Chapter Summary

• Fungi are distinguished from other opisthokonts by absorptive heterotrophy and by the presence of chitin in their cell walls. Review Figure 29.1

• Some fungi are saprobes, others are parasites or predators, and some are mutualists.

• Yeasts are unicellular, free-living fungi.

• The body of a multicellular fungus is a mycelium—a meshwork of filaments called hyphae. Hyphae may be septate (having septa) or coenocytic (multinucleate). Review Figure 29.3

• Saprobic fungi, which act as decomposers, make crucial contributions to the recycling of elements, especially carbon.

• Many fungi are parasites, harvesting nutrients from host cells by means of haustoria. Review Figure 29.5

• Certain fungi have relationships with other organisms that are symbiotic and mutualistic.

• Some fungi associate with unicellular green algae, cyanobacteria, or both to form lichens, which live on exposed surfaces of rocks, trees, and soil. Review Figure 29.8

• Mycorrhizae are mutualistic associations of fungi with plant roots. They improve a plant’s ability to take up nutrients and water.

• Endophytic fungi live within plants and may provide their hosts with protection from herbivores and pathogens.

• The microsporidia, chytrids, and zygospore fungi diversified early in fungal evolution. The arbuscular mycorrhizal fungi, sac fungi, and club fungi form a monophyletic group, and the latter two groups form the clade Dikarya. Review Figure 29.11, Table 29.1, Activity 29.1

• Many species of fungi reproduce both sexually and asexually. In many fungi, sexual reproduction occurs between individuals of different mating types. Review Figure 29.12

• The microsporidia are highly reduced unicellular fungi. They are obligate intracellular parasites of animals.

• The three distinct lineages of chytrids all include species with flagellated gametes. Review Figure 29.15A

• In the sexual reproduction of terrestrial fungi, plasmogamy (fusion of cytoplasm) precedes karyogamy (fusion of nuclei).

• Zygospore fungi have a resting stage known as a zygospore, which contains many diploid nuclei. Their spores are dispersed from simple stalked sporangiophores. Review Figure 29.15B, Animation 29.1

• Arbuscular mycorrhizal fungi form symbiotic associations with plant roots. They are only known to reproduce asexually. Their hyphae are coenocytic.

• In sac fungi and club fungi, a mycelium containing two genetically different haploid nuclei, called a dikaryon, is formed. The dikaryotic (n + n) condition is unique to the fungi. Review Figure 29.17, Activity 29.2

• Sac fungi have septate hyphae with large pores; their sexual reproductive structures are asci. Some sac fungi are unicellular yeasts. Many filamentous sac fungi produce fleshy fruiting structures called ascomata. The dikaryon stage in the sac fungus life cycle is relatively brief. Review Figure 29.17A

• Club fungi have septate hyphae with distinctive small pores. Their fruiting structures are called basidiomata, and their sexual reproductive structures are basidia. The dikaryon stage may last for years. Review Figure 29.17B

• Some fungi are consumed as food by humans; other fungi are critical in baking, fermentation, and flavoring food.

• Fungi play important roles in cleaning up environmental pollutants such as synthetic petroleum-derived hydrocarbons.

• The diversity and abundance of lichen growth on trees is a sensitive indicator of air quality.

• Reforestation projects require restoration of the mycorrhizal fungal community.

• Several species of fungi are important model organisms.

• Fungi provide important weapons against diseases and pests.