Fungi

1. Fungi Chapter 31 By: Katie Quinlan

2. Absorptive nutrition enables fungi to live as decomposers and symbionts • Fungi are heterotrophs that acquire their nutrients by absorption. • Small organic molecules are absorbed from the surrounding medium • Fungus digests food outside its body by secreting powerful hydrolytic enzymes into the food • Enzymes decompose complex molecules to the simpler compounds that the fungus can absorb and use • Three types of fungi: • Saprobic fungi: absorb nutrients from nonliving organic material • Parasitic fungi: absorb nutrients from the cells of living hosts • Mutualistic fungi: absorb nutrients from a host organism, but they reciprocate with functions beneficial to their partners • Most common in terrestrial habitats; some inhabit aquatic environment.

3. Extensive surface area and rapid growth adapt fungi for absorptive nutrition • The bodies of fungi are constructed of units called hyphae • Hyphae are minute threads composed of tubular walls surrounding plasma membranes and cytoplasm. • Hyphae form a interwoven mat called a mycelium (the “feeding” network of a fungus • Most fungi are multicellular with hyphae divided into cells by cross-walls, or septa. • Generally have large pores large enough to allow ribosomes, mitochondris, and nuclei to flow from cell to cell • Most build their cell walls of chitin (strong but flexible nitrogen-containing polysaccharide) • Some fungi are aseptate (hyphae are not divided into cells by cross-walls) • Known as coenocytic (consist of continuous cytoplasmic mass with hundreds or thousands of nuclei) • Parasitic fungi usually have some of their hyphae modified as haustoria (nutrient-absorbing hyphal tips that penetrate the tissues of the host)

4. Characteristics of fungal hyphae

5. Fungi reproduce by releasing spores that are produced either sexually or asexually

6. Chytrids may provide clues about fungal origins • Chytrids may be a link between fungi and protists • Mainly aquatic • Some are saprobes, others parasitize protists, plants, and aquatic invertebrates • They are an absorptive mode of nutrition and cell walls made of chitin • Form coenocytic hyphae, although some are unicellular • Have some key enzymes and metabolic pathways that are common among fungi • Most primitive fungi ( they belong to the lineage that diverged earliest in the phylogeny of fungi)

7. Phylogeny of fungi

8. Zygomycota • These fungi are mostly terrestrial and live in soil or on decaying plant and animal material • One group or major importance forms mycorrhizae (mutualistic associations with the roots of plants) • Zygomycete hyphae are coenocytic, with septa found only where reproductive cells are formed. • Common zygonycete is black bread mold

9. Life cycle of black bread mold

10. Ascomycota: Sac fungi produce sexual spores in saclike asci • Ascomycetes, or sac fungi, have been described from a wide vafriety of marine, freshwater, and terrestrial habitats. • Range in size and complexity • Include some of the most devastating plant pathogens • Many are important saprobes (particularly of plant material) • Half live with algae in symbiotic associations called lichens • Some form mycorrhizae with plants • Others live in leaves on the surface of mesophyll cells, where the fungi apparently help protect these plant tissues from insects by releasing toxic compounds.

11. Life cycle of an ascomycete

12. Basidiomycota: Club fungi have long-lived dikaryotic mycelia and a transient diploid stage • Name derives from the basidium, a transient diploid stage in the organism’s life cycle • Clublike shape of the basidium also gives rise to the common name club fungus. • Improtant decomposers of wood and other plant material. • Division includes mycorrhiza-forming mutualists and plant parasites • Best at decomposing the complex polymer lignin, an abundant component of wood • Two groups: • Rusts • Smuts • Reproduces sexually by producing elaborate friuting bodies called basidiocarps • An example is a mushroom

13. Yeasts • Yeasts are unicellular fungi that inhabit liquid or moist habitats. • Reproduce asexually, by simple cell division or by pinching of small “bud cells” off a parent cell. • Some reproduce sexually, by forming asci or basidia (classified as Ascomycota or Basidiomycota)

14. Lichens

15. Molds • A rapidly growing, asexually reproducing fungus • Mycelia of these fungi grow as saprobes or parasites on a great variety of substrates. • Mold produces asexual spores • Same fungi may reproduce, producing zygosporangia, ascocarps, or basidiocarps. • Molds can be classified as zygomycetes, ascomycetes, or basidiomycetes because of known sexual stages. • Those are collectively called deuteromycetes (imperfect fungi). • These reproduce asexually by producing spores. • Penicillium (fermenters)