Reading Comprehension

PT117 · S1 · P3 · Q18 NGF

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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.

Topic

The discovery and role of nerve growth factor (NGF) and neurotrophic factors in nerve cell survival and development.

Framework

Highlight Noteworthy (with a touch of Answer / Explain—explaining how NGF works and why it's important)

Main Point

Rita Levi-Montalcini’s discovery of nerve growth factor (NGF) was a landmark achievement that explained how nerve cells survive, develop, and connect, revealing the key role of neurotrophic factors in animal biology. (The Most Valuable Sentence: The first paragraph’s closing sentence: )

P1: Introduction to Neurotrophic Factors and Levi-Montalcini’s Discovery

We’re introduced to neurotrophic factors—special chemicals that help nerve cells survive and work. Rita Levi-Montalcini discovered the first important one (NGF), which forever changed how scientists thought about nerve cells and earned her a Nobel Prize.

P2: The Experiments and Discovery of NGF

Levi-Montalcini thought lots of nerve cells were meant to die off during development, and she found evidence for this in embryos. Noticing that mouse tumors caused unusual nerve growth in chick embryos, she guessed a chemical from the tumors was responsible. By using tissue cultures, she proved that a specific protein produced by the tumors—NGF—was making this happen.

P3: The Function and Importance of NGF

NGF turned out to be the first of many such growth factors in animals. Thanks to Levi-Montalcini’s work and later research, scientists now know NGF helps nerve cells not just grow, but also survive and connect to the right targets during development. If nerve cells don’t get NGF, they can’t survive, which makes this protein crucial for healthy nervous systems, especially outside the brain and spinal cord.

18.

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

  1. Nerve cells in excess of

    Out of Scope: eventually produce

    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.

    7% picked this

  2. Nerve cells that grow in

    Too Strong: qualitatively identical

    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.

    6% picked this

  3. Few of the nerve cells

    Too Strong: Few

    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?

    10% picked this

  4. Some of the nerve cells

    Out of Scope

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

    15% picked this

  5. Correct

    Some of the nerve cells

    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.

    62% picked this

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