Transcript Plants File
and Fungi Plants Fungi and Plants • • • • Structure Life cycles Major evolutionary trends Adaptations to terrestrial life Kingdom Plantae includes (red and) green algae and land plants Structure • Multicellular photosynthetic eukaryotes • Cellulose cell walls – unlike Eubacteria (peptidoglycan) or Fungi (chitin) • Chloroplasts – photosynthetic organelles Charophytes (green algae) presumed ancestor to plants • The move to land required many adaptations for terrestrial life • Focus on some of these adaptations in several groups of plants. • Place major changes on a phylogenetic tree to help organize this information Challenges to terrestrial life • Water conservation and distribution – On land water tends to run off and evaporate • Acquiring nutrients – On land, most nutrients below ground • Physical support – Air less dense, thus less buoyant • Dispersal of gametes and propagules – Swimming no longer effective Adaptations for water conservation and distribution: • • • • • • Vascular system with tracheids Waterproof leaves with waxy cuticle Roots Stomata Large size (low surface:volume ratio) Enclosed embryos Adaptations for nutrient collection: • Roots with fine root hairs to increase surface area Adaptations for physical support: • Roots – anchor plant to substrate • Vascular system with rigid lignin – Cylinders are strong, lightweight Adaptations for gamete and propagule dispersal • Pollen (and pollinators) • Seed dispersal (and dispersers) – Seeds enclose and nutritionally support developing gametophyte and embryo, so small gametophyte less likely to dry up Evolutionary trends in plants • See above adaptations to terrestriality • Also increased dominance of diploid (sporophyte) stage and reduction of haploid (gametophyte) stage Bryophyta – Mosses Example of non-vascular plant • Water conservation -- poor. Require moist habitat. – Waxy cuticle – Multicellular embryo enclosed in gametangia – No true leaves or roots – Resistant spores survive droughts – No vascular tissues • Nutrient collection – Tissues very thin – leaflike scales often only two cells thick, so absorb nutrients and water directly through surface • Physical support -- Generally very small, so little need for supporting structures. – Rhizoids for attachment only • Dispersal -- Still have swimming sperm, which need a layer of water on plant surface in which to swim to egg Bryophyta – Life cycle • Gametophyte (haploid) the dominant stage • Gametes formed in specialized structures on gametophyte (this is the green “mossy” part) – Sperm in antheridia, Eggs in archegonia • Sperm swims to archegonium and fuses with egg to form diploid zygote • Zygote grows mitotically to form the fruiting stalk (sporophyte) • Stays attached to gametophyte • Inside capsule, cells undergo meiosis to form haploid spores • Spores released, germinate to make new gametophyte Moss Life Cycle Liverworts: Phylum Hepaticophyta Hornwort: Phylum Anthocerophyta •Hornlike sporophytes have stomata Hornwort (Phaeoceros laevis) Credit: © Henry Robison/Visuals Unlimited Liverwort: Phylum Hepaticophyta Gemmae cups on the liverwort Marchantia. Credit: © Brad Mogen/Visuals Unlimited Moss: Phylum Bryophyta Credit: © Brad Mogen/Visuals Unlimited Seedless (spore-forming) vascular plants • • • • Phylum Lycophyta: club mosses Phylum Psilotophyta: whisk ferns Phylum Sphenophyta: horsetails Phylum Pteridophyta: ferns Vascular tissues • Tubes that allow terrestrial plants to grow larger than non-vascular plants can and to inhabit drier habitats. Formed of two types of tracheids • Xylem – dead cells joined end-to-end – transfer water and mineral nutrients up from the roots – Hard, woody (lignified) cells provide physical support • Phloem – live cells – transport photosynthate (sugars,etc) from leaves to rest of plant In seedless vascular plants: • First true roots specialized for obtaining water and nutrients from soil • Sporophyte is the dominant life stage, dwarfing the gametophyte • Still have swimming sperm so still dependent on water for sexual reproduction Representative life cycle: Ferns • Sporophyte, represented by the leaves or fronds on rhizome (underground stem with roots) • Sporophyte can produce haploid spores – by meiosis – in sporangia – Sporangia develop on underside of leaf in clusters called sori – the rusty brown spots you often see on fern leaves. • Spores germinate to form haploid gametophyte, which is a very small prothallus – relatively undifferentiated tissue • Gametophyte produces eggs and flagellated sperm, which swim to eggs • Diploid zygote germinates into sporophyte right in archegonium of gametophyte Fern Life Cycle Characteristics of Phyla • Phylum Psilotophyta-- Whisk ferns -- no leaf blades Phylum Lycophyta -Club mosses and ground pines doooddoo • Scale-like leaves • Extant species mostly small Credit: © Charles McRae/Visuals Unlimited • Lepidodendron Ancient giant club moss was up to 40 m tall! Phylum Sphenophyta -Horsetails • One extant genus -Equisetum • Hollow, jointed stems contain silica (glass) rough texture • Whorls of stems with tiny leaves at base Credit: © David Sieren/Visuals Unlimited Sphenophyta -Horsetails • Calamites, extinct horsetail, is important in coal deposits, was tall as many modern trees, up to 20 m Ferns: Phylum Pteridophyta: fronds usually begin as “fiddleheads” Gymnosperms: Naked-seeded vascular plants • Phyla Coniferophyta , Cycadophyta, Ginkgophyta, and Gnetophyta • Female gametophyte retained within sporophyte – Gametophyte no longer as susceptible to desiccation, no matter how small it is. – Can be nourished as well as protected by surrounding tissue Pollen • Microspore develops into pollen grain –Has a few haploid nuclei. –Small, desiccation resistant, enclosed male gametophyte can disperse on wind (the original "Air Male"?) –No longer needs water for dispersal of sperm or fusion with egg, sperm no longer swims Seed • Multicellular sporophyte embryo • Plus food supply • Inside desiccation-resistant seed coat • Dispersal adaptations in some (wings, hooks, etc) Life cycle, illustrated by conifer • Staminate (male) pollen cones and ovulate (female) seed cones produced • Haploid male gametophyte forms pollen grains with a few nuclei each • Pollen is shed and dispersed by wind. • Lands on female cone (pollination) • Pollen tube grows toward ovum • One nucleus in pollen grain divides mitotically to form two nuclei • Nucleus travels down pollen tube, where nonflagellated sperm fertilizes egg • After fertilization, embryo (diploid sporophyte) begins to develop, as does food supply from female • Resulting seed is released, disperses, germinates, and develops into mature sporophyte. Pine Life Cycle Cycadophyta: Cycads • Palm-like, • compound leaves • usually with terminal cones • Zamia integrifolia Ginkgophyta • Ginkgo biloba --only extant species of Ginkgophyte -- Fan shaped leaves Coniferophyta: Conifers • Cones, needle or scale-like leaves Gnetophyta -- 3 Extant genera • Welwitschia -- bizarre taproot with 2 giant leaves • Gnetum -- Resembles flowering plants in many respects -- e.g., double fertilization • Ephedra --"Joint fir" or “Ma huang” source of decongestant ephedrine Welwitschia Tree (Welwitschia mirabilis), 1000 years old. NamibNaukluft Park, Namibia. Credit: © Joe & Mary Ann McDonald/Visuals Unlimited 306427 Credit: © Science VU/Visuals Unlimited Gnetum gnemon. 300667 Credit: © Gerald and Buff Corsi/Visuals Unlimited Mormon Tea (Ephedra viridis) Gymnosperms & Angiosperms Seeds Exposed / on cone scales Woody tree/shrub Within fruit Reproductive structure Cone (usually) Flower Pollen grain dispersal Wind Animals or wind Fertilization Egg + sperm = zygote Double fertilization: (Double fertilization in Egg + sperm = zygote some gnetophytes) 2 polar nuclei + sperm = endosperm Growth habit Woody or herbaceous Angiosperms -- Flowering plants -Phylum Anthophyta • Flowers = specialized organs to facilitate pollination by animals Symbiosis of flowering plants and pollinators ensures efficient fertilization • Flowers generally provide a nectar reward to entice pollinators to visit • Pollinators incidentally pick up pollen in the process of feeding and deliver to next flower they visit • Flowering plants and insects are the two most diverse taxa on the planet! Flower parts are modified leaves • Homology suggests descent with modification • Sepal, petal = 2 outermost leaflike parts • Male structures = Stamens – Composed of pollen-bearing anther held on filament • Female structures = Pistils – Stigma = sticky part for collecting pollen – Style = shaft – Ovary contains one or more ovules, each of which contains one egg Fruit = mature ovary surrounding seed • Fleshy, nutritious fruits are specialized organs for seed dispersal by animals • Like nectar, fruit is the reward • Seeds are dropped or incidentally ingested and passed in feces later Double fertilization • BOTH sperm participate in fertilization • One sperm fuses with the egg • Other fuses with the two haploid polar nuclei of the central cell to form a 3n (triploid) cell • The 3n cell undergoes mitosis to generate the endosperm, which is a nutritive tissue for the seed • This process found only in flowering plants and two gymnosperms: discovered in 1990 in Ephedra nevadensis and Gnetum gnemon in 1996 Fungi and Plants • • • • Structure Life cycles Major evolutionary trends Adaptations to terrestrial life