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passage 3
P1
A lichen consists of a fungus living in symbiosis (i.e., a mutually beneficial relationship) with an alga. ████████ ████ ████████ ██ ███ ███████ ████████████ ██████ ████ ██ █████ ████ ████ ████ ████████████ ███ ████████████ ███████ ██ ██████████████ █████ ████ ████ █ ████████ ███
Intro topic / phenomenon ·
What's the evolutionary origin of lichen?
Lichen is a fungus living in a mutually beneficial relationship with an alga.
Hypothesis ·
New study shows lichen are close relatives of certain common fungi
That's why some lichen look like mushrooms.
P2
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Why lichen was hard to classify ·
Hard to study their DNA
Fungi are usually in a parasitic or symbiotic relationship with another organism. Hard to tell DNA apart. Lichen in particular are hard to isolate from their associated organism.
Old classification ·
Lichen were considered separate from other fungi with unknown origin
New classification ·
Some lichen belong to fungus family tree
New tools allowed us to isolate lichen-fungi DNA from their associated organisms. Researchers think we'll find that more types of lichen belong to additional branches of the fungus family tree.
P3
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Implication ·
Provides evidence that parasitic interactions don't always evolve over time to help host organisms
Fungi that are both harmful and helpful to the host organism are found throughout fungus evolutionary history. We know this because lichen, which are beneficial to their host organism, are found in different positions throughout the family tree. (So there's some kind of back and forth harmful-to-host, helpful-to-host, harmful-to-host development in the fungus family tree.)
Passage Style
Phenomenon-hypothesis
Single position
15.
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a
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b
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c
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d
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e
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