plant reproduction chapter 30. impacts, issues plight of the honeybee flowering plants coevolved...
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Plant Reproduction
Chapter 30
Impacts, IssuesPlight 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 spore-producing 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
Fig. 30-2a (2), p. 508
stamen carpel
(male reproductive part) (female reproductive part)
filament anther stigma style ovary
petal (all petals combined are the flower’s corolla)
ovule (forms within ovary)
sepal (all sepals combined are flower’s calyx)
receptacle
Fig. 30-2b, p. 508
Fig. 30-2b, p. 508
carpel structure varies
ovule position varies within
ovariesovary position
varies
Animation: Flower parts
Typical Flowering Plant Life Cycle
Fig. 30-3, p. 509
mature sporophyte
(2n)germination
zygote in seed (2n)
fertilization meiosis in anther
meiosis in ovary
DIPLOID
HAPLOID
microspores (n)
megaspores (n)
eggs (n) sperm (n)
male gametophyte (n)
female gametophyte (n)
zygote in seed (2n)
fertilization DIPLOID
Fig. 30-3, p. 509
mature sporophyte
(2n)germination
meiosis in anther
meiosis in ovary
HAPLOID
eggs (n) sperm (n)
male gametophyte (n)
female gametophyte (n) Stepped Art
microspores (n)
megaspores (n)
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
Fig. 30-8 (a-d), p. 512
pollen sac anther (cutaway view)
filament
forerunner of one of the microspores
A Pollen sacs form in the mature sporophyte.
meiosisDiploid StageHaploid 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.
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.
pollen tubestigma
Mature Male Gametophyte sperm cells
(male gametes)carpel
A Pollen sacs form in the mature sporophyte.
pollen sac anther (cutaway view)
filament
forerunner of one of the microspores
meiosisDiploid Stage
Fig. 30-8 (a-d), p. 512
Stepped Art
Haploid Stage
B Four haploid (n) microspores form by meiosis and cytoplasmic division of a cell in the pollen sac.
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.
pollen tube
stigmaMature Male
Gametophyte
carpelsperm cells (male gametes)
C In this plant, mitosis of a microspore (with no cytoplasmic division) followed by differentiation results in a two-celled, haploid pollen grain.
Fig. 30-8 (e-i), p. 513
Fig. 30-8 (e-i), p. 513
an ovuleovary wall
cell inside ovule tissueSporophyte
seedling (2n)
seed coatembryo (2n)
E In a flower of a mature sporophyte, an ovule forms inside an ovary. One of the cells in the ovule enlarges.
ovary (cutaway view)
seedDiploid Stage
double fertilization meiosisHaploid Stage
F Four haploid (n) megaspores form by meiosis and cytoplasmic division of the enlarged cell. Three megaspores disintegrate.
pollen tube
G In the remaining megaspore, three rounds of mitosis without cytoplasmic division produce a single cell that contains eight haploid nuclei.
Female Gametophyte
endosperm mother cell (n + n)
egg (n)
I The pollen tube grows down through stigma, style, and ovary tissues, then penetrates the ovule and releases two sperm nuclei.
H Uneven cytoplasmic divisions result in a seven-celled embryo sac with eight nuclei—the female gametophyte.
endosperm (3n)
Fig. 30-8 (e-i), p. 513
Diploid Stage
E In a flower of a mature sporophyte, an ovule forms inside an ovary. One of the cells in the ovule enlarges.
cell inside ovule tissue
an ovuleovary wall
ovary (cutaway view)
meiosis
Stepped Art
Haploid Stage
F Four haploid (n) megaspores form by meiosis and cytoplasmic division of the enlarged cell. Three megaspores disintegrate.
H Uneven cytoplasmic divisions result in a seven-celled embryo sac with eight nuclei—the female gametophyte.
Female Gametophyte
I The pollen tube grows down through stigma, style, and ovary tissues, then penetrates the ovule and releases two sperm nuclei.
endosperm mother cell (n + n)
pollen tube
egg (n)
G In the remaining megaspore, three rounds of mitosis without cytoplasmic division produce a single cell that contains eight haploid nuclei.
seed
double fertilization
seed coatembryo (2n)endosperm (3n)
Sporo-phyte
seedling (2n)
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
Fig. 30-10a, p. 515
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. 30-10b, 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. 30-10c, p. 515
root apical meristem
embryo
endosperm
shoot tip cotyledons
C The developing embryo is torpedo-shaped when the enlarging cotyledons bend inside the ovule.
Fig. 30-10d, p. 515
seed coat
embryo
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.
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
Fig. 30-11, p. 516
tissue derived from
ovary wall
carpel wall
seed
enlarged receptacle
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
Table 30-2, p. 517
Stepped Art
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