OG-29

tokyolove

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 unicellu-

lar 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 respec-

tive forms. For example, the amino acid sequences of vari-

ous 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

(20) that the tree of life had only two stems. Moreover, argu-

ments pointing out the extent of both structural and func-

tional 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 deter-

mining 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 ances-

tral versions of genes. These techniques have strongly

suggested that although the true bacteria indeed form a

large coherent group, certain other bacteria, the archaebac-

teria, 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.

大家说说排除b的原因是什么？难道是species没有在文中提到？

(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 respec-

tive forms. For example, the amino acid sequences of vari-

ous 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

(20) that the tree of life had only two stems. Moreover, argu-

ments pointing out the extent of both structural and func-

tional 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 deter-

mining 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 ances-

tral versions of genes. These techniques have strongly

suggested that although the true bacteria indeed form a

large coherent group, certain other bacteria, the archaebac-

teria, 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.

大家说说排除b的原因是什么？难道是species没有在文中提到？

[此贴子已经被作者于2006-8-16 12:16:20编辑过]

charmant

C里哪有species阿

tokyolove

为什么发贴之后 总有重复呢！！！！！！！！

后面删除了重复的部分还是不行。。。。

各位大侠请赐教！

ecochem

第一段说生物可以分为E和true bacteria即P，这一段在讲生物分类，没有提到对bacteria的species进行分类

第二段说引入了new techniques, 生物分类要发生变化，当初划在P的范围内的生物其实是不同的，除了true bacteria还有certain other bacteria，要将它们分开。

对于B，错误有二，第一，原文没有提到对bacteria的species分类；第二，既然在new techniques前没有分类，那在new techniques引入后，何来的reclassified?