SAT Reading - Khan Diagnostic Quiz level 3 - reading 17

Questions 1-11 are based on the following passage.

This passage is excerpted from Luis Villareal, “Are Viruses Alive?” © 2008 by Scientific American. The symbol [2004] indicates that the following sentence is referenced in a question.

For about 100 years, the scientific community has
55 repeatedly changed its collective mind over what viruses are.
First seen as poisons, then as life-forms, then biological
Line chemicals, viruses today are thought of as being in a gray
5 area between living and nonliving: they cannot replicate on
their own but can do so in truly living cells and can also
affect the behavior of their hosts profoundly.
The seemingly simple question of whether or not viruses
are alive has probably defied a simple answer all these years
10 because it raises a fundamental issue: What exactly defines
“life?” A precise scientific definition of life is an elusive
thing, but most observers would agree that life includes
certain qualities in addition to an ability to replicate. For
example, a living entity is in a state bounded by birth and
15 death. Living organisms also are thought to require a degree
of biochemical autonomy, carrying on the metabolic
activities that produce the molecules and energy needed to
sustain the organism. This level of autonomy is essential to
most definitions.
20 Viruses, however, parasitize essentially all biomolecular
aspects of life. That is, they depend on the host cell for the
raw materials and energy necessary for nucleic acid
synthesis, protein synthesis, processing and transport, and all
other biochemical activities that allow the virus to multiply
25 and spread. One might then conclude that even though these
processes come under viral direction, viruses are simply non-
living parasites of living metabolic systems. But a spectrum
may exist between what is certainly alive and what is not.
A rock is not alive. A metabolically active sack, devoid of
30 genetic material and the potential for propagation, is also not
alive. A bacterium, though, is alive. Although it is a single
cell, it can generate energy and the molecules needed to
sustain itself, and it can reproduce. But what about a seed?A
seed might not be considered alive. Yet it has a potential for
35 life, and it may be destroyed. In this regard, viruses resemble
seeds more than they do live cells.
Another way to think about life is as an emergent property
of a collection of certain non-living things. Both life and
consciousness are examples of emergent complex systems.
40 They each require a critical level of complexity or interaction
to achieve their respective states. A neuron by itself, or even
in a network of nerves, is not conscious-whole brain
complexity is needed. A virus, too, fails to reach a critical
complexity. So life itself is an emergent, complex state, but it
45 is made from the same fundamental, physical building blocks
that constitute a virus. Approached from this perspective,
viruses, though not fully alive, may be thought of as being
more than inert matter: they verge on life.
In fact, in October [2004], French researchers announced
findings that illustrate afresh just how close some viruses
50 might come. Didier Raoult and his colleagues at the
University of the Mediterranean in Marseille announced that
they had sequenced the genome of the largest known virus,
Mimivirus, which was discovered in 1992. The virus, about
the same size as a small bacterium, infects amoebae.
55 Sequence analysis of the virus revealed numerous genes
previously thought to exist only in cellular organisms. Some
of these genes are involved in making the proteins encoded
by the viral DNA and may make it easier for Mimivirus to
co-opt host cell replication systems. As the research team
60 noted in its report in the journal Science, the enormous
complexity of the Mimivirus’s genetic complement
“challenges the established frontier between viruses and
parasitic cellular organisms.”

 
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