RC Select Many GRE Sample Questions 6

GRE RC Select Many Sample Questions

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RC Passage

Perhaps the primary difficulty with the antigen-antibody explanation is the informational problem of how an antigen is recognized and how a structure exactly complementary to it is then synthesized. When molecular biologists discovered, moreover, that such information cannot flow from protein to protein, but only from nucleic acid to protein, the theory that an antigen itself provided the mold that directed the synthesis of an antibody had to be seriously qualified. The attempts at qualification and the information provided by research in molecular biology led scientists to realize that a second immunological reaction is mediated through the lymphocytes that are hostile to and bring about the destruction of the antigen. This type of immunological response is called cell-mediated immunity. Recent research in cell-mediated immunity has been concerned not only with the development of new and better vaccines, but also with the problem of transplanting tissues and organs from one organism to another, for although circulating antibodies play part in the rejection of transplanted tissues, the primary role is played by cell-mediated reactions. During cell-mediated responses, receptor sites on specific lymphocytes and surface antigens on the foreign tissue cells form a complex that binds the lymphocytes to the tissue. Such lymphocytes do not give rise to antibody-producing plasma cells but themselves bring about the death of the foreign-tissue cells, probably by secreting a variety of substances, some of which are toxic to the tissue cells.

Directions: Consider each of the choices separately and select all that apply.

1. Which of the following explains the reason for transplanted organs being rejected by the host body?

  • A. an immunological reaction triggered by the presence of antigens
  • B. actions carried out by antibodies
  • C. an immunological reaction brought about by lymphocytes
  • D. actions carried out by anti-body producing plasma cells
  • E. the binding of lymphocytes to foreign tissue cells
Answer

The correct answers are A, B, C and E.

Information presented in the passage discusses the reasons behind the rejection of transplanted tissues by the body of the host. It has been clearly brought out that cell-mediated reactions and antibodies are responsible for the rejection of the implanted organs and tissues. Cell-mediated reactions and antibodies are an after effect of the presence of antigens. Lymphocytes play an active role in the destruction of antigens. Towards the end of the passage the author has clearly brought out how lymphocytes attach themselves to the foreign tissue and destroy it. Therefore, A, B, C and E are all valid reasons for the rejection of the transplanted organs by the host body and hence, they all are correct answer options to the question asked. Antibody producing plasma cells do not affect the transplanted tissue in any way whatsoever and hence, D is incorrect.

2. According to the author, scientists are trying to find an answer to which of the following questions?

  • A. How is a structure complementary to an antigen synthesised?
  • B. Does an antigen provide the mold for the synthesis of an antibody?
  • C. Can cell-mediated responses be used for developing vaccines?
  • D. How is the immunological reaction mediated by the lymphocytes carried out?
  • E. How is an antigen recognised?
Answer

The correct answers are A and E.

The question whether an antigen provides the mold for the antibody has been addressed and the scientists have found that there is a second immunological reaction that is mediated through the lymphocytes. Therefore, B is incorrect. The author does not specify whether the usage of cell-mediated reactions for developing vaccines is still being explored or whether that potential has already been tapped. This does not mean that scientists are still looking for an answer to the question mentioned at C. Therefore, C is incorrect. The end of the passage clearly brings out the process by which the immunological reaction is mediated by the lymphocytes. Therefore, D is also incorrect. The passage begins with the note that it is still not clear how a structure complementary to the antigen is synthesised and the entire passage then deals with the results thrown up as an outcome of the research being carried out. This implies that A and E are the correct answers.

3. Which of the following is a valid conclusion based on the information provided in the passage?

  • A. Immunological reactions have nothing to do with rejection of transplanted organs by the host body
  • B. There are two types of lymphocytes
  • C. Lymphocytes are responsible for the annihilation of antigens
  • D. Antigens have nothing to do with the synthesis of antibodies
  • E. The presence of antigens does not affect the acceptance of transplanted organs by the host body
Answer

The correct answers are B and C.

The author has clearly brought out that cell-mediated reactions and antibodies are responsible for the rejection of the transplanted organs and tissues. It has been indicated that cell-mediated reactions, immunological reactions and antibodies are a result of the presence of antigens. Therefore, A and E are incorrect. The contents of the passage indicate that there is a specific type of lymphocytes that bind themselves to the foreign tissue. This implies that there are two types of lymphocytes and hence, B is correct. C is correct as implied by the contents of the passage. D is clearly incorrect as it has been brought out in the beginning that the structure of antibodies is complementary to that of the antigens and they are synthesised as a result of the presence of antigens. Therefore, B and C are the correct answers.

4. Which of the following processes is being described by “During cell-mediated responses, receptor sites on specific lymphocytes and surface antigens on the foreign tissue cells form a complex that binds the lymphocytes to the tissue”?

  • A. Rejection of an implanted organ by the host organism
  • B. Antigen-antibody hypothesis
  • C. Role of lymphocytes during cell-mediated responses
  • D. Role of antigens
  • E. Structure of foreign tissue cells
Answer

The correct answers are A and C.

The sentence in question does not discuss anything in reference to the antibody-antigen hypothesis; rather it is describing the role that is played by lymphocytes during cell-mediated responses that result in the rejection of a transplanted organ by the host tissue. In view of the above, it is evident that B, D and E are incorrect and A and C are the correct answers.

5. Which of the following have been used to describe cell-mediated immunity?

  • A. “information provided by research in molecular biology”
  • B. “lymphocytes that are hostile to and bring about the destruction of the antigen”
  • C. “a second immunological reaction”
  • D. “immunological response”
  • E. “informational problem of how an antigen is recognized”
Answer

The correct answers are B, C and D.

Cell-mediated immunity has been described by the author by stating that a second immunological reaction is mediated through the lymphocytes that are hostile to and bring about the destruction of the antigen. It has also been brought out that this type of immunological response is referred to as cell-mediated immunity. In view of the above it is evident that A and E are clearly incorrect and B, C and D correctly describe cell-mediated immunity as intended by the author and therefore, B, C and D are the correct answers.

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