3.3: The Fungus Kingdom

  • 100 000 species
  • all are heterotrophic

Structures of Fungi

  • some are unicellular
    • yeasts
  • most are multicellular
    • structurally divers
  • hyphae
    • thread-like filament that makes up the basic structural unit of a fungus
  • mycelium
    • complex, net-like mass made of branching hyphae
    • live in soil or other nutritious substances
  • fruiting body
    • part of the fungus that is over the ground
    • spore producing reproductive structure

Fungal Nutrition

enzymes break down food externally and absorb food through cell membranes

Parasitic
  • absurd nutrients from living cells of host organisms
  • fungus lives inside host
  • ex: cordyceps invade insect body, insect dies and fungi emerge to produce new spores
Predatory
  • soil fungi
  • mycelia have specialized structures for trapping prey
  • ex: rings in hyphae of Arthrobotrys trap tiny worms called nematodes
Mutualistic
  • partnerships with other organisms
    • usually plants or protists
  • mycelia cover roots of plants
  • mycorrhiza
    • increase absorptive surface of plant roots, plant takes up more nutrients
    • fungus receives sugar from plant
Saprobial
  • saprobes are organisms that feed on dead organisms/organic waste
  • decomposers
    • mycelia absorb nutrients from dead/decaying organic matter
    • important role in recycling nutrients in ecosystems

Fungal Reproduction

  • asexual and sexual
Asexual Reproduction
  • budding
    • smaller cell develops while attached to parent cell
    • smaller cell is pinched off of the parent cell
    • unicellular yeasts
  • fragmentation
    • piece of mycelium breaks off and forms a new individual
  • spores
    • single celled from fruiting bodies
    • surrounded by a protective cell wall
    • most will not form new individuals
    • carried by wind or water to areas with life supporting conditions

Fungal Classification

  • classified based on reproduction and structure of fruiting body
  • asexual fungi in a single phylum
  • sexual fungi in four phyla
Fungi Imperfecti
  • do not reproduce sexually
  • diverse structures
  • ex: Cyclosporine is obtained from an imperfect fungus that lives in the soil
    • given to patients after transplant surgery to suppress immune systems
Chytrids (Phylum Chytridomycota)
  • unicellular
  • aquatic species, found in marine and freshwater ecosystems
  • spores have flagella
  • parasites
  • live on decaying plants or insects
  • ex: Synchytrium endobioticum
    • parasitic fungus
    • infects potato plants
    • causes potato wart, deforms potatoes
Zygospore Fungi (Phylum Zygomycota)
  • multicellular
  • mostly terrestrial
  • include common moulds
  • reproduce asexually in favourable conditions
  • sexually in unfavourable conditions
    • fungi produce zygospores
    • diploid structures that develop after two haploid hyphae of opposite types combine and fuse nuclei together
    • thick wall develops, protects contents from drying out
    • remains dormant until conditions are favourable for growth
    • absorbs water and nuclei undergo meiosis
Sac Fungi (Phylum Asocmycota)
  • largest group of fungi
  • fungi develop small finger-like sacs (asci) during sexual reproduction
  • obtain nutrients by breaking down materials in wood and bone
  • parasites of plants
    • produce leaf curl, chestnut blight, dutch elm disease
  • reproduction involves fusion of two mating types to form spore-bearing asci
  • includes single celled yeasts
    • cells usually reproduce asexually by budding
Club Fungi (Phylum Basidiomycota)
  • include mushrooms, puffballs, and stinkhorns
  • fruiting bodies release spores from club shaped hyphae (basidia)
    • basidiospores
  • some are parasites to plants
  • largest part of fungus is underground
    • network of hyphae

Lichens

  • composite organisms
    • form a unique organism that depends on a relationship between two other species
    • always consists of a fungus and a photosynthetic organism
  • live in harsh environments
  • important food source for animals
  • natural dye to colour wool and make litmus paper