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# The antigen-antibody immunological reaction used to be regarded as

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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
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gmatprep09
Hi,

What do you guys think of this passage. I found this pretty confusing. Is there a strategy to tackle these kind of passages and questions? If possible, can you include your reasoning for each question? Thanks

1. E; 2. E; 3. D; 4. C; 5. A; 6. B; 7. A; 8. B.
1 E 04:36 correct
2 E 02:56 correct
3 B 01:14 incorrect
4 A 00:27 incorrect
5 A 00:17 correct
6 d 02:57 incorrect
7 e 00:30 incorrect
8 D 04:18 incorrect

what a heartbreaker it is ....
on a serious note if i look back the passage and read the answer options again , I could have got 4 , 7,8 correct ..need to learn to stay focussed in passages like these...but a toughie..i it comes in exam it will take away lot of time ....for sure..
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
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gmatprep09
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. 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. 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

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. 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. 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. 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. 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. 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

Eye opening biology passage...still answers were somewhat predictable..kudos for sharing
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
Both the passage and the questions were at par in terms of difficulty.
Amazingly drafted questions and options.
2 incorrect, 15 mins.
I guess it's official question.
Request a moderator to modify the difficulty tag from Sub600 level to 700 level. Thanks!
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
Hey,

One way to manage time and read passages effectively is to read what is important and what is not because you can solve 80% of the passage by reading 20% of the passage.

All the very best.

Thanks,
Saikiran
Byju's GMAT Expert
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
Q1: 5:53 Correct
Q2: 1:48 correct
Q3: 0:56 incorrect
Q4: 1:30 correct
Q5: 2:30 correct
Q6: 0:30 correct
Q7: 0:29 incorrect
Q8: 02:23 correct

Took a while to understand the structure.
My problem is if I do passages in person ( as in not part of a test) I am able to understand the structure and answer well.
However on mocks, I suffer from mental blockage of time constraint.

I genuinely feel I am running out of time while on test.
Can someone help me what should I do in such scenario?

I usually see how stupidly I mark answers to questions while on Mocks but while on customized quizzes or GMAT club timer,
I have a higher score for the same question ( I bet :P )

Regards,
Rishav
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
Hello Moderators and Experts GMATNinja sir, VeritasKarishma Ma'am,
Could you please help me whether the line of my reasoning is correct regarding Question no. 8:
It's pretty evident from the passage that option B is the answer, based on these lines:
Quote:
When molecular biologists discovered, more-
over, that such information cannot flow from
protein to protein, but only from nucleic acid to
protein, the theory that an antigen itself pro-
vided the mold that directed the synthesis of an
antibody had to be seriously qualified.

Regarding option A, the assumption is that
Antigen ( a foreign substance) attacks lymphocyte cells to produce antigens
But the cell-mediation process does not question this. It only explains how antigens react with Lymphocytes with new perspective.

This is the reason why option A is wrong.

Am I correct with my reasoning?

Regards,
Rishav
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
rish2708
Hello Moderators and Experts GMATNinja sir, VeritasKarishma Ma'am,
Could you please help me whether the line of my reasoning is correct regarding Question no. 8:
It's pretty evident from the passage that option B is the answer, based on these lines:
Quote:
When molecular biologists discovered, more-
over, that such information cannot flow from
protein to protein, but only from nucleic acid to
protein, the theory that an antigen itself pro-
vided the mold that directed the synthesis of an
antibody had to be seriously qualified.

Regarding option A, the assumption is that
Antigen ( a foreign substance) attacks lymphocyte cells to produce antigens
But the cell-mediation process does not question this. It only explains how antigens react with Lymphocytes with new perspective.

This is the reason why option A is wrong.

Am I correct with my reasoning?

Regards,
Rishav

Quote:
8. The author supports the theory of cell-mediated reactions primarily by
Quote:
When molecular biologists discovered, more-over, 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.

It means that there is something more lacking in the explanation. This explanation can be completed by cell-mediated immunity

In 1st theory:
Lymphocytes form antibodies when antigen come in contact with lymphocytes. Lysis rupture antigenic cells and then macrophages& polymorphs engulf these antigents’ contents.

Unexplanied: antibodies and antigens can not directly interact ( protein and protein)
Missing item: Cell-mediated immunity immunological response.
Explanation: In this response, receptors sites on lymphocytes and surface antigens form binds ( nucleus-protein)

Quote:
(A) pointing out a contradiction in the assumption leading to the antigen-antibody theory
There is no contradiction as such

Quote:
Regarding option A, the assumption is that
Antigen ( a foreign substance) attacks lymphocyte cells to produce antigens
But the cell-mediation process does not question this. It only explains how antigens react with Lymphocytes with new perspective.

I think you mean, Antigen ( a foreign substance) attacks lymphocyte cells to produce “antibodies”.

Their assumption is NOT WRONG, As per antigen-antibody theory , they analyze the process that Antigen ( a foreign substance) attacks lymphocyte cells to produce “antibodies”.( This is not a WRONG ASSUMPTION but IT IS INCOMPLETE ). On further analysis they realize they need to evaluate further and thus found Protein –Protein can not interact directly and then came up with NEW EXPLANATION how antigens are destroyed.( without creating antibodies)
So during explanation, they assume as per given parameters but later found they have missed some basic concepts and thus reevaluated and made new explanation.

Hope it is clear.
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
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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.
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
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17 minutes and 10 seconds (average of 2 minutes and 8 seconds per questions). 8/8 correct. I think that I would have taken far less if I had read more carefully and taken a few notes in the first try. For hard passages such as this one, which contain dense information, making a mental map and taking very brief notes is important

Hopefully it's useful for you all!
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
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
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
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sv2023
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

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.
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The antigen-antibody immunological reaction used to be regarded as [#permalink]
RonTargetTestPrep
sv2023
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

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.

Hi RonTargetTestPrep thankyou so much for writing back, its now clear to me why option A is wrong. I noticed you wrote that the antigen antibody theory has no assumptions provided, rather you've called them principles. Can I ask what is your reasoning to use the specific word "principles" and not "assumptions"?
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
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)
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
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Rickooreo
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)

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.
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Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
Hello, could anyone explain why C in answer 8 is not correct? Thank you!! Nikhil

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

(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

I was hesitating between B & C , but for me C made sense because of the following:

"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"

==> this demonstrate that scientist were reluctant to abandon the hypothesis and ignore some difficulties

"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. "

==> this demonstrate show new data that came to explain a process they ignored and revealed something else.
Re: The antigen-antibody immunological reaction used to be regarded as [#permalink]
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