#21 - Global Reference, Must Be True

[Administrator]

Complete Question Explanation

The correct answer choice is (D).

Answer choice (A):

Answer choice (B):

Answer choice (C):

Answer choice (D): This is the correct answer choice.

Answer choice (E):


This explanation is still in progress. Please post any questions below!

[elliottsdavis]

I was down to answers D and E - eliminating A, B, and C - though I could not find support in the text for either one. What does the passage say that supports silicon, gallium arsenide, and lithium phosphide to not be the only semiconductor materials to which peptides have been found to bind? The closest support I could find was "they have expanded their targets to 20 more semiconductor materials," but this seems to suggest only that the researchers were TESTING whether any other semiconductor material can bind with peptides, not that they have FOUND this to be the case. Thanks in advance for the help!

[Jeremy Press]

Hi Elliott,

Very good eye here, on a pretty difficult "Most Strongly Supported" question. You were right to eliminate A, B, and C, and you should feel comfortable eliminating answer choice E as well, because there is simply nothing in the passage to back up the notion that peptides have been used in non-semiconductor industrial applications (the passage focuses solely on the use of peptides in relation to semiconductors).

Extend the line you looked at just a tad further! It says, "As they have expanded their targets to 20 more semiconductor materials, their cache of crystal-manipulating peptides has ballooned into the hundreds." This suggests they've found new peptides that bind to some of those 20 additional semiconductor materials. After all, how else would their stock of "crystal-manipulating peptides" have ballooned? Is it a perfect, 100% valid inference? Not in the Must Be True sense, no. But is it "most strongly supported" by the passage, when compared against A, B, C, and E? Absolutely.

I hope this helps!

Jeremy

[mkarimi73]

Ok, I understand the "process of elimination" technique for Most Strongly Supported inference questions. But I have to take issue with the wording of (D). It says, "Silicon, gallium arsenide, and indium phosphide are not the only semiconductor materials to which peptides have been found to bind," meaning in addition to those 3 semiconductor crystals, they have found even more peptides that bind. The later half of (D) is supported; the first part isn't.

In the second paragraph, the second-to-last sentence states: "They found a few peptides that not only bound exclusively to one of the crystals in the experiment but also latched onto a particular face of the crystal." There is no indication here that all 3 crystals were found to bind to the peptides Belcher/Hu tested. Am I missing something here? Thanks in advance.

[Luke Haqq]

Hi mkarimi73!

That there are other semiconductor materials comes across in the final paragraph.

In particular, it states: "to use such a method to assemble a set of circuit-building tools it would be necessary to identify many additional organic compounds that bind to circuit-component materials. The group is making progress on that quest. As they have expanded their targets to 20 more semiconductor materials, their cache of crystal-manipulating peptides has ballooned into the hundreds. They are also designing new peptides that bind" (lines 48-56).

So in the end it isn't necessary for the purposes of answering this question to establish that all three of those materials are semiconductor materials to which peptides have been found to bind. We are told that they have made progress in identifying "many additional organic compounds that bind to circuit-component materials." We therefore know that "Silicon, gallium arsenide, and indium phosphide are not the only semiconductor materials to which peptides have been found to bind."

[flowerpower]

I chose (B) because of the line in the second paragraph: "However, no known peptide was able to bind to semiconductor materials to cause the development..." I thought this implied that peptides' relationship to semiconductor materials had been previously studied.

[Jeff Wren]

Hi flowerpower,

Unfortunately, you made an unwarranted assumption here.

The second paragraph is describing Belcher and Hu's research. The prior sentence to the one that you cite describes Belcher/Hu's realization that "if they found peptides able to direct the crystal growth of the semiconductor materials that form transistors, they might have a tool for building nanoscale electronics" (lines 30-33). Based on the passage, this realization, that peptides may be able to be used in the assembly of nanocircuits, was their specific realization/contribution.

The sentence that you cite doesn't indicate that others had tested whether known peptides were able to bind to semiconductor materials. The way that I read it is that they tested this and found this to be the case, which is why they then "grew a random assortment of one billion different peptides" (lines 36-38) and tested those. I admit that this could have been more clearly worded, such as "they found that no known peptide was able to bind to semiconductor materials...."

The main support to eliminate Answer B actually appears in paragraph one. Describing the general research around using molecules that can work with nanocircuits, the passage states "Much current research is aimed at harnessing DNA to this end, but materials chemist Angela Belcher and physicist Evelyn Hu are investigating a different molecular pattern maker: peptides" (my emphasis)(lines 18-22). Since they are investigating peptides, which are a different molecular pattern maker than what the other researchers are investigating, that implies that they were the first/only ones investing peptides in this way. Otherwise, it wouldn't really be accurate to describe their focus on peptides as different.