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Plant Reproduction
Chapter 30
Impacts, Issues
Plight of the Honeybee
 Flowering plants coevolved with animal
pollinators such as honeybees – now pesticides
and other factors threaten our food supply
30.1 Reproductive Structures
of Flowering Plants
 Flowers are specialized reproductive shoots of
angiosperm sporophytes (diploid sporeproducing plant bodies that grow by mitotic cell
divisions of fertilized eggs)
 Spores that form by meiosis inside flowers
develop into haploid gametophytes (structures
in which haploid gametes form by mitosis)
Anatomy of a Flower
 Petals and other flower parts are modified
leaves that form in four spirals or whorls at the
end of a floral shoot
•
•
•
•
Calyx: A ring of protective sepals
Corolla: A ring of petals that attracts pollinators
Stamens: Male parts of a flower
Carpels (pistils): Female parts of a flower
Stamens
 Stamens consist of a filament with an anther at
the tip
 Anthers contain pollen sacs, in which diploid
cells produce haploid spores by meiosis
 Spores differentiate into pollen grains
(immature male gametophytes)
Carpels
 Flowers have one or several carpels, each with
a sticky stigma to capture pollen grains
 The ovary contains ovules which undergo
meiosis to form a haploid female gametophyte
 A diploid zygote forms when male and female
gametophytes join in an ovary
Structure of Flowers
Fig. 30-2a (1), p. 508
Fig. 30-2a (2), p. 508
stamen
(male reproductive part)
filament
anther
petal (all petals
combined are the
flower’s corolla)
sepal (all sepals
combined are
flower’s calyx)
carpel
(female reproductive part)
stigma
style
ovary
ovule
(forms
within
ovary)
receptacle
Fig. 30-2a (2), p. 508
Fig. 30-2b, p. 508
carpel structure
varies
ovary position
varies
ovule position
varies within
ovaries
Fig. 30-2b, p. 508
Animation: Flower parts
Typical Flowering Plant Life Cycle
germination
mature
sporophyte
(2n)
zygote
in seed (2n)
fertilization
DIPLOID
meiosis
in anther
meiosis
in ovary
HAPLOID
eggs (n)
sperm (n)
microspores
(n)
megaspores
(n)
male
gametophyte (n)
female
gametophyte (n)
Fig. 30-3, p. 509
germination
mature
sporophyte
(2n)
zygote
in seed (2n)
fertilization
meiosis
in anther
DIPLOID
meiosis
in ovary
HAPLOID
eggs (n)
sperm (n)
microspores
(n)
megaspores
(n)
male
gametophyte (n)
female
gametophyte (n)
Stepped Art
Fig. 30-3, p. 509
Animation: Flowering plant life-cycle
Animation: Eudicot life cycle
Diversity of Flower Structure
 Many variations in flower structure are
adaptations to maximize cross-pollination
•
•
•
•
Regular and irregular flowers
Single flowers and inflorescences
Complete flowers and incomplete flowers
Perfect flowers and imperfect flowers
Diversity of Flower Structure
30.2 Flowers and Their Pollinators
 Sexual reproduction in plants involves transfer of
pollen, usually from one plant to another
 Flowering plants coevolved with pollination
vectors (agents that deliver pollen from an
anther to a compatible stigma)
 Pollinators are living pollination vectors such as
insects, birds, or other animals
Flowers and Their Pollinators
 Flower shape, pattern, color and fragrance are
adaptations that attract specific animal pollinators
• Bees are attracted to bright white, yellow or blue
flowers, and patterns of UV reflecting pigments
• Bats and moths are attracted to certain scents
 Pollinators are often rewarded for visiting a flower
by obtaining nutritious pollen or sweet nectar
Flowers with Specific Animal Pollinators
Bees as Pollinators
Day and Night Pollinators
Attracting Pollinators
Animal Pollinator
30.1-30.2 Key Concepts
Structure and Function of Flowers
 Flowers are shoots that are specialized for
reproduction
 Modified leaves form their parts
 Gamete-producing cells form in their
reproductive structures; other parts such as
petals are adapted to attract and reward
pollinators
30.3 A New Generation Begins
 Male gametophytes form in pollen grains
• Diploid spore-producing cells form in pollen sacs
• Diploid cells undergo meiosis to form four haploid
microspores
• Mitosis and differentiation of microspores produce
pollen grains consisting of two cells
Female Gamete Production
 Female gametes form in ovules
• A mass of tissue (ovule) grows in an ovary
• One cell undergoes meiosis, forming four haploid
megaspores, three of which disintegrate
• One megaspore undergoes mitosis to form the
female gametophyte, which contains one haploid
egg, five other haploid cells, and one endosperm
mother cell with two nuclei (n + n)
Pollination
 Pollination occurs when a pollen grain arrives
on a receptive stigma and germinates
• One cell in the pollen grain develops into the
pollen tube, which grows toward the ovule
• The other cell undergoes mitosis to produce two
sperm cells (male gametes)
• A pollen tube containing male gametes
constitutes the mature male gametophyte
Fertilization
 Flowering plants undergo double fertilization
• Pollen tube releases sperm into the embryo sac
• One sperm cell fertilizes the egg, producing a
diploid zygote
• The other sperm fuses with the endosperm
mother cell, forming a tripod (3n) cell which is the
start of endosperm, a nutritious tissue that
nourishes the embryo sporophyte
Life Cycle: Eudicot
Fig. 30-8 (a-d), p. 512
pollen sac
anther
(cutaway
view)
filament
forerunner of
A Pollen sacs form in the
one of the
mature sporophyte.
microspores
Diploid Stage
meiosis
Haploid Stage
B Four haploid (n) microspores
form by meiosis and cytoplasmic
division of a cell in the pollen sac.
C In this plant, mitosis
of a microspore (with no
cytoplasmic division)
followed by differentiation
results in a two-celled,
haploid pollen grain.
Mature Male
Gametophyte
stigma
pollen tube
sperm cells
(male gametes)
D A pollen grain released from
the anther lands on a stigma and
germinates. One cell in the grain
develops into a pollen tube; the
other gives rise to two sperm
cells, which are carried by the
pollen tube into the tissues of
the carpel.
carpel
Fig. 30-8 (a-d), p. 512
pollen sac
anther
(cutaway
view)
filament
forerunner of
A Pollen sacs form in the
one of the
mature sporophyte.
microspores
Diploid Stage
meiosis
Haploid Stage
B Four haploid (n) microspores
form by meiosis and cytoplasmic
division of a cell in the pollen sac.
C In this plant, mitosis
of a microspore (with no
cytoplasmic division)
followed by differentiation
results in a two-celled,
haploid pollen grain.
Mature Male
Gametophyte
D A pollen grain released from
the anther lands on a stigma and
germinates. One cell in the grain
develops into a pollen tube; the
other gives rise to two sperm
cells, which are carried by the
pollen tube into the tissues of
the carpel.
stigma
pollen tube
sperm cells
(male gametes)
carpel
Stepped Art
Fig. 30-8 (a-d), p. 512
Fig. 30-8 (e-i), p. 513
ovary
wall
an ovule
cell
inside
ovule
tissue
seedling
(2n)
Sporophyte
seed coat
ovary (cutaway view)
embryo (2n)
endosperm seed
(3n)
double fertilization
Diploid Stage
meiosis
Haploid Stage
pollen
tube
endosperm
mother cell
(n + n)
I The pollen tube
grows down
through stigma,
style, and ovary
tissues, then
penetrates the
ovule and releases
two sperm nuclei.
E In a flower
of a mature
sporophyte,
an ovule forms
inside an ovary.
One of the cells
in the ovule
enlarges.
Female
Gametophyte
egg (n)
H Uneven cytoplasmic
divisions result in a sevencelled embryo sac with
eight nuclei—the female
gametophyte.
F Four haploid (n)
megaspores form
by meiosis and
cytoplasmic
division of the
enlarged cell.
Three megaspores
disintegrate.
G In the remaining
megaspore, three
rounds of mitosis
without cytoplasmic
division produce a
single cell that contains
eight haploid nuclei.
Fig. 30-8 (e-i), p. 513
ovary
wall
seedling
(2n)
an ovule
Sporophyte
cell
inside
ovule
tissue
seed coat
ovary (cutaway view)
embryo (2n)
endosperm seed
(3n)
double fertilization
Diploid Stage
Haploid Stage
pollen
tube
endosperm
mother cell
(n + n)
I The pollen tube
grows down
through stigma,
style, and ovary
tissues, then
penetrates the
ovule and releases
two sperm nuclei.
Female
Gametophyte
egg (n)
H Uneven cytoplasmic
divisions result in a sevencelled embryo sac with
eight nuclei—the female
gametophyte.
meiosis
E In a flower
of a mature
sporophyte,
an ovule forms
inside an ovary.
One of the cells
in the ovule
enlarges.
F Four haploid (n)
megaspores form
by meiosis and
cytoplasmic
division of the
enlarged cell.
Three megaspores
disintegrate.
G In the remaining
megaspore, three
rounds of mitosis
without cytoplasmic
division produce a
single cell that contains
eight haploid nuclei.
Stepped Art
Fig. 30-8 (e-i), p. 513
30.4 Flower Sex
 Recognition proteins on epidermal cells of the
stigma bind to molecules in the pollen grain coat
 Species-specific molecular signals from the
stigma stimulate pollen germination and guide
pollen-tube growth to the egg
 In some species, the specificity of the signal also
limits self-pollination
Pollen Tube Growth
30.3-30.4 Key Concepts
Gamete Formation and Fertilization
 Male and female gametophytes develop inside
the reproductive parts of flowers
 In flowering plants, pollination is followed by
double fertilization
 As in animals, signals are key to sex
30.5 Seed Formation
 After fertilization, mitotic cell divisions transform
the zygote into an embryo sporophyte
• Endosperm becomes enriched with nutrients
• Ovule’s integuments develop into a seed coat
 Seed (mature ovule)
• An embryo sporophyte and nutritious endosperm
encased in a seed coat
Seeds as Food
 As an embryo is developing, the parent plant
transfers nutrients to the ovule
• Eudicot embryos transfer nutrients to two
cotyledons, which nourish seedling sporophytes
• Monocot embryos use endosperm after
germination
 Humans also get nutrition from seeds (grains)
• Embryo (germ) contains protein and vitamins
• Endosperm contains mostly starch
Embryonic Development: Eudicot
Embryonic Development: Eudicot
Embryonic Development: Eudicot
Embryonic Development: Eudicot
many ovules
inside ovary
wall
embryo
endosperm
integuments
A After fertilization, a Capsella flower’s ovary develops into a fruit.
Surrounded by integuments, an embryo forms inside each of the ovary’s
many ovules.
Fig. 30-10a, p. 515
embryo
endosperm
B The embryo is heart-shaped when cotyledons start forming. Endosperm
tissue expands as the parent plant transfers nutrients into it.
Fig. 30-10b, p. 515
embryo
root apical
meristem
endosperm
shoot tip
cotyledons
C The developing embryo is torpedo-shaped when the enlarging
cotyledons bend inside the ovule.
Fig. 30-10c, p. 515
embryo
seed
coat
cotyledons
D A layered seed coat that formed from the layers of integuments surrounds
the mature embryo sporophyte. In eudicots like Capsella, nutrients have been
transferred from endosperm into two cotyledons.
Fig. 30-10d, p. 515
Animation: Eudicot seed development
30.6 Fruits
 As embryos develop inside the ovules of
flowering plants, tissues around them form fruits
 Fruit
• A mature, seed-containing ovary, with or without
accessory tissues that develop from other parts of
a flower
Fruit Development
tissue
derived from
ovary wall
carpel wall
seed
enlarged
receptacle
Fig. 30-11, p. 516
Mature Fruits
Seed Dispersal
 Fruits function to protect and disperse seeds
 Fruits are adapted to certain dispersal vectors
• Mobile organisms such as birds or insects
• Environmental factors such as wind or water
Adaptations for Fruit Dispersal
Three Ways to Classify Fruits
Stepped Art
Table 30-2, p. 517
Aggregate Fruits
30.5-30.6 Key Concepts
Seeds and Fruits
 After fertilization, ovules mature into seeds, each
an embryo sporophyte and tissues that nourish
and protect it
 As seeds develop, tissues of the ovary and often
other parts of the flower mature into fruits, which
function in seed dispersal
30.7 Asexual Reproduction
of Flowering Plants
 Vegetative reproduction
• Asexual reproduction in which new roots and
shoots grow from a parent plant or pieces of it
• Permits rapid production of genetically identical
offspring (clones)
Clones of Quaking Aspen
 Root suckers sprout after aboveground parts are
damaged or removed
Agricultural Applications
 Cuttings and grafting
• Offspring have the same desirable traits as the
parent plant
 Tissue culture propagation
• Cloning an entire plant from a single cell
 Seedless fruits
• Mutations that result in arrested seed
development or triploidy produce sterile fruit
Grafted Apple Trees
30.7 Key Concepts
Asexual Reproduction in Plants
 Many species of plants reproduce asexually by
vegetative reproduction
 Humans take advantage of this natural tendency
by propagating plants asexually for agriculture
and research
Animation: Apple fruit structure
Animation: Bee-attracting flower pattern
Animation: Double fertilization
Animation: Floral structure and function
Animation: Microspores to pollen
Animation: Pollination
Video: Imperiled sexual partners