Alternation of Generations Haploid (n) plant reproduction chapter 38 Diploid (2n) Sporangium Spore dispersal Spore (n) Young Mature (n) ARCHEGONIUM ANTHERIDIUM Sperm Mature Sorus Sporangium sporophyte (2n) New sporophyte Zygote (2n) Gametophyte Fiddlehead angiosperms sporophyte larger and nutritionally independent produces spores by meiosis. gives rise to gametes by mitosis. pollen grain is the male Sexual Reproduction? - the flower produce s, attract s, and develop seeds. flowers reproduce asexually, and then facilitate sexual reproduction POLLINATION Mitosis: division of the nucleus resulting in an exact copy of the original Meiosis: reduction in the number of chromosomes. Gametogenesis: Formation of sperm and eggs. Fertilization: fusion of sperm and egg.
flowers flowers floral anatomy arranged in whorls or circles of structures: Sepals, petals, stamens, and carpels. receptacle calyx corolla corolla stamens filament and an anther Each pollen grain contains two cells; germinative vegetative Stamen Filament Anther Petal Sepal Receptacle calyx pollen flowers pollen production each diploid cell produces 4 microspores. 4 microspores > 4 pollen grains generative cell - sperm nuclei vegetative cell - pollen tube surrounding pollen grain outer layer - sporopollenin inner layer - pectin surround Microsporangium (pollen sac) Generative cell (n) Microsporocyte (2n) 4 microspores (n) Each of 4 microspores (n) MITOSIS Male carpels (pistils) - style and stigma ovary contains 1+ ovules. ovule produces/contains embryo sac. embryo sac - 2 polar nuclei and 1 egg. Stigma Carpel Style Ovary 20 µm Nucleus of tube cell (n) Receptacle 75 µm Ragweed pollen grain
embryo sac female. ovule inner tissue = nucellus 1-2 protective layers = integuments 1 diploid cell in nucellus produces 4 haploid cells 3 mitotic divisions polar nuclei, egg, synergids, antipodals MITOSIS Integuments (2n) 100 µm Megasporangium (2n) Megasporocyte (2n) Integuments (2n) Micropyle Surviving megaspore (n) 3 antipodal cells (n) 2 polar nuclei (n) 1 egg (n) 2 synergids (n) Embryo sac Female floral structure Variations Arrangement of floral parts: spiral or whorled. Floral whorls: Complete carpels and stamens: Perfect Imperfect carpellate or staminate Sex of the plants: Hermaphroditic monoecious dioecious "Oikos" = house sex of plants hermaphroditic (flowers perfect) monoecious (staminate and carpellate flowers) (staminate flowers) dioecious (carpellate flowers) complete perfect (hermaphroditic) incomplete monoecious dioecious imperfect
fertilization Stigma fertilization Some can self-fertilize Other cannot self-fertilize -- self-incompatible Fertilization pollen tube generative cell divides to form 2 sperm nuclei endosperm ovule --> seed ovary --> fruit Pollen grain 2 sperm Style Ovary Micropyle Polar nuclei Synergid 2 sperm nucleus (3n) (2 polar nuclei seed development Pollen tube Polar nuclei 3N nucleus mitosis large multinucleate cell. cells develop cell wall endosperm becomes solid. Seed coat Seed coat Cotyledons (b) Castor bean, a eudicot with thin cotyledons Scutellum (cotyledon) Coleoptile plus sperm) Coleorhiza (c) Maize, a monocot Zygote (2n) (egg plus sperm) fruits aggregate fruits made up of multiple ovaries multiple fruits made up of more than one flower achene dry pericarp seed dispersal benefits reduced competition between offspring for resources decreased relatedness to potential mates reduced competition between parent and offspring agents of seed dispersal Cotyledons (a) Common garden bean, a eudicot with thick cotyledons mature embryo cotyledons radicle hypocotyl epicotyl plumules Pericarp fused with seed coat
pollination pollination coevolution - animal pollinators Asexual reproduction vegetative reproduction no fusion of gametes. Stems, leaves and roots. Apomixis - like parthenogenesis fragmentation - stems, leaves Roots can produce aerial shoots many flowers are wind pollinated