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谁作过RC大全的,是否可以帮忙给出标准答案?谢谢! It is well known that biological changes at the molecular level have morphogenetic consequences, consequences affecting the formation and differentiation of tissues and organs. It is superfluous to point out (point out: v.指出) that gene mutations and disturbances of the bio-synthetic processes in the embryo may result in abnormalities in the morphology (structure) of an organism. However, whereas much is known about causes and consequences at the molecular level, and in spite of an enormous accumulation of chemical and morphological data on embryos of various kinds, our understanding of how genes control morphogenesis is still far from complete. Perhaps one reason for this is that molecular biologists and morphologists speak different languages. Whereas the former speak about messenger-RNA and conformational changes of protein molecules, the latter speak of ectoderms, hypoblasts, and neural crests. One solution to this predicament is to try to find some phenomena relevant to morphogenesis which both the molecular biologist and the morphologist can understand and discuss. As morphogenesis must be basically the result of changes in behavior of the individual cells, it seems logical to ask morphologists to describe the morphogenetic events observed in terms of changes in cellular contact, changes in the rate of proliferation of cells, or similar phenomena. Once this is done, it may be appropriate to ask questions about the molecular background for these changes. One may, for instance, ask whether variations in cell contact reflect alterations in the populations of molecules at the cell surface, or one may inquire about the molecular basis for the increased cell mobility involved in cell dispersion. Studies of this kind have been carried out with cells released from tissues in various ways and then allowed to reveal their behavior after being spread out into a thin layer. In many cases, such cells show the ability to reaggregate, after which different cell types may sort themselves out into different layers and even take part in still more intricate morphogenetic events. But in most cases, the behavior of cells in the intact embryo is difficult to study because of the thickness and opacity of the cell masses. The sea urchin (sea urchin: 海胆) embryo, however, has the advantage that it is so transparent that each cell can be easily observed throughout development. Thus, by recording the development of a sea urchin embryo with time-lapse photography, the research scientist might discover previously unknown features of cellular behavior. Perhaps the study of the sea urchin in this manner can provide a medium by which the molecular biologist and the morphologist can begin communicating with each other more effectively about the way in which genes control morphogenesis. 17. The author’s primary purpose is to (A) outline a procedure and discuss possible applications (B) evaluate an experiment in terms of its applicability to medical research (C) propose a method for curing specific genetic disorders (D) explain a problem and suggest a solution for it（D） (E) reveal the shortcomings of several attitudes toward genetic research 18. The author states that research into the genetic control of morphogenesis has been impeded by (A) an incomplete understanding of biomolecular reactions that are highly complex (B) a lack of communication between scientists whose work could be complementary (C) a reluctance on the part of morphologists to share data with molecular biologists (D) a lack of research in the area of morphology（B） (E) the unavailability of suitable research equipment 19. The major objective of the author’s proposal is to (A) devise a technique for proving that abnormalities in morphology result from gene mutations (B) improve the procedures for organizing chemical and morphological data (C) increase the accuracy of measurements of cell populations and cell mobility (D) reduce the margin of error in the study of conformational changes of protein molecules（E） (E) provide a plan for increasing knowledge about the influence of genes on morphogenesis 20. It can be inferred from the passage that some cells that have been isolated from an organism have the ability to (A) control morphogenesis (B) reform to make higher organisms (C) reorganize to form clusters of cells (D) regulate the transmission of light through the cell wall（C） (E) regulate the rate of tissue formation 21. It can be inferred from the passage that the study of the effects of genes on morphogenesis is best accomplished by observing (A) intact developing embryos (B) adult sea urchins (C) isolated living cells (D) groups of genetically mutated cells（A） (E) cells from the same kink of tissue 22. According to the passage, it is difficult to study cells in most intact embryos because (A) morphogenetic events cannot be isolated (B) embryos die quickly (C) embryos are difficult to obtain (D) individual cells reaggregate too quickly（E） (E) individual cells are difficult to see 23. Which of the following sequences best describes the author’s suggestion for future research on morphogenesis? (A) Accumulation of data, simplification of language, explanation of morphogenesis (B) Dispersion of cells, evaluation of cell activity, development of an explanatory hypothesis (C) Classification of cell types, separation of cell, observation of cell activity (D) Observation of cell development, description of cell behavior, explanation at the molecular level（D） (E) Differentiation of cell types, description of cell structure, analysis of molecular components 24. The tone of the author’s discussion of the difference in the language used by morphologists and that used by molecular biologists is one of (A) indifference (B) neutrality (C) derision (D) approbation（B） (E) indignation | 
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发表于 2006-9-21 16:57:00
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