Lecture 7: Fungi
1. Absorptive
nutrition enables fungi to live as decomposers and symbionts
2. Extensive
surface area and rapid growth adapt fungi for absorptive nutrition
3. Fungi disperse
and reproduce by releasing spores that are produced either sexually or
asexually
4. Many fungi have
a heterokaryotic stage
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Ecosystems would be in trouble without fungi to
decompose dead organisms, fallen leaves, feces, and other organic materials.
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This decomposition recycles vital chemical
elements back to the environment in forms other organisms can assimilate.
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Most plants depend on mutualistic fungi that
help their roots absorb minerals and water from the soil.
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Human have cultivated fungi for centuries for
food, to produce antibiotics and other drugs, to make bread rise, and to
ferment beer and wine.
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Fungi are eukaryotes and most are multicellular.
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While once grouped with plants, fungi generally
differ from other eukaryotes in nutritional mode, structural organization,
growth, and reproduction.
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Molecular studies indicate that animals, not
plants, are the closest relatives of fungi.
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Fungi are heterotrophs
that acquire their nutrients by absorption.
•
They absorb small organic molecules from the
surrounding medium.
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Exoenzymes,
powerful hydrolytic enzymes secreted by the fungus, digest food outside its
body to simpler compounds that the fungus can absorb and use.
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The absorptive mode of nutrition is associated
with the ecological roles of fungi as decomposers (saprobes), parasites, or
mutualistic symbionts.
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Saprobic fungi absorb
nutrients from nonliving organisms.
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Parasitic fungi absorb nutrients from the cells
of living hosts.
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Some parasitic fungi, including some that infect
humans and plants, are pathogenic.
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Mutualistic fungi also absorb nutrients from a
host organism, but they reciprocate with functions that benefit their partner
in some way.
5. Fungi colonized
land with plants
6. Fungi and
animals evolved from a common protistan ancestor
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The fossil record indicates that terrestrial
communities have always been dependent on fungi as decomposers and symbionts.
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The oldest undisputed fossil fungi date back 460
million years, about the time plants began to colonize
land.
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Fossils of the first vascular plants from the
late Silurian period have petrified mycorrhizae.
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Plants probably moved onto land in the company
of fungi.
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Molecular evidence supports the widely held view
that the four fungal divisions are monophyletic.
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The occurrence of flagella in chytrids, the oldest fungal lineage, indicates that fungal
ancestors were aquatic flagellated organisms.
•
Flagellated cells were lost as ancestral fungi
became increasingly adapted to life on land.
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Many of the differences among the Zygomycota, Ascomycota, and Basidiomycota are different solutions to the problem of
reproducing and dispersing on land.