12.Practice.Tests.for.the.SAT_2015-2016_1128p

Section 71
Practice Test Three
267
Directions: The passages below are follo':ed b'. questions based on their content; questions following a pair of related
passaes may als be ?asd on the relationship between the paired passages. Answer the questions on the basis of
what is stated or implied m the passages and in any introductory material that may be provided.
Questions 8-19 are based on the following passage.
The fo llowing passage is adapted from an article on the
importance of bacteria to modern life.
There is a whole category of life that is fascinating,
versatile, useful, and surprisingly varied
and populous, and it's overlooked by a majority
Line of people. Bacteria make up one and possibly
( 5) two overarching categories of life, as biologists
currently classify it. Prokaryotes, or true bacteria,
are organisms without an organized cell
nucleus. Archaebacteria were originally classified
as prokaryotes, but recent studies have revealed
(10) differences in their cellular structure that might
necessitate a whole new category to describe them.
Bacteria are incredibly numerous; it may be that
all the species we have ever catalogued make up
only 5 percent of the total number of species
( 15) of bacteria. They are everywhere in our world,
from our dirt to our food to the very insides of
our bodies. The fact that we can't see them makes
them easy to ignore, but their impact on our lives
is undeniable and probably extends into more
(20) aspects of living than scientists are currently even
aware of.
Perhaps the most remarkable thing about bacteria
is their ability to survive in extreme environmental
conditions. The oldest fossils scientists
(25) have discovered are fossilized bacteria; they were
on Earth when the planet was unbearably hot
and carried no oxygen in its atmosphere. It was
through bacteria evolving to adapt the sun's light
into nutrients, and their subsequent development
(30) of the same kind of photosynthesis that plants
use today, that oxygen and carbon dioxide were
introduced to our atmosphere as waste products,
allowing plants and animals to find a toehold on
an otherwise inhospitable planet.
(35) One thing that makes bacteria such hardy survivors
is their ability to alter their living DNA by
exchanging their own with that in the environment
around them or with that of other bacteria
using methods called, respectively, transformation
(40) and conjugation. In this way, they can acquire
the genes necessary to protect themselves from
extreme conditions like exceptionally hot, acidic,
or airless environments; they can also acquire
resistance to a particular antibiotic from another
( 45) bacterium that already has the resistance. With these
DNA-trading tactics, bacteria can benefit from
evolutionary progress made by other species simply
by assuming it as their own.
The most common response to the word bac-
(50) teria is to think of disease. While bacteria are the
cause of many annoying and deadly diseases, most
species are harmless, and many are actually beneficial.
Bacteria are indispensable to many aspects of
modern industry and production. We use bacteria
(55) to culture cheese and give each type its distinctive
flavor, to treat sewage by breaking down harmful
toxins into methane gas, to extract the desirable
metal from other minerals in mines in a more
environment-friendly alternative to smelting, and
(60) to improve the nutrient absorption and therefore
the yield of food crops. Bacteria are also the basis
for biotechnology; by combining bacteria with
human DNA, we can use bacterial reproduction to
manufacture important hormones like insulin or
(65) antibodies that fight disease.
Despite all their beneficial uses, of course, the
negative impacts of some bacteria cannot be
ignored. While one strain of bacteria might give
your smoked gouda its distinctive flavor, another
(70) species could very well be working on spoiling
it, covering it with mold. Much of the bacteria
in pretreated sewage can cause deadly diseases.
Some bacteria accelerate rusting, especially in
metals containing iron. Other species will kill a
(75) farm's entire crop. If canned food is not heated
to 250° Fahrenheit during preservation, it could
be infected with botulism, a deadly toxin. With all
their dangers, ironically enough, bacteria are supporting
other industries, such as those devoted to
(80) antibacterial cleaning products, sterilization, and
controlling the growth of dangerous species. Our
relationship with bacteria is not a simple one, but
it is an important one and one that is highly if
invisibly ingrained into our daily way of life.
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