soon什么意思25个考研英语阅读经典试题及答案(12)生物学类

2021年1月20日发(作者：cstar)

25
个考研英语阅读经典试题及答案
(12)
SAMPLE 12
[
生物学类
]
题目序号题型归类

第
1
题细节推导题型

第
2
题写作手法题型

第
3
题审题定位与中心主旨题型

第
4
题词汇题型

第
5
题审题定位题型

Flatfish, such as the flounder, are among the few vertebrates that lack approximate bilateral
symmetry
(symmetry
in
which
structures
to
the
left
and
right
o
f
the
body’s
midline
are
mirror
images). Most striking among the many asymmetries evident in an adult flatfish is eye placement:
before maturity one eye migrates, so that in an adult flatfish both eyes are on the same side of the
head.
While
in
most
species
with
asymmetries
virtually
all
adults
share
the
same
asymmetry,
members of the starry flounder species can be either left-eyed (both eyes on the left side of head)
or right-eyed. In the waters between the United States and Japan, the starry flounder populations
vary from about 50 percent left-eyed off the United States West Coast, through about 70 percent
left-eyed
halfway
between
the
United
States
and
Japan,
to
nearly
100
percent
left-eyed
off
the
Japanese coast.
Biologists call this kind of gradual vari
ation over a certain geographic range a “cline” and
interpret
clines
as
strong
indications
that
the
variation
is
adaptive,
a
response
to
environmental
differences. For the starry flounder this interpretation implies that a geometric difference (between
fish that are mirror images of one another) is adaptive, that left-eyedness in the Japanese starry
flounder
has
been
selected
for,
which
provokes
a
perplexing
question:
what
is
the
selective
advantage in having both eyes on one side rather than on the other?


The
ease
with
which
a
fish
can
reverse
the
effect
of
the
sidedness
of
its
eye
asymmetry
simply
by
turning
around
has
caused
biologists
to
study
internal
anatomy,
especially
the
optic
nerves, for the answer. In all flatfish the optic nerves cross, so that the right optic nerve is joined to
the
brain’s
left
side
and
vice
versa.
This
crossing
introduces
an
asymmetry,
as
one
optic
nerve
must cross above or below the other. G. H. Parker reasoned that if, for example, a flatfish’s left
eye migrated when the right optic nerve was on top, there would be a twisting of nerves, which
might be mechanically disadvantageous. For starry flounders, then, the left-eyed variety would be
selected against, since in a starry flounder the left optic nerve is uppermost.
The problem with the above explanation is that the Japanese starry flounder population is
almost
exclusively
left-eyed,
and
natural
selection
never
promotes
a
purely
less
advantageous
variation.
As
other explanations
proved
equally
untenable,
biologists
concluded
that
there
is
no
important
adaptive
difference
between
left-eyedness
and
right-eyedness,
and
that
the
two
characteristics
are
genetically
associated
with
some
other
adaptively
significant
characteristic.
This
situation
is
one
commonly
encountered
by
evolutionary
biologists,
who
must
often
decide
whether
a
characteristic
is
adaptive
or
selectively
neutral.
As
for
the
left-eyed
and
right-eyed
flatfish, their difference, however striking, appears to be an evolutionary red herring.
1.
According
to
the
text,
starry
flounder
differ
form
most
other
species
of
flatfish
in
that
starry flounder
[A] are not basically bilaterally symmetric.
[B] do not become asymmetric until adulthood.
[C] do not all share the same asymmetry.
[D] have both eyes on the same side of the head.
2. Which of the following best describes the organization of the text as a whole?
[A] A phenomenon is described and an interpretation presented and rejected.
[B] A generalization is made and supporting evidence is supplied and weighed.
[C] A contradiction is noted and a resolution is suggested and then modified.
[D] A series of observations is presented and explained in terms of the dominant theory.