AP Biology Chapter 31
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What are characteristics that distinguish fungi from organisms in other kingdoms?
- structural organization
- growth and reproduction
How do fungi acquire their nutrients?
- Fungi secrete hydrolytic enzymes and acids to decompose complex molecules into simpler ones that can be absorbed.
- Saprobes (decomposers)
- Mutualistic fungi
How do non-motile fungi seek new food sources and how do 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.
What is the basic body plan of a fungus?
- They have hyphae that make up the mycelium (the underground part of the fungus).
- They are composed of “chitin” (a nitrogen-containing polysaccharide).
- Hyphae provide a large surface area with which to increase absorption.
What is the difference between septate and aseptate (coenocytic) fungi?
- Septate fungi are divided into cells by crosswalls called septa – pores allow organelles to move around.
- In aseptate fungi, hyphae lack crosswalls and are coenocytic (formed form repeated nuclear division without cytokinesis).
What is syngamy?
- Syngamy is the sexual union of haploid cells (2 phases)
- 1.Plasmogamy (the fusion of cytoplasm)
- 2.Karyogamy (the fusion of nuclei)
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.
- One haploid genome may compensate for harmful mutations in the other nucleus.
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
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
Explain the difference between conidia and ascospores.
- 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)
Explain why ascomycetes can be useful to geneticists studying genetic recombination.
- They are found in marine, freshwater, and terrestrial habitats.
- 1.Plasmogamy gives rise to dikaryotic hyphae and the tips become asci.
- 2.Karyogamy combines the parental genomes and meiosis forms genetically varied ascospores.
- 3.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.
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
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
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
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
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
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
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
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