Reading Comprehension

PT117 · S1 · P3 · Q16 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.

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

  1. Correct

    paved the way for more

    Why this is right

    This isn't super tempting on a first pass, but "paved the way" matches up well with "a crucial development" (in the 1st), and with "Through her work and other subsequent research, it has been determined" (in the 3rd). Before Levi-Montalcini, we didn't even know there was such a thing as cell-growth factors or neurotrophic factors. She hypothesized that a developing nervous system produces many more nerve cells than are finally required and the "keepers" are the ones that end up in tissue supplied with nerves. In the 3rd paragraph, we hear that her research on NGF helped us understand how neurotrophic chemicals direct the developing nerve processes toward the correct target cells.

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

    64% picked this

  2. demonstrated that a then new

    Wrong Emphasis: tissue culture

    This answer is making it seem like Rita's main contribution was using the new technique of tissue culture, but that is not why she is being spotlighted in this passage. Her discovery of NGF is definitely the more central accomplishment.

    2% picked this

  3. confirmed the hypothesis that many

    Wrong Emphasis: programmed to die

    The passage doesn't make it sound like prior to Rita's work, there was some hypothesis circling through the scientific community that many immature nerve cells are programed to die, and then she came along and confirmed it. The second paragraph says that her research began with her hypothesis that many immature nerve cells are programmed to die. And her confirmation of this fact is not the main event. As she was conducting research trying to confirm this hypothesis of hers, she accidentally stumbled on NGF, and that discovery revolutionized biochemistry.

    8% picked this

  4. indicated that this substance stimulates

    Wrong Emphasis: observable reactions

    This is a very vague idea ... many, many substances (for example, Vitamin C, nicotine, ibuprofen) will stimulate observable biochemical reactions in the tissues of different species. So, sure, NGF will also do so, but that's far too generic of a "discovery".

    9% picked this

  5. identified a specific substance, produced

    Too Narrow: just NGF

    This answer describes what's going on in the 2nd paragraph, where Rita is doing her specific research on chick embryos and mouse tumors. She does identify a specific substance responsible for the nerve cell growth, the protein she names NGF. But the primary significance of Rita's work is where the field of biochemistry goes from there. Once she makes them aware of such things as neurotrophic / cell-growth factors, they start to learn more about how these chemicals influence the development and operation of the nervous system.

    17% picked this

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