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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Question 1 The main purpose of the passage is to