Aptamers—synthetic DNA or RNA molecules that bind to target molecules—can be used to test for foodborne bacterial pathogens, though their...
GMAT Information and Ideas : (Ideas) Questions
Aptamers—synthetic DNA or RNA molecules that bind to target molecules—can be used to test for foodborne bacterial pathogens, though their specificity (the probability of returning a negative result in the absence of the focal pathogen) in real-world foods has been unclear. Sandeep Somvanshi et al. fabricated test paper incorporating aptamers targeting strain O157 of the bacteria Escherichia coli; the paper shifts from pink to purple as the aptamers bind to target molecules. Somvanshi et al. tested the paper in store-bought pear juice they treated with E. coli O157, other strains of E. coli, or other bacteria species. Following exposure, the paper from the O157 test was purple while papers from the other tests were pink, suggesting that ______
Which choice most logically completes the text?
aptamer-based tests in real-world foods are more likely to show a high degree of specificity if the focal pathogen is E. coli O157 than if the focal pathogen is another strain of E. coli or another species.
uncertainty about the specificity of aptamer-based tests for pathogens in real-world foods may be due to the similarity between E. coli O157 and other E. coli strains.
the specificity of the tests in a real-world food was unaffected by the aptamers' tendency to bind to different strains of E. coli.
the aptamers successfully bound to E. coli O157 and the tests displayed a high degree of specificity in a real-world food.
Step 1: Decode and Map the Passage
Create Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| "Aptamers—synthetic DNA or RNA molecules that bind to target molecules—can be used to test for foodborne bacterial pathogens, though their specificity (the probability of returning a negative result in the absence of the focal pathogen) in real-world foods has been unclear." |
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| "Sandeep Somvanshi et al. fabricated test paper incorporating aptamers targeting strain O157 of the bacteria Escherichia coli; the paper shifts from pink to purple as the aptamers bind to target molecules." |
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| "Somvanshi et al. tested the paper in store-bought pear juice they treated with E. coli O157, other strains of E. coli, or other bacteria species." |
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| "Following exposure, the paper from the O157 test was purple while papers from the other tests were pink, suggesting that ______" |
|
Provide Passage Architecture & Core Elements
Main Point: A study tested aptamer-based pathogen detection in real food and found the aptamers successfully identified their target while avoiding false positives.
Argument Flow: The passage starts by noting uncertainty about aptamer specificity in real-world foods, then describes a study that tested this directly using pear juice with different bacterial conditions, leading to clear results that distinguish the target pathogen from non-targets.
Step 2: Interpret the Question Precisely
This is a fill-in-the-blank question asking us to choose the best logical connector. The answer must create the right relationship between what comes before and after the blank.
Step 3: Prethink the Answer
- Looking at our results analysis, we saw that the O157 test turned purple (indicating binding) while all the other tests stayed pink (indicating no binding)
- This tells us two important things: first, the aptamers successfully detected their target (E. coli O157), and second, they didn't bind to the wrong targets (other E. coli strains or other bacteria species)
- The passage started by noting that aptamer specificity in real-world foods "has been unclear," so these results directly address that uncertainty
- The results show both successful target detection and high specificity—the aptamers did exactly what they were supposed to do in a real food environment
- So the right answer should indicate that the aptamers worked well, binding to their target while showing good specificity in a real-world food setting
aptamer-based tests in real-world foods are more likely to show a high degree of specificity if the focal pathogen is E. coli O157 than if the focal pathogen is another strain of E. coli or another species.
• ✗ Incorrect
- Claims O157 aptamers are more likely to be specific than aptamers for other targets
- Goes beyond what we can conclude from this single study
- We only tested O157 aptamers, so we can't compare their performance to hypothetical aptamers for other targets
uncertainty about the specificity of aptamer-based tests for pathogens in real-world foods may be due to the similarity between E. coli O157 and other E. coli strains.
• ✗ Incorrect
- Suggests uncertainty about specificity might be due to similarity between E. coli strains
- Contradicts the results—the test clearly distinguished O157 from other E. coli strains
- The results actually resolve uncertainty rather than explain it
the specificity of the tests in a real-world food was unaffected by the aptamers' tendency to bind to different strains of E. coli.
• ✗ Incorrect
- Says specificity was "unaffected by the aptamers' tendency to bind to different strains"
- Makes no sense—the whole point is that aptamers DON'T bind to different strains
- Misrepresents what specificity means
the aptamers successfully bound to E. coli O157 and the tests displayed a high degree of specificity in a real-world food.
• ✓ Correct
- States the aptamers successfully bound to E. coli O157 (purple result confirms this) and notes the tests showed high specificity in real-world food (only bound to target, not other bacteria)
- Directly addresses the passage's opening concern about unclear specificity in real foods
- Matches exactly what the experimental results demonstrated