Chapter 31

Fungi

General characteristics of Fungi• General characteristics:

• eukaryotic• mostly multicellular; some unicellular• cell walls made of chitin (animal feature)• usually filamentous bodies (filaments called hyphae)• external heterotrophs; principal decomposers• exhibit nuclear mitosis• reproduce sexually or asexually

• Examples:• Amanita muscaria - mushroom (p. 604)• Penicillium and Aspergillus (p. 613)• Rhizopus stolonifer (black bread mold) (p. 609)• yeasts ex: Saccharomyces cerevisiae (p. 611)

Candida - cause of thrush• pathogens that cause athlete’s foot and ringworm• Treatment of fungal diseases is difficult because of their similarity

to animals

Structure:hyphae - the filaments of a fungusmycelium - tangled mass of hyphae *** large surface area, therefore good

absorption of food

septa - dividing walls in a hyphaNutrition: All fungi digest food outside their bodies (external digestion).

*** Important decomposers*** Can compete for our food

Structure and function of hyphae

Mitosis divides nucleus and not hyphae• Some hyphae have one nucleus –

monokaryotic

• Some hyphae have two nuclei – dikaryotic

• During Mitosis, nuclear envelope does not break and reform.

• Spindle apparatus is formed within the nucleus by spindle plaques (centrioles are absent)

• Secrete digestive enzymes and absorb organic molecules – external digestion

Fig. 31.6

Five main groups of Fungi

Deuteromycetes-Imperfect fungi lack phylogenetic position, no sexual reproduction and less data to support its relation to fungi

Various groups of Fungi

• Chytridiomycetes are closely related to ancestors of early fungi

• Aquatic fungi with flagellated zoospores• Glomeromycetes (asexual plant symbionts)

form intracellular associations with plant roots called arbuscular mycorrhizae.

• No sexual reproduction• Possible role in evolution of terrestrial plants

Meiosis (sexual)– Zygosprangium forming zoospores

Mitosis (asexual) – sporangiophores form sporangia

Zygomyetes: produce zygotes, example Rhizopus – (grows on bread)

Ascomycetes: The Sac (ascus) fungi

• Members are bread yeasts, common molds, morels, cup fungi and truffles.

• Plant pathogens are Cryphonectria parasitica – chestnut blight

• Ophiostoma ulmi – Dutch elm disease• Penicillium and Aspergillus genera

(Deuteromycetes)• Candida milleri – sourdough bread• Saccharomyces cerevisiae- wine preparation

Meiosis – Ascocarp forming four haploid daughter nuclei

Mitosis-Ascospores with eight daughter nuclei that release conidia

Basidiomycetes: The club (Basidium) Fungi

• Members include Mushrooms, toadstools, puffballs, jelly fungi, and shelf fungi

• Pathogens – Rusts and smuts

• Some mushrooms can be deadly poisonous

Meiosis results in basidium - basidiopsores

Range of Symbioses

• Obligate Symbiosis – essential for survival• Facultative Symbiosis – the fungus can survive

without host• Parasites and Pathogens gain resources from host

and kill it• Commensal – one partner is benefited but neither is

harmed• Mutualistic relationship – both are benefited• Endophytic fungi live inside plants and protect them

from parasites

Mycorrhizae

• Mycorrhizae are fungi associated with roots of plants• Fungi aid in transfer of P, Zn, Cu and other mineral

nutrients from soil into roots• Plant provides organic carbon to fungus • Arbuscular Mycorrhizae- the hyphae penetrates

into the roots and into the surroundings of the plant• Ectomycorrhizae – the hyphae do not penetrate the

root and only surround it

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