5 derived characteristics in land plants (not in ancestors) • Apical meristems – localized areas of cell division in shoot & tips • Alternation of generations – separate slide • Walled spores produced in sporangia • tough wall resists drying • 2n spore mother cells go through meiosis to produce 4 haploid spores • Multicellulargametangia • Archegonium – (female) produces haploid egg & keeps it • Antheridium – (male) produces & releases sperm • Multicellular, dependent embryos • develop w/in archegonium from zygote • Derive nutrition from female parent tissue with specialized placenta-like cells
2 more traits that evolved in many plant groups • Cuticle • Made of waxes on surface of epidermal cells • Protection • Secondary compounds • Repel herbivores & parasites • Absorb UV radiation • Attract symbionts
4 Major Plant Phyla Bryophytes Pterophytes Gymnosperms Angiosperms nonvascular plants Bryophytes (mosses) Land plants vascular plants Seedless Pterophytes (ferns, etc) Seed plants Naked seeds – Gymnosperms Coniferophyta Enclosed seeeds – Angiosperms Anthyophyta
Bryophytes • Non-vascular – whole body can absorb water • Gametophyte is larger (dominant) stage • Sporophyte dependent on gametophyte • No true leaves • Flagellated sperm • Mosses require water for fertilization. Why?
Pterophytes • Seedless vascular plants • Ex – ferns • Sporophyte larger stage • True roots & leaves w/ horizontal stem • Sporangia on leaves called sporophylls • Homosporous – one kind of spore (bisexual gamete – egg & sperm) • Heterosporous • female spore (megaspore) female gametophyte egg • Male spore (microspore) male gametophyte sperm
Vascular Seed Plants • Common traits • Seeds • Integument – seed coat • Female gametophyte – food supply • Embryo sporophyte – baby plant • Advantage of seeds • Consists of embryo and food supply contained in protective coat • Better resist harsh environments • Disperse offspring more widely
Reduced gametophytes – spores retained in sporangia, develop into gametophytes • Heterospory – • Megasporangium produce one megaspore & female gametophyte • Microsporangium produce many microspores & male gametophytes • Ovules – contains female gametophytes • Pollen – contain male gametophytes – transferred to female part of plant and will germinate into a pollen tube that finds the ovule and egg
Gymnosperms • Bear “naked” cones – seeds are exposed on modified leaves that usually form cones • Pollen cones – produce pollen • Ovulate cones – produce eggs • Coniferophyta – pines, firs, redwoods
Angiosperms • Anthophyta - Flowering plants used for sexual reproduction • Megasporangium megaspore megagametophyte in ovule (all enclosed in ovary of flower) • Microsporangium microspore microgametophyte in anther of flower • Fruits - mature ovary – seed develops from ovules after fertilization, the wall of the ovary thickens • Ex – tomato, grapefruit, nectarine, milkweed, walnut • Pollination required for transfer of pollen from flower to the female sex organs of another flower
Double Fertilzation • One sperm fertilizes the egg cell and the other sperm combines with the two polar nuclei of the large central cell of the embryo sac. Result - One sperm nucleus unites with the egg to form the diploid zygote, from which the embryo develops, and the other unites with two polar nuclei to form the triploid, primary endosperm nucleus (nutrition).
Seeds – monocots& dicots DICOT DICOT MONOCOT
Germination • Imbibation – taking in H2O • ABA decreases (plant soluble hormone that causes dormancy) • Embryo responds and releases gibberellin (stimulates release of amylase) • Amylase breaks down starch for nutrition which allows for growth • Root extends downward while shoot extends upward
Factors affecting germination – HOW? • Water • Oxygen • Temperature • Light