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Chapter 18Fungus
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18.1 Fungi are adapted for nutrition by absorption
hyphae: tiny threads of cytoplasm surrounded by a plasma membrane and covered by a cell wallCell walls made of chitin– Strong , flexible
polysaccharide
Cross-walls: divide the long filaments into many cells – Exchange cytoplasm,
organelles and distribute nutrients
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Mycelium
mycelium(mycelia): interwoven mat of hyphae–Feeding structure–Maximizes surface area within food–Km of hyphae each day– In Oregon, mycelium is 5.5 km
across, 9 km2 of forest, 2400 years old
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Nutrition
absorptive nutrition: method by which the fungus absorbs small organic molecules from its surroundings– Digests food outside mycelium by secreting
enzymes– Enzymes break down molecules so they can be
absorbed
Food sources– Fallen logs, dead animals, waste– Parasitic fungi: absorb nutrients from living hosts
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Reproduction
spores: haploid single cells with thick cell walls – Spread by wind and can withstand unfavorable
conditions– Most are asexual– Sexual reproduction: haploid hyphae from
different mycelia fuse together and combine genetic info
Can produce trillions of spores– Puffballs– Found 200 km above the surface
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18.2 Kingdom Fungi consists of diverse forms
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Zygote Fungi Mostly terrestrial and live in soil or decaying materialRhizopus stolonifer Food available= asexual reprod.– Sporangia: spore-forming structures at tips of hyphae
Food depleted= sexual– Two mycelia fuse– zygosporangium: reproductive structure
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Sac Fungi
Marine, freshwater, and terrestrial
Single-celled or large morels
Ascus (sac) contains spores
Similar reproduction to zygote fungus
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Club Fungi
Agaricus bisporus – Most common
Important decomposers of wood and plant material– Some are parasites
Usually sexual– Spores drop from
“gills” underneath– Can grow within hours
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Club Fungi Reproduction
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YeastSingle-celled fungiInhabit liquid or moist habitats– Plant sap and animal tissues
Reproduce asexually – Cell division or pinching of “buds”
Some sexually – Form ascus or basidium; classified as sac or club– Imperfect fungi: no known sexual stage of
reproduction
Used for fermentation or raise dough
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MoldAny fungus that grows very rapidly on a surface
Most asexual
Some imperfect
Sexual stages place some in zygote, sac, or club
Rhizopus - zygote
Penicillium - sac
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Mmmmm…. cheesy
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18.3 Fungi have a major impact on other life.
Symbiotic fungi– Close relationship between two different
species that benefits at least one of them– Mutualistic: both benefit
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Lichen
lichen: mutualistic pairing of a fungus and an alga– Photosynthetic algae feed
the fungus– Fungal mycelium provides a
good habitat
Usually a sac fungus and either green algae or cyanobacteriaMore than 25,000 “species” of lichen
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Benefits of lichen symbiosis
Environments where neither could live on its own
Pioneer organisms
Tundra
Do not tolerate air pollution; death of lichen = poor air quality
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Mycorrhizae
Symbiotic relationship between fungal hyphae and plant roots
Fungus provides
more water and nutrients, plant provides sugar
Mushrooms
around trees
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Disease-causing fungi
30% of fungi are parasitic
Dutch Elm disease– Eliminated most elm
trees in N Amer
50 species parasitic in humans and other animals– Yeast infections
– Ringworm• Athlete’s Foot
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Commercial Uses Truffles
Cheese– Fungi “ripen” them
Yeast for baking and brewing
Antibiotics
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Chemical Cycling
Decompose matter
Circulate carbon and nitrogen
Some can decompose clothing, boots, glue, and plastic