alternating xylem and phloem.
Key
Dermal
Ground
Vascular
Xylem
Phloem
Figure 35.13a, b
50 m
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Lateral roots
 Arise from within the pericycle: the outermost cell layer in the
vascular cylinder
 Elongates and pushes through the cortex and epidermis until it
emerges
100 m
Emerging
lateral
root
Cortex
1
Vascular
cylinder
2
Epidermis
Lateral root
Figure 35.14
4
3
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Primary Growth of Shoots
o A shoot apical meristem
– Is a dome-shaped mass of
dividing cells at the tip of the
terminal bud
– Gives rise to a repetition of
internodes
and leaf-bearing nodes
– Leaves arise as
primordia
– Axillary buds can form
Lateral shoots.
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Tissue Organization of Stems
• In gymnosperms and most eudicots
– The vascular tissue consists of vascular bundles
arranged in a ring
Phloem
Xylem
Ground tissue
connecting
pith to cortex
Sclerenchyma
(fiber cells)
Pith
Key
Epidermis
Figure 35.16a
Vascular
bundle
Cortex
Dermal
Ground
1 mm
Vascular
(a) A eudicot stem. A eudicot stem (sunflower), with
vascular bundles forming a ring. Ground tissue toward
the inside is called pith, and ground tissue toward the
outside is called cortex. (LM of transverse section)
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• In most monocot stems
– The vascular bundles are scattered throughout the
ground tissue, rather than forming a ring
Ground
tissue
Epidermis
Vascular
bundles
1 mm
Figure 35.16b
(b) A monocot stem. A monocot stem (maize) with vascular
bundles scattered throughout the ground tissue. In such an
arrangement, ground tissue is not partitioned into pith and
cortex. (LM of transverse section)
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Tissue Organization of Leaves
1. The epidermal barrier in leaves
– Is interrupted by stomata: which allow CO2 exchange
between the surrounding air and the photosynthetic
cells within a leaf.
2. The ground tissue in a leaf
– Is sandwiched between the upper and lower
epidermis, a region called mesophyll
3. The vascular tissue of each leaf
– Is continuous with the vascular tissue of the stem, a
skeleton that reinforces the shape of the leaf
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Leaf anatomy
Guard
cells
Key
to labels
Dermal
Ground
Stomatal pore
Vascular
Cuticle
Epidermal
cell
Sclerenchyma
fibers
50 µm
(b) Surface view of a spiderwort
(Tradescantia) leaf (LM)
Stoma
Upper
epidermis
Palisade
mesophyll
Bundlesheath
cell
Spongy
mesophyll
Lower
epidermis
Guard
cells
Cuticle
Vein
Xylem
Phloem
(a) Cutaway drawing of leaf tissues
Guard
cells
Figure 35.17a–c
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Vein
Air spaces
(c) Transverse section of a lilac
(Syringa) leaf (LM)
Guard cells
100 µm
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31.8 Secondary growth increases the diameter
of woody plants
 Secondary growth occurs in stems (girth) and roots
of woody plants but rarely in leaves
 The secondary plant body consists of the tissues
produced by the vascular cambium and cork
cambium
Secondary
xylem
Secondary phloem
Late wood Vascular cambium
Early wood
Cork
cambium
Cork
Periderm
(b) Transverse section
of a three-yearold stem (LM)
Xylem ray
Bark
0.5 mm
Figure 35.18b
0.5 mm
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Cork Cambium and the Production of Periderm
 The cork cambium Gives rise to the secondary plant body’s
protective covering, or periderm
 Periderm Consists of the cork cambium plus the layers of
cork cells it produces
 Bark Consists of all the tissues external to the vascular
cambium, including secondary phloem and periderm
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 As a tree or woody shrub ages
– The older layers of secondary xylem, the heartwood,
no longer transport water and minerals
 The outer layers, known as sapwood
– Still transport materials through the xylem
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Reproduction of Flowering Plants
31.9 The flower is the organ
reproduction in angiosperms
 Flowers can vary greatly in shape
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sexual
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 All flowers contain four types of modified leaves
called floral organs:
1. Sepals: enclose and protect the flower bud, are
usually green and more leaf-like
2. Petals: often colorful and advertise the flower to
pollinators
3. Stamens
4. Carpels
are the reproductive
organs, containing the
sperm
and
eggs,
respectively
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 A stamen: consists of:
1. a stalk (filament)
2. anther: are sacs in which pollen is produced via
meiosis. Pollen grains house the cells that
develop into sperm.
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 A carpel has:
1. Stigma:
is the
platform for pollen.
landing
2. Style: a long slender neck
3. Ovary: the base of the carpel
which contains one or more
ovules, each containing a
developing egg and supporting
cells.
 The term pistil is sometimes
used to refer to a single carpel or
a group of fused carpels.
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The life cycle of a generalized angiosperm
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31.10 The development of pollen and ovules
culminates in fertilization
 The life cycles of plants are characterized by an
alternation of generations, in which haploid (n)
and diploid (2n) generations take turns producing
each other.
 The diploid plant body is called the sporophyte:
i.e., the roots, stems, leaves, and most of the
reproductive structures of angiosperms.
 sporophyte undergo meiosis to produce haploid
cells called spores.
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 Each spore then divides via mitosis and becomes
a
multicellular
gametophyte
(haploid
generation).
 Fertilization (male and
producing a diploid zygote.
female
gametes)
 The life cycle is completed when the zygote
divides by mitosis and develops into a new
sporophyte.
 In angiosperms, the sporophyte is the
dominant generation: It is larger, more obvious,
and longer-living than the gametophyte.
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Development of the male gametophyte
 Pollen grains are the male gametophytes are
found within a flower’s anthers
 Each cell undergoes meiosis, forming 4 haploid
spores.
 Each spore divides by mitosis, forming two
haploid cells: the tube cell and the generative
cell.
 The generative cell passes into the tube cell, and
a thick wall forms around them = pollen grain
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The development of female gametophyte = egg
 The ovary of a flower contains several ovules.
 The central cell undergoes meiosis, producing 4
haploid spores. Three of the spores degenerate
and one enlarges and divides by mitosis,
producing the embryo sac: is the female
gametophyte (eight-nucleate embryo sac).
 The sac contains a large central cell with two
haploid nuclei.
 One of its other cells is the haploid egg, ready to
be fertilized.
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Pollination
 The first step leading to fertilization is
pollination: the delivery of pollen from anther to
stigma.
 Vectors: insects mainly bees, birds, or other
animals insects, windborne (as anyone bothered
by pollen allergies knows).
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Pollen grain germination
 The pollen grain germinates on the stigma.
1. The tube cell gives rise to the pollen tube,
which grows downward into the ovary.
2. The generative cell divides by mitosis, forming
two sperm.
 The pollen tube discharges its two sperm near
the embryo sac:
1. One sperm fertilizes the egg, forming the
diploid zygote.
2. The other fuses to the large diploid central cell
of the embryo sac forming a triploid (3n)
nucleus, which give rise to a food-storing tissue
called endosperm. Al-Tardeh S.
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Double fertilization
 The union of two sperm cells with different
nuclei of the embryo sac is called double
fertilization.
 Endosperm (unique to angiosperms) will
develop only in ovules containing a fertilized
egg, thereby preventing angiosperms from
losing nutrients.
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31.11 The ovule develops into a seed
 After fertilization, the zygote divides by mitosis into
two cells and then produces a ball of cells that
becomes the embryo.
 The other cell divides to form a thread of cells that
pushes the embryo into the endosperm.
 The bulges you see on the embryo are the developing
cotyledons.
 Near the end of its maturation, the seed loses most of
its water and forms a hard, resistant seed coat
(brown)
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 The embryo, surrounded by its endosperm food
supply (gold), becomes dormant.
 Seed dormancy: a condition in which growth and
development are suspended temporarily, is a key
evolutionary adaptation.
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31.12 The ovary develops into a fruit
• While the seeds are developing from ovules,
hormonal changes triggered by fertilization
cause the flower’s ovary to thicken and
mature into a fruit.
• A fruit is a specialized vessel that houses and
protects seeds and helps disperse them from
the parent plant
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The changes in a pea plant leading to pod formation
1. Soon after pollination
2. The flower drops its petals, and
the ovary starts to grow. The
ovary expands tremendously,
and its wall thickens
3. forming the pod, or fruit, which
holds the peas, or seeds.
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Mature
either:
fruits can be
1. Fleshy: i.e., Oranges,
plums, and grapes, in
which the wall of the
ovary becomes soft
during ripening.
2. or dry: include beans,
nuts, and grains.
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31.13 Seed germination continues the life
cycle
 Germination: the plant resumes the growth and
development that were temporarily suspended
during seed dormancy.
 Germination usually begins when the seed takes
up water.
 Enzymes begin digesting stored nutrients in the
endosperm or cotyledons, and these nutrients
are transported to the growing regions of the
embryo
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 The hook protects the delicate shoot tip by holding it
downward, rather than pushing it up through the
abrasive soil.
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 A protective sheath (tunnel) surrounding the shoot
pushes upward and breaks through the soil.
 The corn cotyledon remains in the soil and
decomposes.
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31.14 Asexual reproduction produces plant
clones
 also called vegetative propagation.
 The resulting asexually produced offspring,
often called a clone, is genetically identical to
its single parent.
 Meristematic tissues can sustain growth
indefinitely. In addition, parenchyma cells can
divide and differentiate into the various types of
cells.
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Asexual reproduction in nature
 asexual reproduction involves
fragmentation:
the
separation of a parent plant
into parts that develop into
whole plants ie.e, garlic bulb.
 Each clove can give rise to a
separate plant. The white,
paper-thin sheaths are leaves
that are attached to the stem.
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Plants can also be asexually propagated in the
laboratory = plant cell culture
1. few meristem cells cut from a mature plant
2. cultured in a growth medium containing
nutrients and hormones.
 Using this method, a single plant can be
cloned into thousands of copies
 Is used to:
1. Produce plants used for mass plantings i.e.,
Orchids and certain pine trees
2. enable researchers to grow plants from
genetically engineered plant cells
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31.15 Evolutionary adaptations help some plants to
live very long lives
1. Adult trees, like most
adult plants, retain
meristems, which allow
for continued growth
and repair throughout
life.
2. Also, thick wood can
protect against insects
and disease.
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