28- Fungi Flashcards
Fungi
- “unified diversity”
- All are absorptive heterotrophs
- predators, parasites & mutualists (living tissues)
- saprobes (dead tissues) - All contain Chitin in cell walls
Yeasts
-Unicellular, free-living fungi
Multicellular filaments
(Vast majority)
-have hyphae, which are small filaments that grow through soil to form an interwoven mat called a mycelium
Chitin
- A strong, but flexible nitrogen containing polysaccharide
- forms the cell wall of fungi and the exoskeleton of Arthropoda
Mycelium
- fungal mat formed by hyphae
- increases surface area, for absorbing nutrients
Septate hyphae
- hyphae have cross walls (septa) that section off portions of the hyphae
- hyphae have pores for nutrients and organelles to move through (not nuclei)
Coencytic hyphae
- hyphae lack septa, so they are on mass of cytoplasm containing many nuclei
- results from mitosis but no cytokinesis
Decomposers
- leave behind organic materials that other organisms can use
- clean up dead organisms
Parasites
- produce specialized hyphae called haustoria
- branching projections that push through the cell walls of plants and extract nutrients
Pathogens
- Mycoses (infections from fungi)
- Pneumonia
- yeast infections
- ring worm and athletes foot
- Amphibian decline
- agricultural crop infections
Predators
-may posses looped hyphae that function as snares
Lichens
- not 1 organism, but a combination of a species of fungus, and either a Cyanobacteria or photosynthetic algae
- millions of of photosynthetic cells suspended in fungal mycelium
- Crustose (crust-like)
- foliose (leafy)
- fruiticose (shrub-like)
Mycorrhizae
-have mutualism with plants to exchange nutrients
*haustoria share nutrients instead of just extract like in parasites \
2 types…
Ectomycorrhizae
-fungus wraps around root tips (mass is often large)
-penetrates root and wraps around individual cells but does not go through their cell walls
(Short, swollen, and club-shaped)
Arbuscular mycorrhizae
- enter the root and penetrate cell walls of root cells, forming tree-like structures inside the cell wall, but outside the cell membrane
- greatly increase plants ability to absorb water and minerals
Fungal reproduction
- Both Sexual and Asexual
- spend most of their lives in an asexual state - Asexual:
- production of haploid spores within sporangium
- production of haploid spores at the tips of hyphae (Conidia in sac fungi)
- cell division by unicellular fungi
- mitotic growth and fragmentation of the mycelium
Sexual reproduction
- have mating types (instead of male and female), any two different types can reproduce
- hyphae from 2 different mycelia meet and release pheromones to determine if compatible
- if so, they fuse their hyphae (plasmogamy)
- nuclei pair up but do not fuse (heterokaryon)
- Dikaryotic state occurs when the nuclei pair off (two to a cell) but still do not fuse, only in Ascomycota and Basidiomycota
- nuclei from 2 mycelia then fuse (karyogamy)
- then immediately undergo meiosis to produce haploid spores
Diversity
-6 groups *likely paraphyletic
- Microsporidia
- Chytrids* (Chytridiomycota)
- zygospore* (zygomycota)
- Arbuscular Mychorrhizae (Glomeromycota)
- Sac Fungi (Ascomycota)
- Club Fungi (Basiodiomycota)
Microsporidia
- Unicellular (highly reduced)
- lack mitochondria, have mitosomes (no DNA in mitosome)
- Chitin cell wall
- obligate parasites
- have a “polar tube” which grows from the spore, which the fungi use to inject spore contents into host
Chytrids
- Decomposers and parasites
- early divergence from fungal ancestors,
- still have chitin cell wall, and some form hyphae in colonies - only fungi with flagellated zoospore gametes
Zygospore fungi
- decmoposers (molds), parasites, and commensal symbionts with animals
- have coencytic hyphae
- septa only found where reproductive cells form
Asexual Reproduction :
-forms sporangium to disperse haploid spores
Sexual Reproduction:
1) Hyphae from different mycelium form a zygosporangium, in which karyogamy and meiosis occur (can remain in this stage for a long time)
2) This zygospore then begins to sprout sporangiophores, which contain haploid spores
3) the haploid spores then turn into haploid hyphae
Glomeromycota
- almost all form arbuscular mycorrhizae
* 90% of all plant species form symbiotic relationships with glomerocetes
Dikarya
*when karyogamy occurs long after plasmogamy (n + n)
- 2 different haploid nuclei coexist & divide independently within each cell of a septate hyphae
- eventually produces a complex fruiting structure where karyogamy occurs in specialized cells
Ascomycota (sac-fungi)
- produce “ascospores” in sac-like “Asci” during sexual reproduction
- the asci are located in a fruiting body called an “Ascocarp”
-some are unicellular, but there are many elaborate multicellular structures (Morels,Truffles & cup fungi)
Asexual reproduction
-Budding
-or produce spores (conidia) at the tips of specialized hyphae (conidiophores)
Sexual Reproduction:
1) 2 hyphae of different mating strains fuse (plasmogamy)
2)forms dikaryotic cells with 2 haploid nuclei
3)cells at the tips of dikaryotic hyphae form asci which each contain 8 ascospores
*All formed within the ascocarp
Basidiomycota (club fungi)
- common fungi that decompose dead organisms material (mushrooms)
- some form mycorrhizae, and some are plant parasites
- The Basidium is the specialized cell in which karyogamy occurs
- a club-shaped cell where meiosis occurs to generate 4 haploid basiodiospores per basidium
Reproduction
- most reproduce only sexually, some have asexual cycles
- the long-lived dikaryotic mycelium produces a fruiting body called a basidiocarp (mushroom)
1) cytoplasm streams from dikaryotic mycelium to the tips of hyphae to form the basidiocarp
2) the basidiocarp produces many basidia on gills under the cap-like structures (each basidia carries out karyogamy)
3) each diploid nucleus resulting from karyogamy then divides meiotically to produce 4 haploid nuclei
4) each haploid nuclei is placed in an appendage to form 4 basidiospores
Usefulness of fungi
- Ecosystem nutrient cycling
- Food & drink production (baker’s/Brewer’s Yeast)
- defense against disease
- indicators of air quality (lichens)
- Remediation of pollution
- aid in reforestation
- model organisms for labs
