BSC 116 Multicellular Eukaryotes
BSC 116 Multicellular Eukaryotes BSC 116
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This 5 page Class Notes was uploaded by Paola Araque on Friday January 29, 2016. The Class Notes belongs to BSC 116 at University of Alabama - Tuscaloosa taught by Dr. Cherry in Spring 2016. Since its upload, it has received 12 views. For similar materials see Principles Biology II in Art at University of Alabama - Tuscaloosa.
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Date Created: 01/29/16
Multicellular Eukaryotes: Fungi Plants (Part I) ● Multicellularity has arisen more than once. ○ multicellula: organisms occur in several clades ■ not the same as colonial groups! ● Fungi ○ heterotrophs with diverse ecological roles ○ heterotrophs; absorb nutrients without ingestion (parasitic) ○ secrete enzymes that break down many organic compounds (mutualists) ■ good decomposers ■ can be parasitic and pathogenic ■ can be mutualistic ● Fungi Body Structure ○ unicellular yeast ○ hyphae: multicellular filaments ■ mycelium: network of hyphae for the fungus. Makes it efficient to absorb the organic compounds they need. ○ chitin: some divided by septa ■ a) Septate hypha ■ b) Coenocytic hypha ● Fungi have important associations with plants. ○ Mycorrhizal fungi→plant mutualism ○ Fungi→P to plants; Plant→C to fungi ○ Ectomycorrhizae form sheath around and grow into extracellular spaces. ○ Arbuscular mycorrhizae use haustoria; forms arbuscules ● Fungi reproduce using spores produced both asexually and sexually ● Generalized life cycle: asexual reproduction ● Filamentous fungi produce spores (n) by mitosis (molds) ● Singlecelled yeasts that divide by mitosis or by budding. ● When the two mycelium come together from two different fungi, it gives sexual reproduction. ○ The pheremones attract mycelia to one another. ● Plasmogamy : cytoplasm of 2 mycelia fuseheterokaryon with 2 parental nuclei in 1 cytoplasm ● Karyogomy: 2 nuclei fuse→diploid (2n) zygote. ● Meiosis produce haploid (n) spores. Germination of new mycelium. ● Fungi evolved from singlecelled, flagellated protists: ○ DNA evidence suggests animals and fungi evolved independently from different protist ancestors. ○ Multicellularity arose independently in fungi and animals ○ Oldest fungi fossils: 460 million years ● 5 Clades of Fungi: ○ Chytrids, Zygomycetes, Glomeromycetes, Ascomycetes, Basidiomycetes ○ Chyatrids: ■ earliest branch; flagellzoospores ■ decomposers, parasites, and some mutualists ○ Zygomycetes: ■ can form zygosporangium in which karyogamy and meiosis occur. ■ decomposers (e.g black bread mold) ■ also parasites/commensals on animals ○ Glomeromycetes: ■ similar to zygomycetes, but most have arbuscular mycorrhizal associations with plants (>80% of plant species) ○ Ascomycetes sac fungi) ■ sexual spores formed iasci, wi ascocarps (fruiting bodies) ○ Basidiomycetes (club fungi) ■ sexual spores formed ibasidia, witbasidiocarps (fruiting bodies) ● Ascomycetes: ○ includes yeasts and multicellular fungi ○ some are mycorrhizae ○ 40% associate with green algae or cyanobacteria, folichens ○ Complex Life Cycles (Asexual) ■ asexual spores (conidia) produced on hyphae tips (conidiophores) ○ Plasmogamy: fusion of different mating types→dikaasci c ○ Karyogamy: occurs within each ascus→diploid zygote (2n) ○ Each zygote divides by meiosis→4 haploid nuclei (n) ○ Each haploid nucleus (n) divides by mitosascospores→dispersal. ● Basidiomycetes: ○ includes mushrooms, puffballs, shelf fungi ○ some are mycorrhizae ○ some plant parasites ○ important decomposers of wood. ○ Sexual Reproduction: ■ Plasmogamy→Dominant dikaryotic mycellium ■ Environmental cues→formation ofbasidiocarp ■ Basidiocarp gills lines with dikarbasida ■ Karyogamy: each basidium produces diploid nuclei (2n) ■ Each diploid nuclei divides by meiosis→basidium with 4 haploid nuclei (n)→basidiospore ■ Dispersal ● Harmful Fungi: ○ ⅓ of fungi parasites/pathogens ○ Plant parasites ■ Cryphonectria parasitica causes chestnut blight. ■ Parasites on crops ● decrease yields (1050% fruit lost per year) ● sometimes toxic to humans ○ Claviceps purpurea on rye, causinergotism if ingested. ○ Animal Parasites ■ skin (externamycosis: athlete’s foot, yeast infection, ringworm, etc. ■ systemic (internamycosis: can be caused by inhaled spores. ■ chytrids implicated in recent declines/extinctions of amphibians ● Helpful Fungi: ○ Mycorrhizae & lichens ■ mutualisms between phototrophs and heterotrophs ○ Ascomycete endophytes between leaf cells. ■ release compounds that protect plant from insects ○ food: mushrooms, truffles, cheeses, bread, beer ○ medicine: antibiotics and other drugs ○ bioengineering: fungi can make eukaryotic products that bacteria cannot. ● What is a Plant? ○ photosynthetic autotrophs ○ cell walls of cellulose ○ chloroplasts with chlorophylls a and b ● evolved from aquatic green algae (charophytes): shared derived traits ○ rings of cellulosesynthesizing proteins, flagellated sperm morphology, details of cell division ○ sporopollenin: tough outer coating of charophyte zygotes and plant spores ● Kingdom Plantae= Embryophytes ● Unique derived traits of land plants: ○ alternation of generations: multicellular sporophytes (2n) and gametophytes (n) ○ multicellular, dependent embryos ○ spororpollenin walled spores produced in sporangia ■ charophytes lack multicelled sporangia and no sporopollenin in their spores (only in zygotes) ○ multicellular gametangia ■ female= archegonia; male=antheridia ○ apical meristems: areas of growth on shoot and root tips. ○ other unique traits: waxy cuticle, stomata, mycorrhizal associations, secondary compounds. ● Use living (and fossil) plants to infer evolution: ○ traits of living plants and phylogenetic methods→order in which key traits appeared. ○ fossils (and molecular clocks) help us date clades ○ fossil spores from early land plants resemble sporebearing tissue in living plants ● vast diversity of living plants ● grouped into one of the 10 phyla ○ nonvascular (byrophytes) ○ vascular plants (seedless and seed plants) ● Major events in plant evolution: ○ multicellularity ○ invasion of land (about 475 million years ago) ○ origin of vascular tissue (about 420 million years ago) ○ appearance of (extant) seed plants (about 305 million years ago) ○ evolution of flowers (about 140 million million years ago) ● Earliest land plants lacked vascular tissue: ○ bryophytes: non vascular plants ■ three phyla: ● Hepatophyta (liverworts) ● Anthocerophyta (hornworts) ● Bryophyta(mosses) ○ Bryophyte Life Cycle: ■ haploid spores (n) develop protonemata ■ protonemata produce “buds” that undergo mitosametophores ■ sperm from male antheridi swims through moisture to reach the egg in the female gameophyte ■ fertilizatioccurs in female ■ archegonia➛zygote (2n) ■ gametophytes have male or female gametangia: ● antheridia➛male; produce flagellated sperm ● archegonia=female; produce eggs ■ zygote becomes sporophyte embryo ■ sporophyte grows long seta that emerges from archegonium; remains attached to gametophyte by foot ■ haploid spores (n) produced in capsule by meiosis➛dispersal of spores ● Five evolutionary innovations of vascular plants ○ vascular tissue: xyleto transport water; phloem to transport organic molecules ■ reinforced wilignin; allowed plants to get taller. ○ roots:organs to absorb water and nutrients from soul; not merely anchors. ■ allowed plants to get taller ○ leaves: increases surface area for photosynthesis ■ microphyll small, spine shaped (lycophytes) ■ megaphylls larger with highly branched vascular system ○ sporophylls:modified leaves bearing sporangia ■ many sporangia per plant ○ sporophytes dominate life cycles, with reductiongametophyte ● Seedless vascular plants: ○ Phylum Lycophyta, 1200 spp. ■ club mosses, spike mosses, quillworts ■ more ancient of the two phyla ○ Phylum, Pterophyta, 12,000 spp. ■ fern, horsetails, whisk ferns, etc. ■ more closely related to vascular plants; share derived characters related to leaf and root growth. ○ life cycles dominated by sporophyte stage ○ gametophyte is much smaller than sporophyte ○ sporophyte is not dependent on gametophyte.