The antigen-antibody immunological reaction used to be regarded as

The best answer is E. This question asks for the author's primary interest or concern in writing this passage, or the central idea of the passage as a whole. To answer this question, carefully evaluate the first words in the five choices. Choice A begins with " proving"; choice B begins with "establishing." Both of these words may fit the procedure of the passage, but the statements are false. Choice C can be rejected because, although the author states that reluctance to abandon a hypothesis made new research difficult (lines 22-27), the author does not directly criticize scientists. Paragraphs one and three are almost entirely descriptive; therefore, the author's purpose must not be to analyze immunological reactions (choice D) but to explain them (choice E).


The best answer is E. First, examine each of the choices to determine which makes an accurate statement, based on evidence in the passage, about the reasons that scientists had to qualify the antigen-antibody theory. The question refers to line 37, which is part of a sentence that says, in combination with the preceding sentence, that scientists qualified the antigen-antibody theory when they could not explain "how an antigen is recognized " (lines 29-30) and " how a structure exactly complementary to it is then synthesized" (lines 30- 31). From this, scientists realized that the mechanism for directing the synthesis of the antibody did not operate in the way they had thought. The other choices are plausible statements, but they are not relevant to the cause-and-effect relationship asked about in the question.


The best answer is D. The author mentions "difficulties" with the theory but does not call it " wrong ." Therefore, A is incorrect. The author refers to two important manifestations of the antigen-antibody reactions in the first paragraph, and so does not believe, as B states, that the theory " was accepted without evidence," or, as C states, " is unverifiable." Nowhere does the author suggest, as E states, that the theory "has been a divisive issue among scientists." Lines 37-43 do state that research "led scientists to realize that a second immunological reaction" also takes place in the body. Thus, scientists realized that the antigen-antibody theory was, as choice D states, "a partial explanation."


The best answer is C. This questions asks you to gather from the first two paragraphs the processes the author attributes to antigen-antibody reactions, and then to recognize which of the choices is not mentioned in the passage. Choice A, synthesis of a protein, is mentioned in lines 3-6. Choice B, activation of complement in the bloodstream, is mentioned in lines 15-18. Choice D, entrapment of antigens by macrophages, is explained as phagocytosis in lines 12-14. Choice E, formation of a substance with a structure complementary to that of an antigen, is discussed in paragraph two, lines 28-31, as part of the"primary difficulty" of the antigen-antibody theory. The only choice not mentioned in the passage is the destruction of antibodies. Therefore, the best answer is choice C.


The best answer is A. The format of this question requires you to evaluate each of the questions designated with Roman numerals separately and carefully. The question I is answered by paragraph three, which indicates that, in cell-mediated immunological reactions, lymphocytes do not produce antibodies but destroy foreign tissue cells by themselves. Nowhere does the passage answer question II; it does not discuss why lymphocytes are more hostile to antigens during cell-mediated reactions than are other cell groups. Nor does the passage answer question III; it does not compare the cell-mediated reaction involved in transplants to the cell-mediated reaction involved in parasite invasion; instead, the passage simply states that the reaction occurs in both cases. Therefore, the passage answers question I only.


The best answer is B. According to the passage, scientists arrived at the theory of cell-mediated immunological reactions because the theory of antigen-antibody immunological reaction could not explain how an antibody, which is made of protein, could recognize and synthesize another protein (lines 27-37). It can be inferred that scientists might not have developed the theory of cell-mediated immunological reactions if they had discovered the reverse -- that proteins could direct the synthesis of other proteins.


The best answer is A. The question requires you to compare the information given in the passage about antigen-antibody responses to the information given in the passage about cell-
. mediated responses, and to decide which of the Roman numeral choices the two reactions have in common. The choice I, the destruction of antigens, is discussed in paragraph one and paragraph two in connection with both types of immunological reaction. Choice II, the creation of antibodies, is discussed in paragraph one in connection with antigen-antibody reactions only. Choice III, the destruction of intracellular parasites, is discussed in paragraph three in connection with cell-mediated reactions only. Therefore, the answer is A: the two reactions have in common choice I only.


The best answer is B. This question requires you to recognize the structure of the passage as a whole. Paragraph one describes the way the antigen-antibody reaction works. Paragraph two discusses the difficulties with the antigen-antibody theory, which are, in this case, that the antigen-antibody theory cannot account for certain phenomena. Paragraph two also claims that accounting for these phenomena led scientists to the theory of cell-mediated reactions. Paragraph three describes the way the cell-mediated reaction works. The discussion is thus structured to support the theory of cell-mediated reactions by explaining how cell mediation accounts for phenomena not explained by the antigen-antibody theory.