BIOL121 intro to fungi

What are fungi?

Fungi are diverse eukaryotic organisms that can be unicellular (yeasts) or multicellular (molds/mushrooms)

What are the defining characteristics of fungi?

• Eukaryotic

• Cell walls made of chitin and polysaccharides

• Heterotrophic

• Reproduce sexually and asexually

• Usually haploid nuclei

Why are fungi considered heterotrophs?

They obtain energy by degrading complex organic molecules rather than photosynthesizing

Why can fungi not photosynthesize?

They contain no chlorophyll

What is a saprophyte?

A fungus that derives nutrients from dead organic matter

What is a necrophyte?

A fungus that kills organisms and then derives nutrients from them

What is a biotroph?

A fungus that derives nutrients from a living host.

Why are fungi considered successful heterotrophs?

They can use diverse carbon sources and occupy many ecological niches.

How are fungi different from plants?

• Fungi are heterotrophs; plants are autotrophs

• Fungi digest externally and absorb nutrients

• Fungi are filamentous

• Different cell wall composition

• Fungal mitosis occurs within the nucleus

What is the major component of fungal cell walls?

Chitin

Which organisms are the closest relatives of fungi?

Animals

What are yeasts?

Single-celled fungi that reproduce mainly by budding

What is budding in yeasts?

Asexual reproduction where a daughter cell forms from the parent cell

What are hyphae?

Long thread-like filaments that make up fungal bodies

What is a mycelium?

A mass or network of hyphae

What is polarized tip growth?

Growth occurring mainly at the tips of hyphae

What are dimorphic fungi?

Fungi that can switch between yeast and filamentous forms depending on environmental conditions

What environmental cues can trigger dimorphism?

Temperature and CO₂ levels

Why are fungal spores important?

They allow reproduction, dispersal, and survival

How do filamentous fungi reproduce asexually?

By producing lightweight haploid spores

When does sexual reproduction usually occur in fungi?

When nutrients are scarce.

What is the purpose of sexual spores?

They are hardy structures that help fungi survive adverse conditions

What is heterothallism?

Sexual reproduction requiring two compatible mating types

What is homothallism?

The ability of some fungi to self-fertilize.

What are the three major fungal phyla discussed?

• Zygomycota

• Ascomycota

• Basidiomycota

What are the characteristics of Zygomycetes?

• Aseptate hyphae

• Produce sporangiospores asexually

• Produce zygospores sexually

• Mostly saprophytes

What is an example of a zygomycete?

Rhizopus stolonifer (bread mold)

What are sporangiospores?

Asexual spores produced inside sporangia

What is a zygospore?

A diploid sexual spore formed in zygomycetes

What are the characteristics of Ascomycetes?

• Septate hyphae

• Produce conidiospores asexually

• Produce ascospores sexually

What are conidiospores?

Asexual spores formed on conidiophores

What are ascospores?

Sexual spores produced in asci after meiosis

Name important ascomycete model organisms

• Saccharomyces cerevisiae

• Aspergillus nidulans

• Neurospora crassa

What are the characteristics of Basidiomycetes?

• Septate hyphae

• Produce basidiospores sexually

• Often form basidiocarps (fruiting bodies)

What are basidiospores?

Sexual spores produced after meiosis in basidiomycetes.

What is a basidiocarp?

The fruiting body of a basidiomycete, such as a mushroom

What ecological role do many basidiomycetes play?

They decompose lignin in wood

What is an edible basidiomycete example?

Agaricus bisporus

What are rust fungi?

Plant pathogens belonging to the basidiomycetes

What are Deuteromycetes?

“Fungi imperfecti” with no known sexual reproduction cycle

Why were Deuteromycetes called fungi imperfecti?

Because only their asexual stage was known

What are examples of important Deuteromycetes?

• Aspergillus flavus

• Aspergillus niger

What is the difference between septate and aseptate hyphae?

• Septate hyphae have cross walls

• Aseptate hyphae lack cross walls

What is the ploidy of most fungal hyphae?

Haploid

Why are fungi ecologically important?

They decompose organic matter, recycle nutrients, form symbioses, and act as pathogens