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Passage 29
It was once assumed that all living things could be
divided into two fundamental and exhaustive categories.
Multicellular plants and animals, as well as many unicellular
organisms, are eukaryotic—their large, complex cells
(5) have a well-formed nucles and many organelles. On the
other hand, the true bacteria are prokaryotic cell, which
are simple and lack a nucleus. The distinction between
eukaryotes and bacteria, initially defined in terms of
subcellular structures visible with a microscope, was ulti-
(10) mately carried to the molecular level. Here prokaryotic and
eukaryotic cells have many features in common. For
instance, they translate genetic information into proteins
according to the same type of genetic coding. But even
where the molecular processes are the same, the details in
(15) the two forms are different and characteristic of the respective
forms. For example, the amino acid sequences of various
enzymes tend to be typically prokaryotic or eukaryotic.
The differences between the groups and the similarities
within each group made it seem certain to most biologists
274
(20) that the tree of life had only two stems. Moreover, arguments
pointing out the extent of both structural and functional
differences between eukaryotes and true bacteria
convinced many biologists that the precursors of the
eukaryotes must have diverged from the common
(25)ancestor before the bacteria arose.
Although much of this picture has been sustained by
more recent research, it seems fundamentally wrong in one
respect. Among the bacteria, there are organisms that are
significantly different both from the cells of eukaryotes and
(30)from the true bacteria, and it now appears that there are
three stems in the tree of life. New techniques for determining
the molecular sequence of the RNA of organisms
have produced evolutionary information about the degree
to which organisms are related, the time since they diverged
(35) from a common ancestor, and the reconstruction of ancestral
versions of genes. These techniques have strongly
suggested that although the true bacteria indeed form a
large coherent group, certain other bacteria, the archaebacteria,
which are also prokaryotes and which resemble true
(40) bacteria, represent a distinct evolutionary branch that
far antedates the common ancestor of all true bacteria. 179. If the “new techniques” mentioned in line 31 were applied in studies of biological classifications other than
bacteria, which of the following is most likely?
(A) Some of those classifications will have to be reevaluated.
(B) Many species of bacteria will be reclassified
(C) It will be determined that there are four main categories of living things rather than three.
(D) It will be found that true bacteria are much older than eukaryotes.
(E) It will be found that there is a common ancestor of the eukaryotes, archaebacteria, and true bacteria. 179. The best answer is A. This question requires you to select the answer that, based on information presented in the passage, describes the most likely result of applying the “new techniques” (lines 31) to biological classifications other than bacteria. Lines 31-36 state that these techniques “produced…information about the degree to which organisms are related.” Specifically, the techniques “strongly suggested” that the prokaryotes category includes two distinct kinds of organisms (lines 36-37). This information, which suggests a reevaluation of the prokaryote classification, provides support for the statement that “classification other than bacteria’ are also likely to require reevaluation if the same techniques are used to study them, as A states. 为什么选A啊,是不是说如果新的技术应用在biological classifications 上结果和新技术应用在bacteria上一样,都会引起分类的重新评估 可是着有什么逻辑联系么,难道说新技术在bacteria上的作用也作用于biological classifications 么? 这题是用文中已有的逻辑联系例证套用到更广泛的例证范围么  | 
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发表于 2007-7-14 23:51:00
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