Reading Comprehension

PT117 · S1 · P3 · Q15 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.

15.

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

Levi-Montalcini’s discovery of neurotrophic factors
Wrong Emphasis: chick embryos
This answer feels very close, because the main clause is saying, "Her discovery was a major contribution to our understanding". But she is noteworthy for how she contributed to our understanding of neurotrophic factors and other cell-growth factors, not to our understanding of "natural chemicals in the development of chick embryos". Her work on chick embryos led her to discover NGF, and NGF was mind-blowing on a much broader scale to the field of biochemistry. It wasn't because of what it was specifically saying about chick embryos (these neurotrophic factors she opened our eyes to occur in all animals, including humans).
3% picked this
Correct
Levi-Montalcini’s discovery of NGF, a
Why this is right
This main clause better matches the end of the 1st sentence, where the author is putting a stamp on why Levi-Montalcini is noteworthy: Her discovery of NGF was a pivotal development in biochemistry. This answer choice has so much fluff in between the Subject and the Verb of the main clause, it's a really good example of why we practice initially just reading the main clause on Main Point answers. Once we feel good about the main clause, we have to sign off on all the details. Is NGF a neurotrophic factor that stimulates the development of some types of nerve tissue? Yes. She found that she could stimulate the development of nerves in chick embryos by implanting tumors that contained NGF. Is NGF something whose presence or absence in surrounding cells helps determine whether nerve cells will survive? Yes, "NGF seems to play two roles -- serving initially to direct the developing nerve processes toward the correct target cells, and later being necessary for the continued survival of those cells".
Skill tested: Main Point · how this choice captures the passage's function is the move to repeat next time.
82% picked this
NGF, which is necessary for
Too Narrow
This is somewhat tempting, but it just tells us the small story about what Levi-Montalcini did, without giving us the larger importance or ramification of that story. The main clause is, NGF was discovered by Levi-Montalcini in a series of experiments using tissue culture. Okay, that seems true. But why is that important? The passage is talking about her discovery of NGF because it opened up the world of biochemistry's eyes to this whole class of chemicals similar to NGF called neurotrophic factors (or cell-growth factors).
9% picked this
Partly as a result of
Too Strong
Too Strong: only Wrong Emphasis: what produces NGF The main clause here is, it's been found that NGF and other neurotrophic factors are produced only by tissues to which nerves are already connected, and these factors need to be present for the health and proper functioning of nervous systems. Levi-Montalcini doesn't appear in the main clause, despite her seeming like a very central part of the passage, not just a throwaway intro "partly as a result of her research". It seems like the restrictive claim that NGF is produced only by tissues is contradicted in the 3rd paragraph, where it says, "It has been determined that [NGF] is present in many tissues and biological fluids, and that is especially concentrated in some organs".
1% picked this
NGF, a chemical that was
Too Narrow Too Strong: ensures
This is another answer that puts Levi-Montalcini in the background. And it centers on the specific things we learned about NGF, without capturing the idea that discovering NGF open our eyes to a whole new class of agents like it. There is definitely no reason that anti-NGF antibodies should be making any appearance in our main point answer. They were brought up only in the final sentence as a very inconsequential detail. A lot of Main Point questions have a trap answer that overvalues the last thing students heard in the passage. Finally, this says that NGF "ensures the survival of cells" where the passage just said that it is necessary to the continued survival of cells.
5% picked this

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