Feb 23, 2016
OH GOODNESS There is a fungus among
What is a fungus?
A eukaryotic, heterotrophic organism devoid of chlorophyll that obtains its nutrients by absorption, and reproduces by spores.
Characteristics 1. All are eukaryotic Possess membrane-bound nuclei (containing chromosomes)
and a range of membrane-bound cytoplasmic organelles (e.g. mitochondria, vacuoles, endoplasmic reticulum).
2. Most are filamentous Composed of individual microscopic filaments called hyphae, which exhibit apical growth and which branch to form a network of hyphae called a mycelium.
3. Some are unicellular e.g. yeasts. 4. Protoplasm of a hypha or cell is surrounded by a rigid wall Composed primarily of
chitin and glucans, although the walls of some species contain cellulose. 5. Many reproduce both sexually and asexually Both sexual and asexual
reproduction often result in the production of spores. 6. Their nuclei are typically haploid and hyphal compartments are often
multinucleate Although the Oomycota and some yeasts possess diploid nuclei. 7. All are achlorophyllous They lack chlorophyll pigments and are incapable of
photosynthesis. 8. All are chemoheterotrophic (chemo-organotrophic) They utilise pre-existing
organic sources of carbon in their environment and the energy from chemical reactions to sythesise the organic compounds they require for growth and energy.
9. Possess characteristic range of storage compounds e.g. trehalose, glycogen, sugar alcohols and lipids.
10. May be free-living or may form intimate relationships with other organisms i.e. may be free-living, parasitic or mutualistic (symbiotic).
Modes of nutrition Fungi=absorptive heterotrophs Animals=phagotrophic heterotroph Heterotroph (chemo-organotrophs):
an organism incapable of synthesizing carbohydrates from inorganic sources; requires preformed organic compounds produced by other organisms
Hyphae (singular, hypha) Cylindrical, branching filaments
composed of a tubular cell wall filled with cytoplasm and organelles
Most fungal hyphae are 2-10 m diameter
Septa Septa—regular cross-walls formed in
hyphae. Hyphae with septa are septate, those lacking septa are aseptate or coenocytic. primary septa are formed as a process of
hyphal extension and generally have a septal pore, which allows for cytoplasmic and organelle movement.
Secondary or adventitious septa are imperforate, formed to wall off ageing parts of the mycelium.
Fungi as model organisms Small genome relative to other
eukaryotes Many fungal genes are homologous to
those in other eukaryotes Easy to grow, short life cycles Haploid genomes amenable to mutation Sexual stage for analysis of segregation
and recombination of genes; all products of meiosis can be retrieved in haploid spores
Asexual (clonal) reproduction
Fungal Reproduction Many fungi have
the ability to reproduce by asexual and sexual means
Kingdom Fungi Phyla:
Chytridiomycota Form motile spores called zoospores Meiosis occurs in resting sporangium
Glomeromycota Form spores containing hundreds of nuclei; no known
sexual reproduction Zygomycota
Form asexual spores called sporangiospores Meiosis occurs in zygospore
Ascomycota (including Deuteromycetes) Form asexual spores called conidia Meiosis occurs in ascus
Basidiomycota Meiosis occurs in basidium
Fungal life cycles The vegetative thallus predominates in
the life cycle of a fungus The thallus may be haploid (1n),
dikaryotic (n+n) or diploid (2n) in different groups of fungi
Ploidy of thallus is determined by the timing of these events in the life cycle: Plasmogamy (cell fusion) Karyogamy (nuclear fusion) Meiosis (reduction division)
What are the 3 stages during the life cycle of the fungus?