BIOL 226

• Fungi


  • Eukaryotes
  • Absorptive heterotrophs
  • Sexual and/or asexual reproduction
  • Haploid, primarily
  • Chitinous cell walls
• Fungus

  A monophyletic group of absorptive heterotrophic eukaryotes that have chitinous cell walls
• Major growth forms of fungi

  • Single-celled (yeasts) - reproduce through budding
  • Multicellular (molds) - reproduce through spores
• Hyphae

  • Filaments of cytoplasm and nuclei surrounded by cell wall
  • Septate hypha - separated into segments, reduces flow of cytoplasm
  • Coenocytic hypha - nuclei are free floating
• Other structures of fungi

  • Mycelium - feeding network of hyphae
  • Mushroom - reproductive structure
• Structure of fungi


  Relates to its function - network of thin hyphae = large surface area to volume ratio, well adapted to absorbing nutrients, leads to rapid growth from tips of hyphae
• Fairy rings


  1. A mycelium sends out a network of hyphae, which grows outwards

  2. The central hyphae dies over time, leaving the edges of the ring to form mushrooms
• Fossil evidence of fungi originating

  460 mya
• Fungi evolved from unicellular, flagellated protists
• Genetic evidence shows fungi and animals diverged ~1 bya
• Many fungi cannot fossilize very well, so the fossil evidence does not match the molecular evidence for when fungi and animals diverged
• Fungal life cycle


  • Haploid hyphae
  • 2-stage syngamy - fusion of two cells
  • Plasmogamy - cytoplasm fuses from parent mycelia, creates heterokaryon/dikaryon (n + n)
  • Karyogamy - fusion of nuclei, produces diploid cells
  • Immediate meiosis: restores the haploid condition
  • Spores - haploid cells that can produce a multicellular organism
• Heterokaryon and dikaryon


  Heterokaryon - two or more haploid nuclei

  Dikaryon - exactly two nuclei per cell

  Advantages: An individual is functionally diploid, getting benefits of the diploid state, able to produce genes from either nucleus, allows for genetic variability
• Ecological groupings of fungi

  • By form: molds, yeasts, lichens, mycorrhizae

  By lifecycle: decomposers, parasites, predator, mutualists
• Types of fungi


  • Chytrid fungi

  Zygomycetes

  Glomeromycetes

  Ascomycetes

  Basidiomycetes
• Chytrid fungi are the only group that have flagellated spores, found in lakes and soil, and can lead to the death of amphibians
• Zygomycetes are common molds with coenocytic hyphae, karyogamy occurs in zygosporangium, heterokaryon is within the resistant sporangium
• Glomeromycetes reproduce asexually, grow in plant roots, have a mutualistic relationship where the fungus brings nutrients to the plant and the plant provides carbs to the fungus
• Ascomycetes have a defining feature of producing sac-like structures, have a long dikaryotic stage which gives opportunities for genetic recombination
• Basidiomycetes produce fruiting bodies, can break down lignin, and are decomposers of wood, also have a long dikaryotic stage
• Plants

  Eukaryotic

  Multicellular

  Almost all autotrophic

  Have both chloroplasts and mitochondria

  Cell walls made of cellulose

  Earliest plants were terrestrial
• Other characteristics of plants

  • Capacity for sexual reproduction

  Alternation of generations - multicellular diploid and multicellular haploid stage

  Develop from embryos - diploid, multicellular structure enclosed in maternal tissue
• Plant


  Eukaryotic, photosynthetic organisms that develop from an embryo
• Alternation of generations


  Multicellular haploid and diploid forms

  Heteromorphic - diploid and haploid stages look different in plants

  Different structures involved in reproduction
• Plant life cycle


  Sporophyte - produces haploid spores

  Spores - produce haploid gametophyte

  Gametophyte - produces gametes which fertilize and form the zygote
• Aquatic vs terrestrial plant life

  Aquatic life is 3.9 billion years old (prokaryotes), terrestrial life is 500 million years old

  Terrestrial plants have derived traits like multicellular dependent embryos, multicellular gametangia, walled spores, apical meristems, and spatial separation of resources
• First colonizers of land were algae in littoral zones, selected for by periodic drying
• Major groups of plants

  • Nonvascular plants (bryophytes)

  Seedless vascular plants (e.g. ferns)

  Gymnosperms (non-flowering seed plants, e.g. conifers)

  Angiosperms (flowering plants)
• Bryophytes

  Colonized the land 475 mya, living descendants, live in moist habitats

  Adaptations: waxy cuticle, embryos, gametangia, apical meristems, resistant spores, most have stomata
• In bryophytes, the gametophyte is the dominant structure in the life cycle, sporophyte is dependent on the gametophyte
• Limitations of bryophytes for life on land: swimming sperm, no vascular tissues, no woody tissue
• Bryophytes provide critical ecosystem services: improve water quality, reduce flood risk, store carbon
• Vascular tissues in plants

  Allowed for the growth of larger and longer structures (stems, roots, leaves)

  Xylem - movement of water

  Phloem - movement of sugars
• Types of leaves


  • Microphyll leaves - unbranched vascular tissue

  Megaphyll leaves - branched vascular tissue
• Adaptations of seedless vascular plants

  • Xylem and phloem = vascular tissue

  Specialized tissue = roots and leaves

  Lignin = woody tissue

  Sporophyte becomes dominant
• Seedless vascular plants are found in moist habitats, limited by swimming sperm and fragile/independent gametophytes
• Coal forests were composed of seedless vascular plants, which caused global cooling due to high photosynthesis rates
• Seed plants

  Seeds: new dispersal structure, differ from spores

  Pollen: contains a reduced male gametophyte, reduction of the gametophyte
• Evolutionary trend is towards gametophyte reduction, from moss to flowering plants
• Female gametophyte of gymnosperms

  Two cones: female cone produces integument, inside is the megasporangium that produces the megaspore, which divides to form the female gametophyte (egg)