各位前辈大牛们，我有一个小疑问哈，看小安阅读法时有个练习题，练习里卖包含了杨继的63篇阅读。说实在我觉得这63篇确实挺难的。而且很多文章读懂了也筛选不出答案。各位前辈能不能指导一下阅读究竟该怎么对待杨继63吗吗吗？以这篇为例，麻烦大家了，该怎么分析文章呢？
Nearly a century ago, biologists found thatif they separated an invertebrate animal embryo into two parts at an earlystage of its life, it would survive and develop as two normal embryos. This ledthem to believe that the cells in the early embryo are undetermined in thesense that each cell has the potential to develop in a variety of differentways. Later biologists found that the situation was not so simple. It mattersin which plane the embryo is cut. If it is cut in a plane different from theone used by the early investigators, it will not form two whole embryos. A debate arose over what exactly washappening. Which embryo cells are determined, just when do they becomeirreversibly committed to their fates, and what are the “morphogeneticdeterminants” that tell a cell what to become? But the debate could not beresolved because no one was able to ask the crucial questions in a form inwhich they could be pursued productively. Recent discoveries in molecularbiology, however, have opened up prospects for a resolution of the debate. Nowinvestigators think they know at least some of the molecules that act asmorphogenetic determinants in early development. They have been able to showthat, in a sense, cell determination begins even before an egg is fertilized. Studying sea urchins, biologist Paul Grossfound that an unfertilized egg contains substances that function asmorphogenetic determinants. They are located in the cytoplasm of the egg cell;i.e., in that part of the cell’s protoplasm that lies outside of the nucleus.In the unfertilized egg, the substances are inactive and are not distributedhomogeneously. When the egg is fertilized, the substances become active and,presumably, govern the behavior of the genes they interact with. Since thesubstances are unevenly distributed in the egg, when the fertilized eggdivides, the resulting cells are different from the start and so can bequalitatively different in their own gene activity. The substances that Gross studied arematernal messenger RNA’s—products of certain of the maternal genes. He andother biologists studying a wide variety of organisms have found that theseparticular RNA’s direct, in large part, the synthesis of histones, a class ofproteins that bind to DNA. Once synthesized, the histones move into the cellnucleus, where section of DNA wrap around them to form a structure thatresembles beads, or knots, on a string. The beads are DNA segments wrappedaround the histones; the string is the intervening DNA. And it is the structureof these beaded DNA strings that guide the fate of the cells in which they arelocated. 1. Thepassage is most probably directed at which kind of audience? (A) State legislators deciding aboutfunding levels for a state-funded biological laboratory (B) Scientists specializing in moleculargenetics (C) Readers of an alumni newsletterpublished by the college that Paul Gross attended (D) Marine biologists studying theprocesses that give rise to new species (E) Undergraduate biology majors in amolecular biology course 2. Itcan be inferred from the passage that the morphogenetic determinants present inthe early embryo are (A) located in the nucleus of the embryocells (B) evenly distributed unless the embryo isnot developing normally (C) inactive until the embryo cells becomeirreversibly committed to their final function (D) identical to those that were alreadypresent in the unfertilized egg (E) present in larger quantities than isnecessary for the development of a single individual 3. Themain topic of the passage is (A) the early development of embryos oflower marine organisms (B) the main contribution of modernembryology to molecular biology (C) the role of molecular biology indisproving older theories of embryonic development (D) cell determination as an issue in thestudy of embryonic development (E) scientific dogma as a factor in therecent debate over the value of molecular biology 4. Accordingto the passage, when biologists believed that the cells in the early embryowere undetermined, they made which of the following mistakes? (A) They did not attempt to replicate theoriginal experiment of separating an embryo into two parts. (B) They did not realize that there was aconnection between the issue of cell determination and the outcome of theseparation experiment. (C) They assumed that the results ofexperiments on embryos did not depend on the particular animal species used forsuch experiments. (D) They assumed that it was crucial toperform the separation experiment at an early stage in the embryo’s life. (E) They assumed that different ways ofseparating an embryo into two parts would be equivalent as far as the fate ofthe two parts was concerned. 5. Itcan be inferred from the passage that the initial production of histones afteran egg is fertilized takes place (A) in the cytoplasm (B) in the maternal genes (C) throughout the protoplasm (D) in the beaded portions of the DNAstrings (E) in certain sections of the cell nucleus 6. Itcan be inferred from the passage that which of the following is dependent onthe fertilization of an egg? (A) Copying of maternal genes to producematernal messenger RNA’s (B) Synthesis of proteins called histones (C) Division of a cell into its nucleus andthe cytoplasm (D) Determination of the egg cell’spotential for division (E) Generation of all of a cell’smorphogenetic determinants 7. Accordingto the passage, the morphogenetic determinants present in the unfertilized eggcell are which of the following? (A) Proteins bound to the nucleus (B) Histones (C) Maternal messenger RNA’s (D) Cytoplasm (E) Nonbeaded intervening DNA 8. Thepassage suggests that which of the following plays a role in determiningwhether an embryo separated into two parts will develop as two normal embryos? I. Thestage in the embryo’s life at which the separation occurs II. Theinstrument with which the separations is accomplished III. Theplane in which the cut is made that separates the embryo (A) I only (B) II only (C) I and II only (D) I and III only (E) I, II, and III 9. Whichof the following circumstances is most comparable to the impasse biologistsencountered in trying to resolve the debate about cell determination (lines 12-18)? (A) The problems faced by a literary scholarwho wishes to use original source materials that are written in an unfamiliarforeign language (B) The situation of a mathematician who inpreparing a proof of a theorem for publication detects a reasoning error in theproof (C) The difficulties of a space engineerwho has to design equipment to function in an environment in which it cannotfirst be tested (D) The predicament of a linguist trying todevelop a theory of language acquisition when knowledge of the structure oflanguage itself is rudimentary at best (E) The dilemma confronting a foundationwhen the funds available to it are sufficient to support one of two equallydeserving scientific projects but not both
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发表于 2013-5-31 18:25:31
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