首页
登录
职称英语
It was once assumed that all living things could be divided into two fundame
It was once assumed that all living things could be divided into two fundame
游客
2024-01-13
32
管理
问题
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 eukary-otic—their large, complex cells have a well-formed nucleus 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 ultimately 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 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 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 ancestor before the bacteria arose.
Although much of this picture has been sustained by more recent research, it seems fundamentally wrong in one re- spect. Among the bacteria, there are organisms that are significantly different both from the cells of eukaryotes and 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 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 co- herent group, certain other bacteria, the archaebacteria, which are also prokaryotes and which resemble true bacteria, represent a distinct evolutionary branch that far antedates the com- mon ancestor of all true bacteria. [br] The author’s attitude toward the view that living things are divided into three categories is best described as one of
选项
A、tentative acceptance.
B、mild skepticism.
C、limited denial.
D、studious criticism.
E、whole hearted endorsement.
答案
A
解析
作者对三分法持什么态度?其基本态度是肯定的。A.正确。谨慎的接受。
转载请注明原文地址:http://tihaiku.com/zcyy/3359252.html
相关试题推荐
Ms.Green______livingintownforonlyoneyear,yetsheseemstoknoweveryone
Ahundredyearsagoitwasassumedandscientifically"proved"byeconomists
Ahundredyearsagoitwasassumedandscientifically"proved"byeconomists
Ahundredyearsagoitwasassumedandscientifically"proved"byeconomists
______workhasbeendonetoimprovepeople’slivingstandard.A、ManyB、Agreatm
_________workhasbeendonetoimprovepeople’slivingstandard.A、ManyB、Agreat
Ahundredyearsagoitwasassumedandscientifically"proved"byeconom
Ahundredyearsagoitwasassumedandscientifically"proved"byeconom
________,worksongsoftenexhibitthesongcultureofapeopleinafundamental
Mistakesarethethingsthatnobodywants,butwestillmakemistakesatany
随机试题
[originaltext]W:Isn’titdelightfulhere?We’vebeenlookingforaplacejust
(1)Punditswhowanttosoundjudiciousarefondofwarningagainstgeneraliz
上述事实启示我们()A.物质决定意识,意识反作用于物质 B.意识对物质有促进作
某居住小区的热源为燃煤锅炉,小区供暖热负荷为10MW,冬季生活热水的最大小时耗热
某公司按总价格合同方式约定订购3000米高规格的铜缆,由于建设单位原因,工期暂停
下列哪位是意大利的男高音?A.维克斯 B.帕瓦罗蒂 C.多明戈 D.卡雷拉
A.混悬剂 B.生理盐水 C.静脉注射脂肪乳剂 D.右旋糖酐注射液 E.
原本乘坐巴士会晕车的人,后来乘船、乘火车等也有类似的反应,这是( )A.条件反
A.无臭,味涩、苦、略回甜 B.气微,味淡 C.微有草腥气,味淡 D.气清
(2020年12月真题)关于中标通知书的说法,正确的有()。A.中标通知书对
最新回复
(
0
)