Microbiologist: Because heavy metals are normally concentrated in sewage sludge during the sewage treatment process, ...

Ava on February 9, 2020


Can someone give an explanation of the answer choices A-E? What I understand as the flaw in the argument is that it there could be something else that is promoting antibiotic resistance that it is not necessarily true that heavy metals and antibiotic resistance are correlated. When I look at the answer choices, particularly B and C, the way they are written in my mind reads very similar. It would be especially helpful if someone could break down why C is wrong and B is right. Thank you!

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Skylar on February 9, 2020

@shafieiava, happy to help!

Your understanding of the passage's weakness is correct. How do we know that the exposure to heavy metals is what is specifically causing the bacteria's resistance to antibiotics?

(A) is incorrect because bacteria that are not resistant to anything and are not necessarily located in sewer sludge are largely irrelevant to the subject of our argument.

(B) is correct because it shows that bacteria in sewage sludge without heavy metals lack both resistance to heavy-metal poisoning and to antibiotics. This singles out heavy metal exposure as the only difference that could promote antibiotic resistance and eliminates other factors that could have potentially caused the antibiotic resistance- such as sewage sludge or the general nature of the bacteria. In turn, this strengthens the explanation provided by the passage.

(C) is incorrect because it starts from the point of having antibiotic resistance. Rather than arguing that exposure to heavy metals promotes antibiotic resistance, (C) argues that antibiotic resistance promotes heavy metal resistance. This does not help to explain anything about how the antibiotic resistance was promoted.

(D) is incorrect because it is irrelevant. If anything, the presence of antibiotics in the sludge may suggest its own incentive for bacteria to develop a resistance, thereby weakening the passage's argument.

(E) is incorrect because it discusses a different and irrelevant subset of bacteria. If anything, this may imply that all bacteria is already resistant to antibiotics and heavy metals, which weakens the explanation provided by the passage.

Does that make sense? Please let us know if you have any other questions!