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Microbiology - The Fungi

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    Study Guide Microbiolog y – The Fungi 1. Classification of Fungi 1.1 Division Zygomycota The division Zygomycota includes fungi known as zygomycetes . These fungi are commonly found as molds growing on bread, fruits, and other organic materials. A key feature of zygomycetes is that they can reproduce in two ways : • Sexually , by forming zygospores • Asexually , by forming sporangiospores

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    Study Guide Figure 1 Sexual reproduction in the mold Rhizopus stolonifer. Plus and minus mycelia produce sexually opposite hyphae that fuse and give rise to zygospores, which germinate to form new mycelia . 1.2 Sexual Reproduction in Zygomycetes During sexual reproduction, zygomycetes produce special spores called zygospores . These spores are thick - walled and help the fungus survive unfavorable conditions . Steps in Sexual Reproduction (Example: Rhizopus stolonifer ) 1. Two different mating types of mycelia, called plus (+) and minus ( – ) strains, grow close to each other. 2. Each mycelium produces special hyphae that grow toward one another.

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    Study Guide 3. These hyphae fuse together , a process known as hyphal fusion . 4. Fusion leads to the formation of a zygospore , which is a resistant sexual structure. 5. When conditions become favorable, the zygospore germinates . 6. It forms a sporangium , which releases spores. 7. These spores grow into new mycelia , completing the life cycle. 1.3 Asexual Reproduction in Zygomycetes In addition to sexual reproduction, zygomycetes also reproduce asexually by producing sporangiospores . • These spores are formed inside a structure called a sporangium • When released, sporangiospores germinate and grow into new fungal hyphae • This method allows rapid reproduction under favorable conditions Key Points to Remember • Zygomycota includes fungi called zygomycetes • They reproduce sexually (zygospores) and asexually (sporangiospores) • Zygospores are thick - walled and resistant • Rhizopus stolonifer is a common example used to study this process 2. Slime Molds Slime molds are unusual organisms because they show features of both molds (fungi - like) and protozoa (animal - like) . Their behavior changes depending on environmental conditions. 2.1 Amoeboid (Feeding) Stage – The Plasmodium Under favorable conditions, a slime mold exists as a soft, moving mass of cytoplasm . In this stage, it behaves much like an amoeba.

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    Study Guide • It moves slowly over rotting logs, leaves, and decaying organic matter • It feeds by phagocytosis , surrounding and engulfing food particles • This active feeding stage is called the plasmodium • The plasmodium is multinucleate , meaning it contains many nuclei within a single mass of cytoplasm 2.2 Formation of Fruiting Bodies The amoeboid stage ends when: • The plasmodium matures , or • The environment becomes harsh or unfavorable At this point: • The plasmodium moves toward a lighted area • It develops upright stalks called fruiting bodies • Spores are produced at the tips of these stalks These spores are highly resistant and can survive unfavorable environmental conditions. 2.3 Spore Germination and Life Cycle Continuation When conditions become suitable again: • The spores germinate • They form flagellated swarm cells or amoeboid cells • These cells eventually fuse together • Fusion results in the formation of a new multinucleate plasmodium This completes the slime mold life cycle.

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