Reading ComprehensionDifficulty: Hard

PT117 S1 P3 Q18 Explanation

NGF

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TopicsInferenceScience

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Passage

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, including humans. Rita Levi-Montalcini’s discovery in the 1950s of the first of these agents, a hormonelike substance now known as NGF, was led to Levi-Montalcini sharing the Nobel Prize 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 theory, she conducted research that in 1949 found that, when embryos are in the process of forming their nervous systems, responsible for the effects Levi-Montalcini had observed: a protein that she named “nerve growth factor” (NGF).

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 especially concentrated in some organs. In developing organisms, nerve cells brain and spinal cord—die if the factor is not present or if they encounter anti-NGF antibodies.

What this question is testing

Inference

Your task

Find what must be true based on what the passage or stimulus states.

Common trap

Answers that are plausible or likely but not actually guaranteed by the text.

Winning move

Keep only the choice the statements fully support — eliminate anything that requires an extra assumption.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
18.

Information in the passage most strongly supports which one of

Answer choices

  1. Out of Scope: eventually produce7% picked this

    Nerve cells in excess of those that are needed by the organism in which they develop eventually produce anti-NGF antibodies to

    This answer is saying that the extra nerve cells made when an organism is developing later produce anti-NGF antibodies. We never heard anything like that. The passage never identifies any source of anti-NGF antibodies. It just says in the final sentence that the types of nerve cells that are affected by NGF can also be killed by anti-NGF antibodies.

  2. Too Strong: qualitatively identical5% picked this

    Nerve cells that grow in the absence of NGF are less numerous than, but qualitatively identical to, those that grow

    We don't know anything about nerve cells that grow in the absence of NGF. The final sentence of the passage implies that such cells may exist, because it allows for "types of nerve cells that aren't affected by NGF", but we don't know anything about them and so we certainly can't sign off on the extreme idea that they are qualitatively identical to nerve cells that are affected by NGF.

  3. Too Strong: Few10% picked this

    Few of the nerve cells that connect with target cells toward which NGF directs them are needed by the

    This answer says that most of the nerve cells that are directed by NGF to connect with target cells are not needed by the organism? Where would we get that most of NGF's work in patching nerve cells to target cells is useless, unneeded work?

  4. Out of Scope16% picked this

    Some of the nerve cells that grow in the presence of NGF are eventually converted to other types of

    Out of Scope: converted to other tissue The passage never talks about any nerve cells being converted into other types of living tissue.

  5. Correct62% picked this

    Some of the nerve cells that grow in an embryo do not connect with any

    Why this is right

    In the 2nd sentence of the 2nd paragraph, it says 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 tissue to be supplied with nerves. So if a body makes 1 million nerve cells but only 600,000 of them are required, then the other 400,000 die off. The 2nd to last sentence of the passage explains that "NGF serves to direct the developing nerve processes toward the correct, specific target cells with which they must connect". So by putting these two thoughts together, it sounds like we make 1 million nerve cells. The NGF helps attach all these wires to the tissues that need connection. Then there are extra nerve cells that die-off, because they weren't needed to connect with any particular target cells.

    Skill tested: Inference · how this choice captures the passage's function is the move to repeat next time.

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