The antigen-antibody immunological reaction used to be regarded as

Question

The antigen-antibody immunological reaction used to be regarded as typical of immunological responses. Antibodies are proteins synthesized by specialized cells called plasma cells, which are formed by lymphocytes (cells from the lymph system) when an antigen, a substance foreign to the organism’s body, comes in contact with lymphocytes. Two important manifestations of antigen-antibody immunity are lysis, the rapid physical rupture of antigenic cells and the liberation of their contents into the surrounding medium, and phagocytosis, a process in which antigenic particles are engulfed by and very often digested by macrophages and polymorphs. The process of lysis is executed by a complex and unstable blood constituent known as complement, which will not work unless it is activated by a specific antibody; the process of phagocytosis is greatly facilitated when the particles to be engulfed are coated by a specific antibody directed against them.

The reluctance to—abandon this hypothesis, however well it explains specific processes, impeded new research, and for many years antigens and antibodies dominated the thoughts of immunologists so completely that those immunologists overlooked certain difficulties. 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 a 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 and some of which stimulate increased phagocytic activity by white blood cells of the macrophage type. Cell-mediated immunity also accounts for the destruction of intracellular parasites.   1 
 1. The author is primarily concerned with

(A) proving that immunological reactions do not involve antibodies
(B) establishing that most immunological reactions involve antigens
(C) criticizing scientists who will not change their theories regarding immunology
(D) analyzing the importance of cells in fighting disease
(E) explaining two different kinds of immunological reactions

2 
 2. The author argues that the antigen-antibody explanation of immunity “had to seriously qualified” ( Highlighted ) because

(A) antibodies were found to activate unstable components in the blood
(B) antigens are not exactly complementary to antibodies
(C) lymphocytes have the ability to bind to the surface of antigens
(D) antibodies are synthesized from protein whereas antigens are made from nucleic acid
(E) antigens have no apparent mechanism to direct the formation of an antibody

3 
 3. The author most probably believes that the antigen-antibody theory of immunological reaction.

(A) is wrong
(B) was accepted without evidence
(C) is unverifiable
(D) is a partial explanation
(E) has been a divisive issue among scientists

4 
 4. The author mentions all of the following as being involved in antigen-antibody immunological reactions EXCEPT the

(A) synthesis of a protein
(B) activation of complement in the bloodstream
(C) destruction of antibodies
(D) entrapment of antigens by macrophages
(E) formation of a substance with a structure complementary to that of an antigen

5 
 5. The passage contains information that would answer which of the following questions about cell-mediated immunological reactions?

I. Do lymphocytes form antibodies during cell-mediated immunological reactions?
II. Why are lymphocytes more hostile to antigens during cell-mediated immunological reactions than are other cell groups?
III. Are cell-mediated reactions more pronounced after transplants than they are after parasites have invaded the organism?

(A) I only
(B) I and II only
(C) I and III only
(D) II and III only
(E) I, II, and III

6 
 6. The passage suggests that scientists might not have developed the theory of cell-mediated immunological reactions if

(A) proteins existed in specific group types
(B) proteins could have been shown to direct the synthesis of other proteins
(C) antigens were always destroyed by proteins
(D) antibodies were composed only of protein
(E) antibodies were the body’s primary means of resisting disease

7 
 7. According to the passage, antibody-antigen and cell-mediated immunological reactions both involve which of the following processes?

I. The destruction of antigens
II. The creation of antibodies
III. The destruction of intracellular parasites

(A) I only
(B) II only
(C) III only
(D) I and II only
(E) II and III only

8 
 8. The author supports the theory of cell-mediated reactions primarily by

(A) pointing out a contradiction in the assumption leading to the antigen-antibody theory
(B) explaining how cell mediation accounts for phenomena that the antigen-antibody theory cannot account for
(C) revealing new data that scientists arguing for the antigen-antibody theory have continued to ignore
(D) showing that the antigen-antibody theory fails to account for the breakup of antigens
(E) demonstrating that cell mediation explains lysis and phagocytosis more fully than the antigen-antibody theory does

Nikhil · Accepted Answer

1. The author is primarily concerned with

(A) proving that immunological reactions do not involve antibodies
(B) establishing that most immunological reactions involve antigens
(C) criticizing scientists who will not change their theories regarding immunology
(D) analyzing the importance of cells in fighting disease
 (E) explaining two different kinds of immunological reactions

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).

2. The author argues that the antigen-antibody explanation of immunity “had to seriously qualified” (line 37) because

(A) antibodies were found to activate unstable components in the blood
(B) antigens are not exactly complementary to antibodies
(C) lymphocytes have the ability to bind to the surface of antigens
(D) antibodies are synthesized from protein whereas antigens are made from nucleic acid
 (E) antigens have no apparent mechanism to direct the formation of an antibody

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.

3. The author most probably believes that the antigen-antibody theory of immunological reaction.

(A) is wrong
(B) was accepted without evidence
(C) is unverifiable
 (D) is a partial explanation 
(E) has been a divisive issue among scientists

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."

4. The author mentions all of the following as being involved in antigen-antibody immunological reactions EXCEPT the

(A) synthesis of a protein
(B) activation of complement in the bloodstream
 (C) destruction of antibodies 
(D) entrapment of antigens by macrophages
(E) formation of a substance with a structure complementary to that of an antigen

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.

5. The passage contains information that would answer which of the following questions about cell-mediated immunological reactions?

I. Do lymphocytes form antibodies during cell-mediated immunological reactions?
II. Why are lymphocytes more hostile to antigens during cell-mediated immunological reactions than are other cell groups?
III. Are cell-mediated reactions more pronounced after transplants than they are after parasites have invaded the organism? 
 (A) I only 
(B) I and II only
(C) I and III only
(D) II and III only
(E) I, II, and III

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.

6. The passage suggests that scientists might not have developed the theory of cell-mediated immunological reactions if

(A) proteins existed in specific group types
 (B) proteins could have been shown to direct the synthesis of other proteins 
(C) antigens were always destroyed by proteins
(D) antibodies were composed only of protein
(E) antibodies were the body’s primary means of resisting disease

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.

7. According to the passage, antibody-antigen and cell-mediated immunological reactions both involve which of the following processes?

I. The destruction of antigens
II. The creation of antibodies
III. The destruction of intracellular parasites 
 (A) I only 
(B) II only
(C) III only
(D) I and II only
(E) II and III only

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.

8. The author supports the theory of cell-mediated reactions primarily by

(A) pointing out a contradiction in the assumption leading to the antigen-antibody theory
 (B) explaining how cell mediation accounts for phenomena that the antigen-antibody theory cannot account for 
(C) revealing new data that scientists arguing for the antigen-antibody theory have continued to ignore
(D) showing that the antigen-antibody theory fails to account for the breakup of antigens
(E) demonstrating that cell mediation explains lysis and phagocytosis more fully than the antigen-antibody theory does

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.

thangvietname · Answer

we read, if we focus on purpose of the details , we can realize the big idea in each paragraph and the main idea of the passage easily. we focus on details themself only when we are asked a specific questions.

focus on purpose of the details is key to understanding the passage quickly.

each of paragraph in this passage is long and full of details. but it is easy to realize the purpose of the details and the big idea in each paragraph.

a reading skill is important. the skill is we have to realize the purpose of the details when we read the details. this can be done with practice. this can be accomplished when you quickly realize the grammatical role of each phrase and of tense of verbs.

so, you need to read a lot but remember, when you read,you have to realize grammatical role of each phrase and grammatical role of tense. you must be able to confirm the grammar points in grammar books with the text you are reading. this is called by someone in this forum " see grammar in action". only by doing this way, you can remember and master the grammar point.

for example, when you read the text and you see present tense you have to realize that which role this present tense play,. this present tense show a habit, a condition, a timeless fact which is alway right, or a condition which exist indefinitely. all of cases of use of present tense are in the grammar book already. what you have to do is to confirm the cases. in doing so, you master grammar point.

ashmhjn · Answer

Breakdown of the Passage -

P1.
Ag-Ab Process- 'used to be' regarded as a typical immunological response (direct hint that something is coming up to explain the 'used to' bit)
Let's move on.

Process - (This process is written in reverse, try to map it down directly from the passage and then read this from Right to Left)
Ab <- protein synth <- Plas cells <- contacts lymphocytes <- Ag

Then 2 manifestations (of Ag-Ab process)
1. lysis + process
2. phagocytosis + process

Basic idea behind the process -

Ag - contacts lymphocytes - plas cells - protein synth - Ab (already discussed above)

These antibodies then intiate -
1. Lysis - specific antibody > blood complement > ruptures antigen > liberates some content > engulfs/digests broken antigen
2. Phagocytosis - specific antibody > coats antigen > engulfs it

HINT - covid-19 has really simplified the understanding of Ag (substance that triggers an immune response) and Ab (what is then produced to fight the infection)

P2.
- Scientists felt this was a good enough explanation
- Reluctant to abandon this Ag-Ab process for years
- hurdled new research
- even overlooked difficulties

There's a reason this process 'used to be' a typical one. Now it's not. Let's explore the difficulties!

Difficulties of Ag-Ab process -
1. How is Ag recognized?
2. How is the blood complement synthesised?
3. Info cant flow Pr to Pr
4. Info can only flow NA to Pr

So must be another step where Ag is providing a hint to trigger that specific antibody to initiate Lysis or Phagocytosis.

Therefore, a second immunological reaction is mediated when Ag comes in contact with Lymphocytes - CELL-MEDIATED IMMUNITY

P3.
How has the understanding of CMI helped improve applications and other problems in the industry?

-improving/ new vaccines
-problems with transplants (why/how the receiver tries to kill foreign/donor tissue, organs)
- intracellular parasites

Big Picture -
P1 - Ag-Ab process, 2 mode of action, processes
P2 - Scientists thought it was great. But there are some unexplained factors. Ag-Ab Process is partial. Theres CMI Process also.
P3 - Understanding of CMI Process - improve/new industrial application.

yipmewmew · Answer

Can an expert please weigh in on why in Q8- option A is incorrect? Isnt the author refuting the assumption of the antigen antibody theory by saying that the exact complement cant be made? This option has really confused me. Kindly help

RonTargetTestPrep · Answer

Choice A says that there's "a contradiction   in   the assumption leading to the antigen-antibody theory".
"A contradiction IN this assumption" means that the assumption in question is  self- contradictory—a situation that would invalidate the entire theory that's based on that assumption.

This is incorrect in two different ways.

First, at no point does the passage describe the antigen/antibody theory as internally inconsistent (= self-contradictory). The problems with this theory came from  new findings  that contradicted its core tenets.

Second, nowhere does the passage mention any "assumption" of the theory. It describes only the principles of the theory itself, one of which is contradicted by the later findings.

Rickooreo · Answer

KarishmaB

Being from non-science background, it was difficult for me to comprehend the above passage, can you please suggest me an approach to attack such RC if they appear in exam (maybe length will be smaller, however the passage remains complex for me)

KarishmaB · Answer

Yes, that's understandable. Many science graduates struggle in business and arts passages. So know that it is a level playing field for all. That said, work on improving your understanding of science passages by subscribing to a science journal and reading its articles religiously!

Nothing more than that would be required by a GMAT passage.

VerbalBot · Answer

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The antigen-antibody immunological reaction used to be regarded as

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The antigen-antibody immunological reaction used to be regarded as

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