fungi – fungi recycle vital chemical elements back to the environment in forms other organisms can...
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FUNGI
– Fungi• Recycle vital chemical elements back to the environment
in forms other organisms can assimilate • Form mycorrhizae, fungus-root associations that help
plants absorb from the soil– Minerals – Water
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– Fungi are• Eukaryotes • Typically multicellular• More closely related to animals than plants, arising from a
common ancestor about 1.5 billion years ago
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Orange fungi
Mold
Predatory fungus
Budding yeastA “fairy ring”
Bud
Roundworm Body of fungus
Colo
rized
SEM
Colo
rized
SEM
Colo
rized
SEM
Figure 16.22
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– A fungus• Digests food outside its body (extracellularly)• Secretes powerful digestive enzymes to break down the food• Absorbs the simpler food compounds
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Fungal Structure– The bodies of most fungi are constructed of threadlike filaments
called hyphae.– Hyphae are minute threads of cytoplasm surrounded by a
• Plasma membrane • Cell wall mainly composed of chitin
– Hyphae branch repeatedly, forming an interwoven network called a mycelium (plural, mycelia), the feeding structure of the fungus.
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Reproductivestructure
MyceliumMycelium
Hyphae Spore-producingstructures
Figure 16.23
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Fungal Reproduction
– Mushrooms• Arise from an underground mycelium • Mainly function in reproduction
– Fungi reproduce by releasing billions and trillions of spores that are produced either sexually or asexually.
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Fungi as Decomposers
– Fungi and bacteria• Are the principal decomposers of ecosystems • Keep ecosystems stocked with the inorganic nutrients necessary
for plant growth
– Without decomposers, carbon, nitrogen, and other elements would accumulate in nonliving organic matter.
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Parasitic Fungi
– Parasitic fungi absorb nutrients from the cells or body fluids of living hosts.
– Of the 100,000 known species of fungi, about 30% make their living as parasites, including• Dutch elm disease • Deadly ergot, which infests grain
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(a) American elm trees killed by Dutchelm disease fungus
Figure 16.24a
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(b) ErgotsFigure 16.24b
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– About 50 species of fungi are known to be parasitic in humans and other animals, causing• Lung and vaginal yeast infections • Athlete’s foot
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The Process of Science: Did a Fungus Lead to the Salem Witch Hunt?
– Observation: In 1692, eight young girls were accused of being witches and had symptoms consistent with ergot poisoning.
– Question: Did an ergot outbreak cause the witch hunt?– Hypothesis: The girls’ symptoms were the result of ergot
poisoning.– Prediction: The historical facts would be consistent with
this hypothesis.
© 2010 Pearson Education, Inc.
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– Results:• Agricultural records from 1691, before the symptoms appeared,
indicated a particularly warm and wet year, in which ergot thrives.
• Records from the following year, when accusations of witchcraft died down, indicate a dry year consistent with an ergot die-off.
• This correlation is consistent with the hypothesis but not conclusive.
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Commercial Uses of Fungi
– Fungi are commercially important. Humans eat them and use them to• Produce medicines such as penicillin• Decompose wastes• Produce bread, beer, wine, and cheeses
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Truffles(the fungal kind, not the chocolates)
Blue cheese
Chanterellemushrooms
Figure 16.26
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Penicillium Zone of inhibited growth
Staphylococcus
Figure 16.27
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– Examples of mutually beneficial symbiotic relationships involving fungi include • Mycorrhizae, the association of fungi and plant roots• Lichens, the association of fungi and algae
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Algal cell
Fungalhyphae
Colo
rized
SEM
Figure 16.28