RC Challenge -3

[abhasjha]

The survival of nerve cells, as well as their
performance of some specialized functions, is
regulated by chemicals known as neurotrophic
factors, which are produced in the bodies of animals,
(5) including humans. Rita Levi-Montalcini's discovery
in the 1950s of the first of these agents, a
hormonelike substance now known as NGF, was a
crucial development in the history of biochemistry,
which led to Levi-Montalcini sharing the "Nobel Prize
(10) for medicine in 1986.

In the mid-1940s, Levi-Montalcini had begun by
hypothesizing that many of the immature nerve cells
produced in the development of an organism are
normally programmed to die. In order to confirm this
(15) theory, she conducted research that in 1949 found
that, when embryos are in the process of forming
their nervous systems, they produce many more
nerve cells than are finally required, the number that
survives eventually adjusting itself to the volume of
(20) tissue to be supplied with nerves. A further phase of
the experimentation, which led to Levi-Montalcini's
identification of the substance that controls this
process, began with her observation that the
development of nerves in chick embryos could be
(25)stimulated by implanting a certain variety of mouse
tumor in the embryos. She theorized that a chemical
produced by the tumors was responsible for the
observed nerve growth. To investigate this hypothesis,
she used the then new technique of tissue culture, by
(30)which specific types of body cells can be made to
grow outside the organism from which they are
derived. Within twenty-four hours, her tissue cultures
of chick embryo extracts developed dense halos of
nerve tissue near the places in the culture where she
(35)had added the mouse tumor. Further research
identified a specific substance contributed by the
mouse tumors that was responsible for the effects
Levi-Montalcini had observed: a protein that she
named "nerve growth factor" (NGF).


(40) NGF was the first of many cell-growth factors to
be found in the bodies of animals. Through Levi-
Montalcini's work and other subsequent research, it
has been determined that this substance is present in
many tissues and biological fluids, and that it is
(45) especially concentrated in some organs. In developing
organisms, nerve cells apparently receive this growth
factor locally from the cells of muscles or other
organs to which they will form connections for
transmission of nerve impulses, and sometimes from
(50) supporting cells intermingled with the nerve tissue.
NGF seems to play two roles, serving initially to
direct the developing nerve processes toward the
correct specific "target" cells with which they must
connect, and later being necessary for the continued
(55)survival of those nerve cells. During some periods of
their development, the types of nerve cells that are
affected by NGF—primarily cells outside the brain
and spinal cord—die if the factor is not present or if
they encounter anti-NGF antibodies.


15. Which one of the following most accurately expresses
the main point of the passage?

(A) Levi-Montalcini's discovery of neurotrophic
factors as a result of research earned out in
the 1940s was a major contribution to our
understanding of the role of naturally occurring
chemicals, especially NGF, in the development
of chick embryos.

(B) Levi-Montalcini's discovery of NGF, a
neurotrophic factor that stimulates the
development of some types of nerve tissue
and whose presence or absence in surrounding
cells helps determine whether particular nerve
cells will survive, was a pivotal development in
biochemistry.

(C) NGF, which is necessary for the survival and
proper functioning of nerve cells, was
discovered by Levi-Montalcini in a series of
experiments using the technique of tissue
culture, which she devised in the 1940s.

(D) Partly as a result of Levi-Montalcini's research, it
has been found that NGF and other neurotrophic
factors are produced only by tissues to which
nerves are already connected and that the
presence of these factors is necessary for the
health and proper ftuictioning of nervous
systems.

(E) NGF, a chemical that was discovered by Levi-
Montalcini, directs the growth of nerve cells
toward the cells with which they must connect
and ensures the survival of those nerve cells
throughout the life of the organism except when
the organism produces anti-NGF antibodies.


16. Based on the passage, the author would be most likely
to believe that Levi-Montalcini's discovery of NGF is
noteworthy primarily because it

(A) paved the way for more specific knowledge of
the processes governing the development of the
nervous system

(B) demonstrated that a then new laboratory
technique could yield important and
unanticipated experimental results

(C) confirmed the hypothesis that many of a
developing organism's immature nerve cells are
normally programmed to die

(D) indicated that this substance stimulates
observable biochemical reactions in the tissues
of different species

(E) identified a specific substance, produced by
mouse tumors, that can be used to stimulate
nerve cell growth

17 The primary function of the third paragraph of the
passage in relation to the second paragraph is to

(A) indicate that conclusions referred to in the
second paragraph, though essentially correct,
require further verification

(B) indicate that conclusions referred to in the
second paragraph have been undermined by
subsequently obtained evidence

(C) indicate ways in which conclusions referred to
in the second paragraph have been further
corroborated and refined

(D) describe subsequent discoveries of substances
analogous to the substance discussed in the
second paragraph

(E) indicate that experimental procedures discussed
in the second paragraph have been supplanted
by more precise techniques described in the
third paragraph


18. Information in the passage most strongly supports
which one of the following?

(A) Nerve cells in excess of those that are needed
by the organism in which they develop
eventually produce anti-NGF antibodies to
suppress the effects of NGF.

(B) Nerve cells that grow in the absence of NGF are
less numerous than, but qualitatively identical
to, those that grow in the presence of NGF.

(C) Few of the nerve cells that connect with target
cells toward which NGF directs them are
needed by the organism in which they develop.

(D) Some of the nerve cells that grow in the
presence of NGF are eventually converted to
other types of living tissue by neurotrophic
factors.

(E) Some of the nerve cells that grow in an embryo
do not connect with any particular target cells.


19. The passage describes a specific experiment that tested
which one of the following hypotheses?

( A ) A certain kind of mouse tumor produces a
chemical that stimulates the growth of nerve
cells.

(B) Developing embryos initially grow many more
nerve cells than they will eventually require.

( C ) In addition to NGF, there are several other
important neurotrophic factors regulating cell
survival and function.

( D ) Certain organs contain NGF in concentrations
much higher than in the surrounding tissue.

(E) Certain nerve cells are supplied with NGF by
the muscle cells to which they are connected.


20. Which one of the following is most strongly supported
by the information in the passage?

(A) Some of the effects that the author describes as
occurring in Levi-Montalcini's culture of chick
embryo extract were due to neurotrophic factors
other than NGF.

(B) Although NGF was the first neurotrophic factor
to be identified, some other such factors are now
more thoroughly understood.
(C) In her research in the 1940s and 1950s, Levi-
Montalcini identified other neurotrophic factors
in addition to NGF.

(D) Some neurotrophic factors other than NGF
perform functions that are not specifically
identified in the passage.

(E) The effects of NGF that Levi-Montalcini noted
in her chick embryo experiment are also caused
by other neurotrophic factors not discussed in
the passage.

[abhasjha]

No takers for this passage . Anyways i am posting the official expalnation :


Question #15: The correct answer choice is (B)

with Main Point questions we should always try to prephrase an answer before looking at choices provided. In this case, the main point of this passage is to introduce the reader to the ' important scientific discovery of NGF, as well as the steps taken by the scientist in confirming early hypotheses, and further details about NGF uncovered through subsequent research.

Answer choice (A): The first half of this answer choice looks good, but the importance of the scientist's discovery was not to simply increase our understanding of chick embryos. Since the ramifications of Levi-Montalcini's discovery were further-reaching, this choice is wrong.

Answer choice (B): This is the correct answer choice. Most importantly, this response concludes that the discovery of NGF was pivotal to biochemistry, a fact reflected in the first paragraph.

Answer choice (C): This answer choice is relevant only to the second paragraph. Since the question asks for the main point of the passage, this answer should be eliminated. Furthermore, the passage states that Levi-Montalcini used the tissue-culture technique, not that she devised it.

Answer choice (D): This response confines its observations to the last paragraph, and does not reflect the main point of the passage. Furthermore, the passage actually stated that NGF is produced by tissues to which the nerve cells will connect, and this choice contrarily claims that NGF is produced
only when nerve cells have already connected.

Answer choice (E): Once again, this response should be immediately eliminated simply because it is relevant only to the last paragraph. Furthermore, this choice is false given the passage, because it leaves out the possibility that nerve cells die if NGF is simply removed.



Question #16: T h e correct answer choice is (A)

This question asks why the discovery of NGF is important, from thecperspective of the author. Since the author referenced the Nobel Prize and the importance this discovery to biochemistry in general, because an entire paragraph is dedicated to the discoveries that Levi-Montalcini's findings made
possible, we should look for an answer that underscores the significance of this contribution.

Answer choice (A): This is the correct answer choice. The last paragraph describes the more specific understanding that subsequent research led to, and the first paragraph describes the contribution to biochemistry as "crucial," and indicates that the contribution led to Levi-Montalcmi'', eventually winning the Nobel Prize.


Answer choice (B): Since Levi-Montalcini actually expected many of the results that she eventually observed, there is no support for the idea that the author believes anything about "unanticipated"results.

Answer choice (C): It seems that the discoveries in the last paragraph have been the most important from the author's perspective, rather than this particular confirmation. The author refers to the development as "crucial" to biochemistry, and it is advisable to look for a choice that explains the crucial nature of the development.

Answer choice (D): Levi-Montalcini's experiments did show observable reactions in the tissues of different species; however, the ultimate significance in these experiments lies in the fact that they lead to the expansion of knowledge of how the nervous system develops and functions.

Answer choice (E): The experiments did identify a substance, produced by mouse tumors, that stimulates nerve growth. However, that was not the ultimate finding of this important scientificdiscovery, so this choice is wrong.



Question #17: The correct answer choice is (C)

This question exemplifies the value of understanding passage organization. Again, the second paragraph describes the experiments, and the third paragraph describes subsequent developments, so the correct response should reflect such a relationship. In reviewing the answer choices, it is advisable to eliminate any response that is not aligned with this description, and verify or rule out the
remaining choices based on the information in the passage.

Answer choice (A): The third paragraph offers no indication that Levi-Montalcini's conclusions required further confirmation. In fact, the third paragraph deals with some of t he findings that are built on discoveries dealt with in the second paragraph.

Answer choice (B): In the third paragraph, the author discusses h ow science h a s built upon Levi- Montalcini's conclusions, which is rather contrary to the idea that science h a s undermined those conclusions.

Answer choice (C): This is the correct answer choice, as the third paragraph deals with further scientific developments based on discoveries discussed in the second paragraph.

Answer choice (D): In the third paragraph the author does not introduce any new, analogous substances, so this answer is incorrect.

Answer choice (E): Since the third paragraph discusses no experimental techniques, this response cannot be a description of its function.


Question #18: The correct answer choice is (E)

In approaching this Must Be True question, we should eliminate responses that are contrary to facts and inferences within the passage.

Answer choice (A): This answer choice states that nerve cells produce anti-NGF, and is therefore unsupported by the passage, which never indicates precisely where anti-NGF is produced.

Answer choice (B): This choice asserts that cells not affected by NGF are less numerous than those affected by NGF, and that the different cells have the same qualities. While me passage does support the idea that there are different types of cells, not all of which ate affected by NGF, no further detail is offered as to similarities or quantitative comparisons.

Answer choice (C): The passage does suggest that a significant number of nerve cells probably die off in the process of an organism's development. However, since the passage never offers any information about the relative number of surviving cells, the conclusion that "few" cells are needed is unsupported.

Answer choice (D): Nothing in the passage indicates that some nerve cells have the capacity to change into other types of living tissue, so this answer choice is incorrect.








Answer choice (E): This is the correct answer choice, as it is supported by the discussion in the second paragraph. The passage states that an embryo initially produces more nerve cells than needed and that the extra cells die off, which already supports the idea that the embryo produces nerve cells that do not end up connecting to anything. Furthermore, the second paragraph indicates that "NGF governs the process by which some nerve cells develop and others die off (lines 14-26), and the third paragraph explains, in detail, that NGF is the causal factor that helps direct nerve cells toward target cells. It is reasonable to conclude that since some nerve cells will die off, they do not receive "NG
and do not connect with target cells.



Question #19: The correct answer choice is (A)

There is only one specifically described experiment, and that is the one that tests Lewi-Montacini’shypothesis that a chemical produced by mouse tumors stimulated nerve growth.

Answer choice ( A ) : This is the correct answer choice. Lines 20-28 deal with Levi-Montalctni's hypothesis that a mouse tumor produces a chemical that stimulates nerve growth, and lines 28-39 provide a description of the experiment.

Answer choice ( B ) : This choice contains true information; in lines 14-20, the passage informs us that Lewi- Montalcini actually did test the hypothesis that many nerve cells are pre-programmed to die.
However, the passage does not describe that experiment, offering no details about the process of the experiment.

Answer choice ( C ) : The author indicates in the first paragraph that NGF is not the only neurotrophic factor. and mentions anti-NGF antibodies in the last paragraph; however, the author never provides the particulars of experiments that tested any such hypothesis or produced these results.

Answer choice ( D ) : The information in this answer choice may be true, given the fact that NGF is especially concentrated in some organs." However, the passage does not deal with organs' concentration relative to that of surrounding tissue. Further, this is not the hypothesis that the passage described the testing experiment for, so this answer choice is incorrect.




Answer choice (E): While this is apparently the case, given the information in the third paragraph, the passage never deals with any specific experiment that confirmed this hypothesis.



Question #20: The correct answer choice is (D)

Once again, for Must Be True questions, we should seek to eliminate all answer choices that are unconfirmed by, or clearly contrary to the information within the passage.
Answer choice (A): Since the author never discusses neurotrophic factors other than NGF, this response is unsupported.

Answer choice (B): This answer choice is only partially accurate, and therefore incorrect. It is true that NGF was the first neurotrophic factor to be identified, and that other such substances have since been found. However, the passage never offers any information about the relative degree to which these various factors are currently understood, so this answer is incorrect.

Answer choice (C): The passage only deals with the scientist's discovery of NGF. While there is discussion of other such factors, there is no reference to her having discovered them. This answer choice is thus unsupported and incorrect.

Answer choice (D): This is the correct answer choice. In the first paragraph, the author describes NGF as the first such agent discovered, and that neurotrophic factors regulate nerve cell survival as well as "some specialized functions." Since these further functions are not specified within the passage, and the role of NGF as discussed seems to be relevant only to growth and survival, the
assertion in this answer choice seems quite likely.


Answer choice (E): Since the experiments discussed in the passage only concern NGF with respect to nerve growth, there is no reason to assume that the observed effects were caused by other neutrorotrophic factors. Other factors certainly might have come into play, but we cannot assume that was the case .

[aj5105]

source of this RC? LSAT?

[cricketsteve5]

Hi,

It would be nice if you could let us all know from where you got these "Official Explanations".
Is there any site from which you can get explanations for these LSAT RCs.

Thanks for reading my post.


Regards,
Sairam