2.Life cycle of angiosperm. Megagametogenesis: Ovule is where female gamete formation occurs. Megaspore mother cell (diploid); Megaspore mother cell undergoes meiosis to produce four haploid Megaspores; three megaspores degenerate and the one remaining megaspore divides by mitosis to form the Megagametophyte - embryo sac with 8 cells (3 antipodals, 2 synergids, 1 egg, and a polar nucleus (diploid)); Ovule has the embryo sac, two integuments, a nucellus, and a micropyle. Microgametogenesis: Male gamete formation occurs in the anther. Microspore mother cell (diploid); Microspore mother cell undergoes meiosis to produce four haploid Microspores; each microspore divides by mitosis to form a vegetative (pollen tube) and generative cell; the microgametophyte is the pollen grain.
3.Pollination of angiosperms is via wind, water or animal vectors. Abiotic = wind & water; biotic = animal-mediated. Pollination vs. Fertilization. Pollination involves different floral syndromes with each type of flower specifically adapted to a type of pollinator or a suite of pollinators.
4.Pollen germinates to grow a pollen tube down through the stigma and style to the ovary. Two sperm cells produced by each pollen grain. One sperm fuses with egg to produce zygote, the other fuses with the polar nuclei to produce the endosperm. Double fertilization.
5.Nutrient reserve of the angiosperm is either the endosperm or the absorbed endosperm (cotyledons).
6. Angiosperms have several differences from gymnosperms, which give them the advantage in terms of biodiversity.
7.Economic importance -- almost all of our food comes from angiosperms; horticulture; floriculture; medicines; building materials.