NGF

Answer choices

1. A

   Correct64% picked this

   paved the way for more specific knowledge of the processes governing the development of

   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%
2. B

   Wrong Emphasis: tissue culture2% picked this

   demonstrated that a then new laboratory technique could yield important and

   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%
3. C

   Wrong Emphasis: programmed to die8% picked this

   confirmed the hypothesis that many of a developing organism’s immature nerve cells are normally

   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%
4. D

   Wrong Emphasis: observable reactions9% picked this

   indicated that this substance stimulates observable biochemical reactions in the tissues

   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%
5. E

   Too Narrow: just NGF17% picked this

   identified a specific substance, produced by mouse tumors, that can be used to stimulate

   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%