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
2025-02-26
9
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] According to the passage, investigations of eukaryotic and prokaryotic cells at the molecular level supported the conclusion that
选项
A、most eukaryotic organisms are unicellular.
B、complex cells have well-formed nucles.
C、prokaryotes and eukaryotes form two fundamental categories.
D、subcellular structures are visible with a microscope.
E、prokaryotic and eukaryotic cells have similar enzymes.
答案
C
解析
在分子级别对真核、原核细胞的研究支持以下哪个结论?A.大部分真核生物单细胞。荒谬。B.复杂细胞有完整细胞核。只是真核细胞有。complex cell和eukaryotic这两个概念不能随便互换。C.正确。原核、真核组成两个基本种类。见原文L10—15,这种二分法最终要以在分子层面得以证实。D.此选项和本文内容无关。E.原核。真核有相似的酶。说反了。L23~26,酶的序列可分为原核型和真核型。
转载请注明原文地址:https://tihaiku.com/zcyy/3973808.html
相关试题推荐
Itwasonceassumedthatalllivingthingscouldbedividedintotwofundame
Itwasonceassumedthatalllivingthingscouldbedividedintotwofundame
Itwasonceassumedthatalllivingthingscouldbedividedintotwofundame
Itiswidelyassumedthatamuseumishelpedfinanciallywhenagenerouspatron
Peoplecannotbemorallyresponsibleforthingsoverwhichtheyhavenocontrol.
Becausedinosaurswerereptiles,scientistsonceassumedthat,likeallreptiles
Onturning65yearsold,everyonelivinginthetownofMaltonbecomeseligible
Roger:Readingalotasachildcausesnearsightedness—difficultyseeingthings
Accordingtoarecentpoll,owningandlivinginafreestandinghouseonitsown
OutofAmerica’sfascinationwithallthingsantiquehavegrownamarketforbyg
随机试题
Mostpeoplepicturesharks【C1】______huge,powerful,frightening【C2】______rea
QualityAssuranceatAllStagesWerecognizethatth
TheplaywrightDavidHenryHwanghasbeeninhighdemandinrecentyears—not
DoctorsinBritainarewarningofanobesity(肥胖症)timebomb,whenchildren
直接导致“魔弹”被否定的理论是()A.有限效果论 B.新的强效力论 C.适
某液化石油气库建于1998年,位于某县,临江而设,交通便利,环境较好。该石油气库
关于自身免疫和自身免疫病的叙述错误的是A.机体对自身抗原产生免疫应答都会产生不利
J113、查找220V直流系统接地使用表计的内阻应()。(A)不小于20
政府采购的内容包括货物、工程和( )。A.原材料 B.服务 C.设备 D
根据《建设工程施工合同示范文本》,当出现专用合同条款规定的异常恶劣气候导致工期延
最新回复
(
0
)