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发表于 2005-10-3 16:30:11
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no8-3-3
(This passage is excerpted from
an article that was published in 1981.)
The deep sea typically has a sparse
fauna dominated by tiny worms and
(5) crustaceans, with an even sparser
distribution of larger animals. However,
near hydrothermal vents, areas of the
ocean where warm water emerges from
subterranean sources, live remarkable
(10) densities of huge clams, blind crabs,
and fish. Most deep-sea faunas rely for
food on particulate matter, ultimately
derived from photosynthesis, falling
from above. The food supplies necessary
(15) to sustain the large vent communities,
however, must be many times the
ordinary fallout. The first reports
describing vent faunas proposed two
possible sources of nutrition: bacterial
(20) chemosynthesis, production of food by
bacteria using energy derived from
chemical changes, and advection, the
drifting of food materials from
surrounding regions. Later, evidence in
(25) support of the idea of intense local
chemosynthesis was accumulated:
hydrogen sulfied was found in vent
water; many vent-site bacteria were
found to be capable of chemosynthesis;
(30) and extremely large concentrations of
bacteria were found in samples of vent
water thought to be pure. This final
observation seemed decisive. If such
astonishing concentrations of bacteria
(35) were typical of vent outflow, then
food within the vent would dwarf any
contribution from advection. Hence,
the widely quoted conclusion was
reached that bacterial chemosynthesis
(40) provides the foundation for
hydrothermal- vent food chains—an
exciting prospect because no other
communities on Earth are independent
of photosynthesis.
(45) There are, however, certain difficul-
ties with this interpretation.For example,
some of the large sedentary organisms
associated with vents are also found at
ordinary deep-sea temperatures many
(50) meters from the nearest hydrothermal
sources. This suggests that bacterial
chemosynthesis is not a sufficient
source of nutrition for these creatures.
Another difficulty is that similarly
(55) dense populations of large deep-sea
animals have been found in the
proximity of "smokers"–vents where
water emerges at temperatures up to
350°C. No bacteria can survive such
(60) heat, and no bacteria were found there.
Unless smokers are consistently
located near more hospitable warm-water
vents, chemosynthesis can account for
only a fraction of the vent faunas.
(65) It is conceivable, however, that
these large, sedentary organisms do
in fact feed on bacteria that grow in
warm-water vents, rise in the vent
water, and then rain in peripheral areas
(70) to nourish animals living some distance
from the warm-water vents.
Nonetheless advection is a more likely
alternative food source. Research has
demonstrated that advective flow, which
(75) originates near the surface of the ocean
where suspended particulate matter
accumulates, transports some of that
matter and water to the vents. Estimates
suggest that matter and water to the
(80) vents. Estimates suggest that for every
cubic meter of vent discharge, 350
milligrams of particulate organic
material would be advected into the
vent area. Thus, for an average-sized
(85) vent, advection could provide more
than 30 kilograms of potential food per
day. In addition, it is likely that small
live animals in the advected water might
be killed or stunned by thermal and/or
(90) chemical shock, thereby contributing to
the food supply of vents.
The passage provides information for
answering which of the following
questions?
What causes warm-water vents to form?
Do vent faunas consume more than do
deep-sea faunas of similar size?
Do bacteria live in the vent water of
smokers?
What role does hydrogen sulfide play
in chemosynthesis?
What accounts for the locations of
deep-sea smokers?
The information in the passage
suggests that the majority of deep-sea
faunas that live in nonvent habitats
have which of the following
characteristics?
They do not normally feed on particles
of food in the water.
They are smaller than many vent faunas.
They are predators.
They derive nutrition from a chemosynthetic
food source.
They congregate around a single main
food source.
The primary purpose of the passage
is to
describe a previously unknown natural
phenomenon
reconstruct the evolution of a natural
phenomenon
establish unequivocally the accuracy
of a hypothesis
survey explanations for a natural
phenomenon and determine which is best
supported by evidence
entertain criticism of the author's
research and provide an effective response
Which of the following does the author
cite as a weakness in the argument that
bacterial chemosynthesis provides the
foundation for the food chains at deep-
sea vents?
Vents are colonized by some of
the same animals found in other areas
of the ocean floor.
Vent water does not contain
sufficient quantities of hydrogen
sulfide.
Bacteria cannot produce large
quantities of food quickly enough.
Large concentrations of minerals
are found in vent water.
Some bacteria found in the vents
are incapable of chemosynthesis.
————————————————————————
Which of the following is information
supplied in the passage that would support
the statement that the food supplies
necessary to sustain vent communities
must be many times that of ordinary
fallout?
I. Large vent faunas move from vent to
vent in search of food.
II. Vent faunas are not able to consume
food produced by photosynthesis.
III. Vents are more densely populated
than are other deep-sea areas.
I only
III only
I and II only
II and III only
I, II, and III
————————————————————————
The author refers to "smokers"
(line 57) most probably in order to
show how thermal shock can provide
food for some vent faunas by stunning
small animals
prove that the habitat of most deep-
sea animals is limited to warm-water
vents
explain how bacteria carry out
chemosynthesis
demonstrate how advection compensates
for the lack of food sources on the
seafloor
present evidence that bacterial
chemosynthesis may be an inadequate
source of food for some vent faunas
————————————————————————
Which of the following can be inferred
from the passage about the particulate
matter that is carried down from the
surface of the ocean?
It is the basis of bacterial
chemosynthesis in the vents.
It may provide an important source
of nutrition for vent faunas.
It may cause the internal temperature
of the vents to change significantly.
It is transported as large aggregates
of particles.
It contains hydrogen sulfide.
————————————————————————
Throughout human history there have
been many stringent taboos concerning
watching other people eat or eating
in the presence of others. There have
(5) been attempts to explain these taboos
in terms of inappropriate social
relationships either between those
who are involved and those who are
not simultaneously involved in the
(10) satisfaction of a bodily need, or
between those already satiated and
those who appear to be shamelessly
gorging.
Undoubtedly such elements exist in
(15) the taboos, but there is an additional
element with a much more fundamental
importance. In prehistoric times, when
food was so precious and the on-lookers
so hungry, not to offer half of the
(20) little food one had was unthinkable,
since every glance was a plea for life.
Further, during those times, people
existed in nuclear or extended family
groups, and the sharing of food was
(25) quite literally supporting one's family
or, by extension, preserving one's self.
If the argument in the passage is
valid, taboos against eating in the
presence of others who are not also
eating would be LEAST likely in a
society that
had always had a plentiful supply
of food
emphasized the need to share worldly
goods
had a nomadic rather than an
agricultural way of life
emphasized the value of privacy
discouraged overindulgence
————————————————————————
The author's hypothesis concerning
the origin of taboos against watching
other people eat emphasizes the
general palatability of food
religious significance of food
limited availability of food
various sources of food
nutritional value of food
————————————————————————
According to the passage, the author
believes that past attempts to explain
some taboos concerning eating are
unimaginative
implausible
inelegant
incomplete
unclear
————————————————————————
In developing the main idea of the
passage, the author does which of the
following?
Downplays earlier attempts to
explain the origins of a social
prohibition.
Adapts a scientific theory and
applies it to a spiritual relationship.
Simplifies a complex biological
phenomenon by explaining it in terms
of social needs.
Reorganizes a system designed to
guide personal behavior.
Codifies earlier, unsystematized
conjectures about family life.
———————————————————————— |
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