Fascinating World of Fungi: Characteristics and Importance in Ecosystems

1. Chapter 31 Reading Quiz • What are the filaments called that make up mycelium? • What are fungi cell walls made of? • What characteristic does “dikaryotic” refer to? • The symbiotic relationship between a green alga & a fungus is called… • About what % of the 100,000 fungus species are parasitic?

2. 1. List characteristics that distinguish fungi from organisms in other kingdoms. • Fungi are very different • They differ in: 1. Nutrition 2. Structural organization 3. Growth and reproduction 

3. 2. Explain how fungi acquire their nutrients. • They secrete hydrolytic enzymes and acids to decompose complex molecules into simpler ones that can be absorbed • Saprobes • Parasites • Mutualistic fungi 

4. 3. Explain how non-motile fungi seek new food sources and how they disperse. • Through extensions of hyphae that can grow up to a kilometer total per day • Parasitic fungi have “haustoria” which penetrate a host for nutrition 

6. 4. Describe the basic body plan of a fungus. • Hyphae  make up the mycelium (the underground part of the fungus) • Composed of “chitin” (a nitrogen-containing polysaccharide) • Hyphae provide a large surface area with which to increase absorption 

7. Septate  Divided into cells by crosswalls called septa – pores allow organelles to move around Aseptate  Hyphae lack crosswalls and are coenocytic (formed form repeated nuclear division without cytokinesis)  5. Distinguish between septate and aseptate (coenocytic) fungi.

9. Terms to know… Syngamy  sexual union of haploid cells (2 phases) • Plasmogamy  the fusion of cytoplasm • Karyogamy  the fusion of nuclei

11. 6. Describe some advantages to the dikaryotic state. • After plasmogamy, haploid nuclei from each parent pair up forming a dikaryon, but they do not fuse • Nuclear pairs in dikaryons may exist and divide synchronously for months or years • Advantages  one haploid genome may compensate for harmful mutations in the other nucleus 

12. 7. Distinguish among fungi and list some common examples of each. • Chytridiomycota  chytrids • Zygomycota  mycorrhizae, Rhizopus • Ascomycota  yeasts, cup fungi, septate hyphae • Basidiomycota  club fungi, mushrooms, shelf fungi, puffballs 

14. 8. Describe asexual and sexual reproduction in Zygomycota, Ascomycota, and Basidiomycota, and the sexual structure that characterizes each group. Zygomycota  zygote fungi form resistant dikaryotic structures during sexual reproduction (sporangia) Ascomycota  asexual: form conidia, sexual: form ascospores in an ascus Basidiomycota  asexual: not common and result in conidia, sexual: form basidiocarps 

16. 9. Explain the difference between conidia and ascospores. Ascomycota  • Conidia – tips of specialized hyphae, haploid, spores for wind dispersal (asexual) • Ascospores – haploid mycelia of opposite mating strains fuse and develop spores within an ascus (sexual) 

18. Zygomycota, Ascomycota, Basidiomycota, Chytridiomycota

19. 10. Explain why ascomycetes can be useful to geneticists studying genetic recombination. • They are found in marine, freshwater, and terrestrial habitats • Plasmogamy gives rise to dikaryotic hyphae and the tips become asci • Karyogamy combines the parental genomes and meiosis forms genetically varied ascospores • In many asci, 8 ascospores are lined up in a row in the order in which they formed from zygote • This arrangement provides geneticists with an opportunity to study genetic recombination – differences reflect crossing over and independent assortment of chromosomes during meiosis 

20. 11. Explain why the Deuteromycota are called imperfect fungi. • These are the molds with no known sexual stages • Reproduce asexually by producing spores • Provide a source for antibiotics for humans 

21. 12. Describe the anatomy of lichens and explain how they reproduce. • These are highly integrated symbiotic associations of algal cells (usually filamentous green algae or cyanobacteria) with fungal hyphae (usually ascomycetes) • Alga is located below the lichen’s surface and provides food for fungus and may fix nitrogen • Fungus provides suitable environment and protection for algae and absorbs minerals, water 

23. 13. Provide evidence for both sides of the debate on whether symbiosis in lichens is parasitic or mutualistic. • Mutualism – fungi benefit the algae and lichens can survive in habitats that are inhospitable to either organism alone • “controlled” parasitism – fungi actually kills some algal cells, though not as fast as algae replenishes itself 

24. 14. Describe the ecological importance of lichens. • They are important pioneers – break down rocks and allow colonization by other plants • Can tolerate severe cold • Photosynthesis occurs when lichen water content is 65 – 75% • Lichens are sensitive to air pollution due to mode of mineral uptake – provide a good idea of how polluted an area is 

25. 15. Explain why fungi are ecologically and commercially important. • Fungi and bacteria are the principal decomposers on earth • Fungi also are pathogens  athlete’s foot, ringworm, yeast infections, plant infections • 10 – 50% of the world’s fruit harvest is lost yearly due to fungal infections 

28. 16. Describe how the mutualistic relationship in mycorrhizae is beneficial to both the fungus and the plant, and explain its importance to natural ecosystems and agriculture. • Mycorrhizae  specific mutualistic associations of plant roots and fungus • Fungi increases the absorptive surface of roots and exchanges soil minerals • mycorrhizae are seen in 95% of all vascular plants; they are necessary for optimal plant growth and function 

30. 17. Describe a scenario for fungal phylogeny and list two possible ancestors of Zygomycota. • Fungi and animals probably evolved from a common protist ancestor • Molecular evidence supports that the four fungal divisions are monophyletic (flagellated cells, etc) • Flagella are lost in the chytrid lineage to Zygomycota 