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Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 27
Plant Reproduction and
Development
(Sections 27.1 - 27.5)
Albia Dugger • Miami Dade College
27.1 Plight of the Honeybee
• Most food crops are flowering plants, which make pollen
• The recent decline of honeybees used to pollinate crops is a
huge threat to our agricultural economy
• pollinator
• An organism that moves pollen from one plant to another
Importance of Insect Pollinators
• Many plant species will not develop fruits (or only develop
inferior fruits) unless they receive pollen from other flowers
27.2 Reproductive Structures
of Flowering Plants
• Petals and other parts of a typical flower are modified leaves
that form in four spirals (whorls) at the end of a floral shoot
• flower
• Specialized reproductive shoot of an angiosperm
sporophyte
Flower Formation
• The outermost whorl develops into a ring of sepals (a calyx )
• Petals form in the second whorl (the corolla)
• A whorl of stamens (which produce male gametophytes)
forms inside the ring of petals
• The innermost whorl of modified leaves are folded and fused
into carpels (which produce female gametophytes)
Key Terms
• stamen
• Reproductive structure that produces male gametophytes
• In most plants it consists of a pollen-producing anther on
the tip of a filament
• carpel
• Reproductive structure that produces female
gametophytes
• Sticky or hairlike stigma together with an ovary and a style
Carpels
• Flowers may have one carpel, several carpels, or several
groups of carpels that may be fused
• A swollen region (the ovary) contains one or more ovules
• A cell in the ovule undergoes meiosis and develops into the
haploid female gametophyte
Key Terms
• ovary
• In flowering plants, the enlarged base of a carpel, inside
which one or more ovules form and eggs are fertilized
• ovule
• In a seed-bearing plant, a structure in which a haploid,
egg-producing female gametophyte forms
• After fertilization, matures into a seed
Anatomy of a Typical Flower
Anatomy
of a
Typical
Flower
stamen
filament anther
petal (all petals
combined are the
flower’s corolla)
sepal (all sepals
combined are
flower’s calyx)
carpel
stigma
style
ovary
ovule
(forms
within
ovary)
receptacle
Fig. 27.2a.2, p. 430
Flower Structure
• Flower structure varies
among different plant
species
Flower
Structure
carpel structure
varies
ovary position
varies
ovule position
varies within
ovaries
B Flower structure varies among
different plant species.
Fig. 27.2b, p. 430
Life Cycle of a Flowering Plant
• The life cycle of flowering plants is dominated by a diploid,
spore-producing sporophyte
• Spores that form by meiosis inside flowers develop into
haploid gametophytes, which produce gametes
• At fertilization, a diploid zygote forms when male and female
gametes meet inside an ovary
Life Cycle of a Flowering Plant
Life Cycle of a
Flowering
Plant
zygote
mature
sporophyte (2n)
in seed (2n)
microspores
(n)
sperm (n)
eggs (n)
male
gametophyte
megaspores
(n)
female
gametophyte
Fig. 27.3, p. 430
Life Cycle of a
Flowering
Plant
zygote
mature
sporophyte (2n)
in seed (2n)
microspores
(n)
sperm (n)
eggs (n)
male
gametophyte
female
gametophyte
megaspores
(n)
Stepped Art
Fig. 27.3, p. 430
Pollinators
• Sexual reproduction in flowering plants involves transfer of
pollen, typically from one plant to another
• Animal pollinators pick up pollen and transfer it to the flower
of a different plant
• A flower’s shape, pattern, color, and fragrance are
adaptations that attract specific animal pollinators
Coevolution
• ~90% of flowering plants have coevolved animal pollinators
• An animal’s reward for a visit to a flower may be nectar, oils,
nutritious pollen, or even sex
• Butterflies, hummingbirds, and honeybees feed on nectar
• Bats, moths, and flies are attracted to specific odors
• Some flowers have specializations that prevent pollination by
everything other than a specific pollinator species
Coevolution
• Zebra orchid mimics the
scent of a female wasp
• Female burnet moths
ready to mate
Key Concepts
• Structure and Function of Flowers
• Flowers are shoots that are specialized for reproduction
• Modified leaves form their parts
• Gamete-producing cells develop in their reproductive
structures
• Other parts such as petals are adapted to attract and
reward pollinators
27.3 A New Generation Begins
• In flowering plants, fertilization has two outcomes:
• It results in a diploid zygote, which becomes the mature
sporophyte
• It is the start of nutritive endosperm, which sustains rapid
growth of the sporophyte seedling until true leaves form
and photosynthesis begins
10 Steps in
the Flowering Plant Life Cycle
1. An ovule forms inside a flower’s ovary; one cell enlarges
2. Four haploid (n) megaspores form by meiosis and
cytoplasmic division of the enlarged cell
3. In one megaspore, three rounds of mitosis with no
cytoplasmic division result in a single cell with eight nuclei
4. Uneven cytoplasmic divisions result in a seven-celled
embryo sac (female gametophyte) with eight haploid nuclei
10 Steps in
the Flowering Plant Life Cycle
5. Pollen sacs form in an anther
6. Four haploid (n) microspores form by meiosis and
cytoplasmic division of a cell in the pollen sac
7. Mitosis and differentiation of a microspore produces a twocelled pollen grain, which enters dormancy, before being
released from the anther
Key Terms
• megaspore
• Haploid spore that forms in ovule of seed plants
• Gives rise to an egg-producing gametophyte
• microspore
• Walled haploid spore of seed plants
• Gives rise to a sperm-producing gametophyte
• dormancy
• Period of temporarily suspended metabolism
10 Steps in
the Flowering Plant Life Cycle
8. Pollen grains are released from the anther; one lands on a
stigma and germinates (pollination):
• One cell in the pollen grain develops into a pollen tube
• The other cell develops into two haploid sperm cells
9. The pollen tube grows down through tissues of the carpel,
carrying the two sperm nuclei with it
10 Steps in
the Flowering Plant Life Cycle
10. The pollen tube reaches the ovule, penetrates it, and
releases the two sperm nuclei (double fertilization)
• One sperm fertilizes the egg and forms a diploid zygote
• The other fuses with the endosperm mother cell, forming a
triploid (3n) cell which gives rise to triploid endosperm
Key Terms
• pollination
• Arrival of pollen on a receptive stigma
• double fertilization
• Mode of fertilization in flowering plants in which one sperm
cell fuses with the egg, and a second sperm cell fuses with
the endosperm mother cell
• endosperm
• Nutritive tissue in the seeds of flowering plants
Life Cycle of a Eudicot
Life Cycle of a Eudicot
1 An ovule forms
inside a flower’s
ovary. A cell in the
ovule enlarges.
an ovule
ovary
wall
seedling
ovary
seed
Sporophyte
(2n)
2 Four haploid (n) megaspores
form by meiosis and cytoplasmic
division of the enlarged cell.
Three megaspores disintegrate.
pollen
tube
sperm (n)
Meiosis
in ovary
endosperm
mother cell
(n + n)
egg (n)
10 The pollen tube reaches the ovule,
penetrates it, and releases the two sperm
nuclei. One nucleus fertilizes the egg. The
other fuses with the endosperm mother cell.
megaspores
(n)
3 In the remaining
megaspore, three
rounds of mitosis
with no cytoplasmic
division result in a
single cell with
eight nuclei.
Double fertilization
4
Uneven cytoplasmic divisions
result in a seven-celled embryo sac female
with eight haploid nuclei. This sac gametophyte
is the female gametophyte.
Fig. 27.5.1-4,10, p. 433
Life Cycle of
a Eudicot
pollen sac
anther (cutaway
view)
filament
5 Pollen sacs
form in an anther.
a cell in the pollen sac
Meiosis in
anther
6 Four haploid (n)
6
microspores
(n)
7 In this plant,
7
mitosis of a microspore followed by
differentiation
results in a twocelled pollen grain.
9 The pollen tube
grows down through
tissues of the carpel,
carrying the two
sperm nuclei with it.
8 Pollen grains are
8
pollen tube
sperm
cells
stigma
style
9
microspores form by
meiosis and cytoplasmic
division of a cell in the
pollen sac.
released from the
anther. One lands on a
stigma and germinates.
A cell in the grain
develops into a pollen
tube; the other, into two
haploid sperm cells.
mature male
gametophyte
Fig. 27.5.5-9, p. 432
Life Cycle of
a Eudicot
pollen sac
anther (cutaway
view)
filament
5 Pollen sacs
form in an anther.
a cell in the pollen sac
Meiosis in
anther
6 Four haploid (n)
6
microspor
es (n)
7 In this plant,
7
mitosis of a microspore followed by
differentiation
results in a twocelled pollen grain.
9 The pollen tube
grows down through
tissues of the carpel,
carrying the two
sperm nuclei with it.
8 Pollen grains are
8
pollen tube
sperm
cells
stigma
style
9
microspores form by
meiosis and cytoplasmic
division of a cell in the
pollen sac.
mature male
gametophyte
released from the
anther. One lands on a
stigma and germinates.
A cell in the grain
develops into a pollen
tube; the other, into two
haploid sperm cells.
Stepped Art
Fig. 27.5.5-9, p. 432
ANIMATION: Pollination
ANIMATION: Plant Life cycle
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27.4 From Zygotes to Seeds and Fruits
• After fertilization, mitotic cell divisions transform a zygote into
an embryo sporophyte encased in a seed
• As embryos develop inside the ovules of flowering plants,
tissues around them form fruits
• Water, wind, and animals disperse seeds in fruits
The Embryo Sporophyte Forms
• Double fertilization produces a zygote, which develops into an
embryo sporophyte, and a triploid (3n) cell, which develops
into nutrient-containing endosperm
• When the embryo matures, layers of integuments separate
from the ovary wall and become a protective seed coat
• The embryo sporophyte, its reserves of food, and the seed
coat become a mature ovule (seed)
A Seed
• seed
• Embryo sporophyte of a
seed plant packaged
with nutritive tissue
inside a protective coat
A Seed
root apical meristem
seed coat
embryo
shoot tip
cotyledons
Fig. 27.6, p. 434
Fruits
• Fruits include seed-containing “vegetables” such as beans,
tomatoes, grains, and squash
• Simple fruits(e.g. pea pod) form from a single ovary
• Aggregate fruits (e.g. strawberry) form from separate
ovaries of one flower
• Multiple fruits (e.g. pineapple) form from fused ovaries of
separate flowers
• fruit
• A seed-containing mature ovary of a flowering plant
• Often with accessory tissues
Parts of a Fruit
Parts of a Fruit
tissue
derived from
ovary wall
carpel wall
seed
enlarged
receptacle
Fig. 27.7, p. 434
Aggregate Fruits
Aggregate Fruits
Fig. 27.8a, p. 435
Aggregate Fruits
Fig. 27.8b, p. 435
Aggregate Fruits
Fig. 27.8c, p. 435
Categories of Fruits
• Based on tissues:
• True fruits develop from the ovary wall
• Accessory fruits include the ovary and other parts
developed from petals, sepals, stamens, or receptacles
• Based on appearance:
• Dry fruits (e.g. acorns, grains, strawberries)
• Fleshy fruits (e.g. cherries, berries, apples)
Function of Fruits
• The function of a fruit is to protect and disperse seeds
• Specific dispersal vectors are reflected in a fruit’s form:
• Water: Water-repellent outer layers
• Wind: Lightweight with breeze-catching specializations
• Animals: Hooks or spines that stick to feathers, feet, or fur
• Animal feces: Colorful, fleshy, fragrant fruits
Key Concepts
• Plant Sexual Reproduction
• In flowering plants, pollination is followed by double
fertilization
• After fertilization, ovules mature into seeds
• As seeds develop, tissues of the ovary and other parts of
the flower mature into fruits, which function to disperse
seeds
ABC Video: Doomsday Vault Seed Collection
Animation: Double Fertilization
27.5 Asexual Reproduction in Plants
• Most flowering plants can reproduce by vegetative
reproduction, a form of asexual reproduction that produces
genetically identical offspring
• Triploid species are sterile and can only reproduce asexually
• vegetative reproduction
• Growth of new roots and shoots from extensions or
fragments of a parent plant
Tissue Culture Propagation
• An entire plant may be cloned from a single cell with tissue
culture propagation
• This technique is used to improve food crops and to
propagate rare ornamental plants such as orchids
• tissue culture propagation
• Laboratory method in which body cells are induced to
divide and form an embryo
Key Concepts
• Asexual Reproduction of 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