A lichen consists of a fungus living in symbiosis (i.e., a mutually be

A lichen consists of a fungus living in symbiosis
(i.e., a mutually beneficial relationship) with an alga.
Although most branches of the complex evolutionary
family tree of fungi have been well established, the
(5) evolutionary origins of lichen-forming fungi have
been a mystery. But a new DNA study has revealed
the relationship of lichen-forming fungi to several
previously known branches of the fungus family tree.
The study reveals that, far from being oddities,
(10) lichen-forming fungi are close relatives of such
common fungi as brewer’s yeast, morel mushrooms,
and the fungus that causes Dutch elm disease. This
accounts for the visible similarity of certain lichens to
more recognizable fungi such as mushrooms.

(15) In general, fungi present complications for the
researcher. Fungi are usually parasitic or symbiotic,
and researchers are often unsure whether they are
examining fungal DNA or that of the associated
organism. But lichen-forming fungi are especially
(20) difficult to study. They have few distinguishing
characteristics of shape or structure, and they are
unusually difficult to isolate from their partner algae,
with which they have a particularly delicate
symbiosis. In some cases the alga is wedged between
(25) layers of fungal tissue; in others, the fungus grows
through the alga’s cell walls in order to take
nourishment, and the tissues of the two organisms are
entirely enmeshed and inseparable. As a result,
lichen-forming fungi have long been difficult to
(30) classify definitively within the fungus family. By
default they were thus considered a separate grouping
of fungi with an unknown evolutionary origin. But,
using new analytical tools that allow them to isolate
the DNA of fungi in parasitic or symbiotic
(35) relationships, researchers were able to establish the
DNA sequence in a certain gene found in 75 species
of fungi, including 10 species of lichen-forming
fungi. Based on these analyses, the researchers found
5 branches on the fungus family tree to which
(40) varieties of lichen-forming fungi belong. Furthermore,
the researchers stress that it is likely that as more
types of lichen-forming fungi are analyzed, they will
be found to belong to still more branches of the
fungus family tree.

(45) One implication of the new research is that it
provides evidence to help overturn the long-standing
evolutionary assumption that parasitic interactions
inevitably evolve over time to a greater benignity and
eventually to symbiosis so that the parasites will not
(50) destroy their hosts. The addition of lichen-forming
fungi to positions along branches of the fungus
family tree indicates that this assumption does not
hold for fungi. Fungi both harmful and benign can
now be found both early and late in fungus
(55) evolutionary history. Given the new layout of the
fungus family tree resulting from the lichen study, it
appears that fungi can evolve toward mutualism and
then just as easily turn back again toward parasitism.

1. Which one of the following most accurately states the main point of the passage?

(A) New research suggests that fungi are not only parasitic but also symbiotic organisms.
(B) New research has revealed that lichen-forming fungi constitute a distinct species of fungus.
(C) New research into the evolutionary origins of lichen-forming fungi reveals them to be closely related to various species of algae.
(D) New research has isolated the DNA of lichenforming fungi and uncovered their relationship to the fungus family tree.
(E) New research into the fungal component of lichens explains the visible similarities between lichens and fungi by means of their common evolutionary origins.


2. Which one of the following most accurately describes the author’s purpose in the last paragraph of the passage?

(A) to suggest that new research overturns the assumption that lichen-forming fungi are primarily symbiotic, rather than parasitic, organisms
(B) to show that findings based on new research regarding fungus classification have implications that affect a long-standing assumption of evolutionary science
(C) to explain the fundamental purposes of fungus classification in order to position this classification within the broader field of evolutionary science
(D) to demonstrate that a fundamental assumption of evolutionary science is verified by new research regarding fungus classification
(E) to explain how symbiotic relationships can evolve into purely parasitic ones


3. Which one of the following most accurately describes the organization of the passage?

(A) explanation of the difficulty of classifying lichens; description of the DNA sequence of lichen-forming fungi; summary of the implications of this description
(B) definition of lichens; discussion of new discoveries concerning lichens’ evolutionary history; application of these findings in support of an evolutionary theory
(C) definition of lichens; discussion of the difficulty in classifying their fungal components; resolution of this difficulty and implications of the resulting research
(D) discussion of the symbiotic relationship that constitutes lichens; discussion of how new research can distinguish parasitic from symbiotic fungi; implications of this research
(E) explanation of the symbiotic nature of lichens; discussion of the problems this poses for genetic researchers; delineation of the implications these problems have for evolutionary theory


4. According to the passage, the elimination of which one of the following obstacles enabled scientists to identify the evolutionary origins of lichen-forming fungi?

(A) The DNA of lichen-forming fungi was not easy to separate from that of their associated algae.
(B) Lichen-forming fungi are difficult to distinguish from several common fungi with which they are closely related.
(C) Lichen-forming fungi were grouped separately from other fungi on the fungus family tree.
(D) Lichen-forming fungi are far less common than more recognizable fungi such as mushrooms.
(E) The DNA of lichen-forming fungi is significantly more complex than that of other fungi.


5. Which one of the following, if true, most weakens the author’s criticism of the assumption that parasitic interactions generally evolve toward symbiosis?

(A) Evolutionary theorists now postulate that symbiotic interactions generally evolve toward greater parasitism, rather than vice versa.
(B) The evolutionary tree of fungi is somewhat more complex than that of similarly parasitic or symbiotic organisms.
(C) The DNA of fungi involved in symbiotic interactions is far more difficult to isolate than that of fungi involved in parasitic interactions.
(D) The placement of lichen-forming fungi as a separate group on the fungus family tree masked the fact that parasitic fungi sometimes evolved much later than symbiotic ones.
(E) Branches of the fungus family tree that have evolved from symbiosis to parasitism usually die out shortly thereafter.