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The Major Groups of Fungi Help (page 2)

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By — McGraw-Hill Professional
Updated on Aug 30, 2011

Phylum Zygomycetes (the Zygote Fungi)

A third group of fungi are those of the Phylum Zygomycetes ( zeye -go-my- SEE -teez), literally the “yoked together” ( zygo -) “fungi.” This phylum of fungi derives its name from the inclusion of a zygote ( ZEYE -goat) within its life cycle. A zygote consists of two sex cells, called gametes ( GAM -eats), that are literally fused, yoked, or “married” ( gamet ) together during fertilization.

The so-called zygote fungi in this group utilize sexual reproduction – the fusion of two gametes together to create a zygote. Once formed, the zygote then divides repeatedly by the process of mitosis (Chapter 5), thereby creating a new adult organism. The zygotes are enclosed in thick-walled zygospores ( ZEYE -go-spoors), which are shed and sent wafting out through the air to new locations.

A typical zygomycetic ( zeye -go-my- SEE -tick) fungus is the black bread mold, genus Rhizopus ( RYE -zuh-pus) – “root” ( rhiz ) “feet” ( pus ). Interestingly enough, like many fungi, the Rhizopus group can engage in both sexual reproduction (gametes uniting to form zygotes), as well as asexual ( AY - sex -you-al) reproduction that occurs “without” ( a -) gametes. For simplicity, just the asexual reproduction of the black bread mold is displayed in Figure 8.4.

A spore lands on a piece of white bread, then begins to germinate ( JER -muh- nayt ). The landed spore “sprouts” a number of slender, thread-like hyphae, which soon merge to form a white, extensively branching mycelium, deep inside the bread slice. Soon, a large number of round-topped sporangia (spoh- RAN -jee-ah) or “seed” (spor) “vessels” (angi), appear like tiny black puffballs. The round, black sporangia are attached to the bread surface by long, narrow stalks. The mold is called Rhizopoda, because the sporangia and their stalks are firmly anchored into the bread surface by means of rhizoids ( RYE -zoyds) – blunt, “root-resembling” or “foot-resembling” projections. When the wind blows, masses of black spores are scattered from the rounded sporangia, which hold thousands of them. A spore may land on another piece of bread, and the life cycle of the mold begins anew.

The Fungi: Not Just Mushrooms! The Major Groups of Fungi Phylum Zygomycetes (the Zygote Fungi)

Fig. 8.4 The asexual life cycle of Rhizopus or black bread mold.

Phylum Chytridiomycetes and Fungi Summary

Phylum Chytridiomycetes (water-dwelling Fungi)

A fourth phylum of fungi is the Phylum Chytridiomycetes ( KIH -trid-e-oh-my- SEE -teez) or “water-dwelling” (chytrid) “fungi.” The members of this group with an extremely tongue-twisting name are more easily called chytrids ( KIT -rids), because they are mainly “water-dwellers.”

Recent evidence suggests that the chytrids are the most primitive fungi, and that they were the first type to evolve from protists having flagella. Dwelling in an aqueous (watery) environment, each chytrid has a small, globe-shaped body. It produces a highly active spore which has a flagellum attached. In their adult stage, the chytrids make a large mycelium (network) consisting of an extensive tangle of slender hyphae. These highly branched hyphae create a large area for the easy absorption of nutrients dissolved in the surrounding water.

Summary Diagram of the Fungi

Figure 8.5 provides summary pictures and brief descriptions of each of the four major phyla of fungi we have been studying.

The Fungi: Not Just Mushrooms! The Major Groups of Fungi Phylum Chytridiomycetes (water-dwelling Fungi)

Fig. 8.5 A summary of the four major phyla of fungi.

 

Practice problems for these concepts can be found at:  The Fungi: Not Just Mushrooms Test

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