Fungi

Question 1

Origins of fungi

Answer 1

Pre-Cambrian - based off fossil evidence
760 million – 1.06 billion years
More closely related to animals
> 100, 000 species identified
Colonise a range of habitats

Question 2

Defining characteristics of fungi

Answer 2

Eukaryotic
- Membrane-bound nuclei
- Membrane-bound organelle
Typically have a haploid genome
- Several nuclei within each hyphae
- Many budding yeasts are diploid
Produce spores
- Reproduce sexually and asexually
- Vary in size and shape
Heterotrophic – they depend on pre-formed organic nutrients
Typically grow as hyphae, with apical growth, but sometimes as yeasts
Have cell walls composed primarily of chitin and glucans
Absorb soluble nutrients through the cell wall and plasma membrane

Question 3

Fungi growth

Answer 3

Vegetative body is a unicellular or multicellular thallus
Unicellular fungi = yeasts
Most are multicellular
Display two distinct morphological stages:
- vegetative
- reproductive
Vegetative stage consists of thread-like structures calledhyphae
Mass of hyphae = mycelia
Hyphae have a tubular structure, and those tubes can be divided by cross walls called septa

Question 4

Septa

Answer 4

Perforations in septa allow nutrients to move from cell to cell along the hypha
Ascomycetes – simple pore
- Woronin bodies - membrane bound proteinaceous organelles that can block pores
Basidomycetes – dolipore
- Parenthesome - allows for cytoplasmic continuity but blocks movement of large organelles

Question 5

Fungi nutrition

Answer 5

Use complex organic compounds as a source of carbon
Do not fix nitrogen from the atmosphere
Digestion precedes ingestion
Exoenzymes transported out of the hyphae = process nutrients
Glycogen - storage

Question 6

Special structures of fungi

Answer 6

Appressoria (sing. = appresorium), penetration structure
Haustoria (sing. = haustorium), specialised hyphae
Rhizomophs = mycelia cords
Chlamydospores = spores within hyphae
Sclerotia = asexual, dormant resting body

Question 7

Life habitats

Answer 7

Parasite/pathogen
- Disease causing agent
Symbiont
- Forms associations with other organisms
Saprotroph
- Gains nutrients from non-living materials

Question 8

Fungal pathogens of plants

Answer 8

Obtain nutrients from the living tissues of their host
Can be host specific
Fusarium oxysporum f.sp
Biotrophic – feed without killing
Necrotrophic – aggressive, kill the host
- Toxins or degradative enzymes

Question 9

Fungal pathogens of humans

Answer 9

~200 species that infect humans
Infections can be:
- mycosis= infection and direct damage
- mycotoxicosis= poisoning by contaminated food
- Allergies
- Opportunistic
Immuno-compromised
- AIDS
- Transplant patients
- Cancer
- Diabetes
- Corticosteroid therapy
Dermatophytic fungi
- Skin, nail and hair infection

Question 10

Fungal pathogens of insects

Answer 10

Example Ophiocordyceps unilateralis
discovered by the British naturalistAlfred Russel Wallacein 1859
Fungus results in alteration of the behavioural patterns of the infected ant
Fungus then kills the ant and continues to grow as its hyphae invade more soft tissues

Question 11

Fungal symbionts of plants

Answer 11

Mycorrhiza
- Associations between fungi and roots
- Fungi dependent upon plant for carbon
- Plant dependent upon fungi for phosphorus, nitrogen etc
- Arbuscular mycorrhiza – hyphae penetrate the root cells
- Ectomycorrhiza – hyphae do not penetrate the root cells
Lichens
- Photosynethetic partner (algae/cyanobacterium) and fungi
Endophytes
- Do not harm the plant
- May activate plant defence genes
- Produce anti-feedants e.g. ergot alkaloids

Question 12

Fungal animal mutualism

Answer 12

Fungus provides protection
Insect provides nutrients
Leaf cutter ants and fungi farm
Fungi digest cellulose in the leaves
Ants feed off the fungi and protect fungi from competing fungi

Question 13

Fungal saprotrophs

Answer 13

Feed on dead organic matter
Important role in decomposition
- Starch, cellulose, proteins, chitin, keratin and lignin
Recycling major nutrients
Significant spoilage agents
- Dry-rot
- Sooty moulds
Mycotoxins

Question 14

Classification

Answer 14

Eight main phyla within the Kingdom Fungi
Basidiomycota (mushrooms, rusts, smuts, etc.)
Ascomycota (sac fungi, yeast, Penicillium, etc.)
Glomeromycota (arbuscular mycorrhizal fungi)
Zoopagomycota (parasites and commensals)
Mucoromycota (rhizosphere competent or decomposers)
Blastocladiomycota (aquatic fungi – zoosporic fungi)
Chytridiomycota (Zoosporic fungi)
Cryptomycota (Zoosporic fungi)
Microsporidia (Zoosporic fungi)

Question 15

Fungi-like organisms

Answer 15

Oomycota
- Potato blight Phytophthora infestans
- Water mould Saprolegnia
- Downy mildew Peronospora farinosa
- Root rot Pythium sp.
- Slime moulds
Classified as Protists

Question 16

Fungal reproduction

Answer 16

Asexual reproduction
Reproduce asexually by: Fragmentation, budding or producing spores
Fragments of hyphae can grow new colonies
Somatic cells in yeast form buds
Most common mode is formation of asexual spores – genetically identical to parent

Question 17

Sexual reproduction in fungi

Answer 17

1.Cell fusion - Plasmogamy between two haploid cells = two different haploid nuclei
2. Nuclear fusion - Karyogamy of the two haploid nuclei = single diploid nucleus
3. Meiosis - 4 haploid cells
Sexual reproduction introduces genetic variation
Response to adverse environmental conditions
Two mating types are produced
Homothallic = both mating types present
Heterothallic = different but compatible mycelia required

Question 18

Key sexual structures of fungi

Answer 18

Basidiomycetes:
- Sterigma
- Basidium
- Basidiospore
- Immature basidia
Zygosporic fungi:
- Suspensors
- Zygospore
Chytrids:
- Antheridia
- Oospore
Asomycetes:
- Ascospores
- Ascus

Question 19

Basidiomycetes

Answer 19

Two types of reproductive structures
- Basidia – sexual
- Conidiophores – asexual (some species)
Clamp connection – hook-like structure ensures each cell/segment of hyphae receives a set of different nuclei
Genetic variation

Question 20

Asomycetes

Answer 20

Two types of reproductive structures
- Conidiophores – asexual
- Gametangia – sexual
Male gametangia
- Spermatium – detatched cell
- Antheridium – differentiated region
Female gametangia
- Ascogonium – always differentiated region

Question 22

Fungi importance in human life

Answer 22

Food
- Cheese, soy sauce, Quorn, fizzy drinks
Fermentation
- Beer, Wine, cider etc
Pharmaceuticals
- Antibiotics, cholesterol lowering drugs, immune suppressants
Washing powder
Biocontrol
Plant growth