NGF

Answer choices

1. A

   Wrong Emphasis: chick embryos3% picked this

   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

   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%
2. B

   Correct82% picked this

   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

   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%
3. C

   Too Narrow9% picked this

   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

   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%
4. D

   Too Strong1% picked this

   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

   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%
5. E

   Too Narrow Too Strong: ensures5% picked this

   NGF, a chemical that was discovered by Levi-Montalcini, directs the growth of nerve cells toward the cells with which they must connect and 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%