Fungi Flashcards
Fungi
- Diverse: ~100,000 described species
- *Opisthokonts = closely related to animals & choanoflagellates
- Many ~multicellular or coenocytic
- many with large *fruiting bodies
- Almost all not phagotrophic; Instead, *Absorptive nutrition
Most described species are *terrestrial
- Important in decomposition
- Many parasites (or symbionts)
Fungi: more generalities
- Immotile: non-flagellated
- Most are filamentous: with *Hyphae
- mass of hyphae = ‘Mycelium’
With *cell wall; mostly the polysaccharide *chitin
- resistance to water stress: physical protection
- allows penetrative hyphal growth (via turgor)
Reproduction
- Asexual: especially by asexual *spores
- Reproductive structures making *sexual spores
Hyphae
- Branching filaments, typically a few micrometres wide
- Rapid growth
- Filamentous form gives a high surface area: volume ratio
- nutrient absorption
The growing hyphal tip
Absorption zone, then apical growth zone
- Secretory vesicles at end (expand tip membrane)
- Extension via *turgor pressure
- Cell wall
- Septa (partial separation)
Hyphae: coanocytic vs septate
- Coanocytic hyphae (multinucleate, one cell, doesn’t divide)
- Septate hyphae (partial with pores)
~cells: septa stop movement of large organelles, notably nuclei
‘Yeasts’
- Unicellular form of fungi: has evolved several times
- Most ‘bud’ when producing asexually
Nutrition and Metabolism
*Saprotrophs (saprophytes)
- Secrete ‘digestive’ (exo)enzymes
- ..then absorb resulting small organic molecules
Or directly absorb small organic molecules
- (e.g. if living on fruit**)
Most aerobic, but some are anaerobes or facultative anaerobes
Lifecycles and sex (in typical fungi)
- Lifecycle generally haploid-dominant (but note ‘dikaryon’ in ‘higher fungi’)
- Asexual reproduction widespread
- Sexual cycle involves fusion of compatible haploid hyphae (‘anastomosis’)
- Fusuin of nuclei (karyogamy) followed by production of ‘sexual spores’ by *meiosis
- (details vary by major group)
Asexual spores
- Small; made in large numbers
- Resist desiccation etc.
- For reproduction & dispersal
- e.g ‘Conidia’
Major types of fungi
- ‘Chytrids’ (unusual ‘hyphae’; different life cycles, inc. flagellated cells)
- Zygomycetes
- Glomeromycota **
- Ascomycota
- Basidiomycota
Zygomycetes
- Most filamentous: hyphae usually *coenocytic
- Many grow well on material rich in simple sugars: e.g. foodstuffs
Ascomycota & Basidiomycota
- Septate hyphae
Dikaryotic: - Fusion of hyphae (anastomosis) -> cells with *two haploid nuclei: (n + n ploidy; ‘dikaryon’)
- Extensive dikaryotic phase *before nuclei fuse to form a diploid state (Karyogamy)
Some better-known Ascomycetes
- Truffles, Morels
Most yeasts: - Saccharomyces
- Schizosaccharomyces
- Candida
Common & exploited moulds: - Penicillium
- Aspergillus
- Neurospora
- Pneumocystis
On Basidiomycota
- Dikaryotic mycelium can be extensive & long-lived before fruiting body forms
Fungi as decomposers on land
- Especially *plant material
- Many produce enzymes that degrade plant cell wall polymers:
- cellulose (usually cellulases), pectin, etc.
- ‘White-rot’ fungi (basidiomycetes, mostly) - main *lignin degrades
Symbiosis example: Mycorrhizae
- Mutualism between certain fungi & plant roots
- In >80% (!) of vascular plants
- 5000+ fungal species involved (not very specific)
Arbuscular mycorrhizae
The main type of ‘Endo mycorrhizae’
- (endo- ‘within’)
- Hyphae penetrate roto cell walls (but not cell membrane)
- ‘Arbuscules’: branched hyphae ends enhance contact with host
