The Survival of Nerve Cells, As Well As their Performance of Some Specialized Functions

Reading Passage Question:

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.

“The survival of nerve cells, as well as their performance of some specialized functions” - this is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.

This GMAT Reading Comprehension consists of 4 comprehension questions. The GMAT Reading Comprehension questions are designed for testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.

Solution and Explanation

1. 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 carried 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 functioning of nervous systems.
(E) NGF, a chemical that was discovered by LeviMontalcini, 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.

2. 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

3. 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

4. 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.

5. 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.

6. 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, LeviMontalcini 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.

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