Biology 106 Lecture Topic # 20: Diversity- Fungi
I. Fungal Diversity
A. So DISTINCT placed in own Kingdom
B. Characteristics of Fungi
C. Generalized Structure: -- vegetative bodies of most fungi are hidden, diffusely organized around, w/in tissues of food , -- basic building units are hyphae = minute threads composed of tubular walls surrounding their plasma membranes and cytoplasm, -- hyphae are arranged as a network known as mycelium, -- hyphae divided into cells by cross walls called septa, -- septa have pores lg. enough to allow ribisomes, mito., and nuclei flow freely from cell to cell-- septa built of chitin.
D. Growth and Reproduction
1. Fungal mycelium grow rapidly, conc. on length not girth, exploration
- reproduce via spores, formed sexually & asexually
- spores usually unicellular and formed in specialized cells of the hyphae
- sex usually triggered by change in environment, i.e., food depletion
- nuclei of hyphae & spores haploid, - diploid stage transient, only formed during sexual reproduction, - hyphae can contain nuclei from diff. individuals due to hyphal fusion.
2. Sexual Cycle - hyphae of different mating strains fuse = plasmogamy nuclei from different hyphae pair up, but do NOT fuse = dikaryon (can exist for months,years)
- some adv's of diploidy, i.e., genes in one nucleus can compensate for genes in the other
- finally, the nuclei fuse to form diploid cell , meiosis immed. -> genetically diverse spores!
E. Classification of Fungi (100 k)
1. Divided into 3 major groups w/r to sexual life history:
a. Zygomycota: - 600 species, - mostly terrestrial, - coenocytic hyphae
- repro. hyphae fuse, nuclei pair off , - cells develop rough, thick walled coating, resists drying & harsh envir's, - form zygosporangia, - karyogamy = and occurs under favorable conditions followed by meiosis, - zygosporangium -> germinates-> sporangium -> disperses spores
ex.'s -
b. Ascomycota: >60, 000 species, - defining feature is a saclike Asci where sexual spores are produced. Borne in macroscopic fruiting body = Ascocarp, - dikaryotic stage is more extensive than zygomycetes, ex.'s
c. Basidiomycota: >25,000 species, - defining feature is fruiting body that produces sexual spores = Basidiocarp, - after plasmogamy, dikaryotic mycelium is very long-lived, - In response to envir. cue mycelium reproduce via Basidiocarp, ex. mushroom, - basidiocarp may produce millions of spores, ex.'s
F. Lifestyles of the Rich and Fungal: Certain morphological and ecological specializations have evolved independently in the 3 divisions of fungi.
1. Molds: - grow rapidly, - asexually repro. fungus, - mycelium grow as saprobes or parasites on substrates, - called Imperfect Fungi or Deuteuromycota ex.'s
2. Yeasts: - unicellular fungi, - 2nd evolved from multicellular forms, - inhabit liquid, or moist habitat, repro. asex. by simple cell division, or pinching off of bud cells, ex.'s
3. Lichens: - Association betw. fungal hyphae & algae, > 25,000 species, Fungal Component usually asco., but several basidio.also known, -lichen shape, structure, mass- provides physical environment, pigments to shade from sun, secretes acid to breakdown substrate & absorb minerals. Algal Component is a filamentous green algae or cyanobacteria, - housed in an inner layer below lichen surface, - provides food, fix nitrogen if a cynaobacteria, Ongoing controversy whether association is symbiotic or parasitic, ex.'s 4. Mycorrhizae: - fungus roots, > 95% plant species , - all 3 divisions represented, - ectomycorrhizae = , - endomycorrhizae = .
G. Evolution of Fungi - unclear, probable ancestor protista, invaded land with plants.