OH GOODNESS There is a fungus among
us!!!!!!
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
Plants=autotrophs
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?