Self-study
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 (RC)
Single position
17.
Which one of the following ████ ██████████ █████████ ███ ████████████ ██ ███ ████████
a
explanation of the ██████████ ██ ███████████ ████████ ███████████ ██ ███ ███ ████████ ██ ██████████████ ██████ ███████ ██ ███ ████████████ ██ ████ ███████████
The explanation of the difficulty of classifying lichens comes in P2, not at the beginning.
b
definition of lichens; ██████████ ██ ███ ███████████ ██████████ ████████ ████████████ ████████ ███████████ ██ █████ ████████ ██ ███████ ██ ██ ████████████ ██████
The author doesn’t apply the DNA research to support an evolutionary theory at the end. Rather, the author shows how the DNA research overturns an assumption underlying an aspect of evolutionary theory.
c
definition of lichens; ██████████ ██ ███ ██████████ ██ ███████████ █████ ██████ ███████████ ██████████ ██ ████ ██████████ ███ ████████████ ██ ███ █████████ ████████
This is the best description of the overall organization. There’s a definition of lichen at the beginning, the difficulty of classifying lichen’s fungal components is discussed in P2, resolution of this difficulty comes later in P2, then P3 discusses implications.
d
discussion of the █████████ ████████████ ████ ███████████ ████████ ██████████ ██ ███ ███ ████████ ███ ███████████ █████████ ████ █████████ ██████ ████████████ ██ ████ ████████
The research doesn’t discuss how we can distinguish parasitic from symbiotic fungi.
e
explanation of the █████████ ██████ ██ ████████ ██████████ ██ ███ ████████ ████ █████ ███ ███████ ████████████ ███████████ ██ ███ ████████████ █████ ████████ ████ ███ ████████████ ██████
The symbiotic nature of lichens isn’t why lichens are hard to study. They’re hard to study because they have few distinguishing characteristics and are unusually hard to isolate from their partner algae. In addition, the implications at the end do not result from the problems for genetic researchers; they result from the DNA research that found evidence about the evolutionary origins of lichen.