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) carpel (female reproductive part) filament anther stigma style ovary petal (all petals combined are the flower s corolla) sepal (all sepals combined are flower s calyx) 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 HAPLOID meiosis in anther meiosis in ovary 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 DIPLOID HAPLOID meiosis in anther meiosis in ovary 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 meiosis forerunner of one of the microspores Diploid Stage Haploid Stage A Pollen sacs form in the mature sporophyte. 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) carpel 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. Fig. 30-8 (a-d), p. 512
pollen sac anther (cutaway view) filament meiosis forerunner of one of the microspores Diploid Stage Haploid Stage A Pollen sacs form in the mature sporophyte. 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) carpel 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. Stepped Art Fig. 30-8 (a-d), p. 512
Fig. 30-8 (e-i), p. 513
seedling (2n) Sporophyte seed coat embryo (2n) endosperm (3n) double fertilization seed ovary wall ovary (cutaway view) Diploid Stage Haploid Stage an ovule meiosis cell inside ovule tissue E In a flower of a mature sporophyte, an ovule forms inside an ovary. One of the cells in the ovule enlarges. 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. pollen tube egg (n) Female Gametophyte 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
seedling (2n) Sporophyte seed coat embryo (2n) endosperm (3n) double fertilization seed ovary wall ovary (cutaway view) Diploid Stage Haploid Stage an ovule meiosis cell inside ovule tissue E In a flower of a mature sporophyte, an ovule forms inside an ovary. One of the cells in the ovule enlarges. 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. pollen tube egg (n) Female Gametophyte 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. 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