Classification and importance of fungi

Biology · Kingdom Fungi. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Fungi are placed in four groups according to the structure that bears their sexual spores. Zygomycota form thick-walled zygospores. Ascomycota (sac fungi) form ascospores inside a sac called an ascus. Basidiomycota (club fungi) form basidiospores on the outside of a club-shaped basidium. Deuteromycota (imperfect fungi) are those in which no sexual stage has been seen.

Fungi matter in three ways. In nature they are decomposers and partners in lichens and mycorrhizae. For people they give food, drugs and industrial products. They also spoil food and cause disease in crops and humans.

Rules to remember

Zygomycota: non-septate hyphae, zygospores; Rhizopus (black bread mould).
Ascomycota: usually 8 ascospores in each ascus; yeasts, morels, truffles, powdery mildews.
Basidiomycota: 4 basidiospores on each basidium; mushrooms, puffballs, rusts and smuts.
Deuteromycota: reproduce by conidia only; Penicillium, Aspergillus.
Yeast (Saccharomyces cerevisiae) ferments sugar: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. The carbon dioxide raises bread dough.
Useful products: penicillin from Penicillium, cyclosporine for organ transplants. Harmful: aflatoxins from Aspergillus flavus; ergotism from Claviceps purpurea on rye.
Diseases: rusts (Puccinia) and smuts (Ustilago) in wheat; ringworm and athlete's foot of the skin; candidiasis caused by Candida.

Common mistake

Students mix up the spore numbers and positions. Ascospores are inside the ascus, usually 8; basidiospores are outside on the basidium, usually 4.

Worked example

A blue-green mould grows on an orange. Its hyphae are septate and it forms chains of conidia on brush-like conidiophores. No sexual stage has ever been found. Which group is it placed in, and which fungus is it likely to be?

Septate hyphae rule out Zygomycota, which have non-septate hyphae.
Classification needs the sexual structure (ascus or basidium); here none is known.
Fungi with no known sexual stage that reproduce by conidia are placed in Deuteromycota.

Answer: Deuteromycota (imperfect fungi); the brush-like conidiophores suggest Penicillium.

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Chapter 8: Kingdom Fungi

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