Microbiologist: Because heavy metals are normally concentrated in

+1 for B. The others don't strongly indicate a "causal relationship" between the presence of metals and antibiotics. Only B does so. It does so by eliminating the possibility of the effect occuring without the occurence of the cause.

Posted from my mobile device

Posted from my mobile device

+1 For B. Bacterial exposed to heavy metals>resistant to antibiotics. B says-Bacteria not exposed to heavy metals>not resistant to antibiotics.

Bumping for discussion. A really fun LSAT question that should be discussed a little more.

Someone please explain why not C?

Posted from my mobile device

Hi,

Can anybody explain why A is incorrect?

Microbiologist: Because heavy metals are normally concentrated in sewage sludge during the sewage treatment process, the bacteria that survive in the sludge have evolved the unusual ability to resist heavy-metal poisoning. The same bacteria also show a strong resistance to antibiotics. This suggests that the bacteria’s exposure to the heavy metals in the sewage sludge has somehow promoted their resistance to antibiotics.

Premise: Heavy metals are normally concentrated in sewage sludge during the sewage treatment process
Premise: The bacteria that survive in the sludge have evolved the unusual ability to resist heavy-metal poisoning
Premise: The same bacteria also show a strong resistance to antibiotic
Conclusion: This suggests that the bacteria’s exposure to the heavy metals in the sewage sludge has somehow promoted their resistance to antibiotics

-- Fairly straightforward question, in terms of set up. We just want show that either the heavy metals caused the antibiotic resistance, or that there is something that can strengthen this connection. My initial thought, which ended up correct, was that the answer was going to show how one caused the other.


Which one of the following, if true, most strengthens the microbiologist’s argument?

(A) Most bacteria that are not resistant to antibiotics are not resistant to heavy-metal poisoning either. -- This is incorrect because we do not know which caused the other. It could very well be that the antibiotic resistance caused the metal poisoning resistance. Do not assume anything!

(B) Bacteria that live in sewage sludge that is free of heavy metals, but is in other respects similar to normal sewage, are generally resistant to neither heavy-metal poisoning nor antibiotics. -- Perfect! So in the absence of the metal, we are told that the bacteria no longer has either; this means that the metal is the cause of both and thus is our answer.

(C) Antibiotic resistance of bacteria that survive in sewage sludge in which heavy metals are concentrated contributes to their resistance to heavy-metal poisoning. -- This says the opposite of what we want. This says the antibiotics cause the metal resistance. Classic trap answer.

(D) Sewage sludge that contains high concentrations of heavy metals almost always contains significant concentrations of antibiotics. -- And? So we are told that there are a few key elements, but we once more have no idea how these affect our bacteria, or the cause. We would have to assume a few things and then make the same assumption we did in (A) just to make this work.

(E) Many kinds of bacteria that do not live in sewage sludge are resistant to both heavy-metal poisoning and antibiotics. -- Cool, but who cares? We want to know about those that DO live in the sludge and are resistant to both. So this is out.

Certainly an engaging question. A single read of the options was not enough and I did come back to review the options again before choosing (B)!

Sewage sludge has heavy metals.
Bacteria that survive in it are resistant to heavy metals.
Same bacteria also show a strong resistance to antibiotics

Conclusion: Bacteria’s exposure to the heavy metals in the sewage sludge has promoted their resistance to antibiotics.

We need to strengthen that heavy metals in the sludge has led to antibiotic resistance.
Exposure to Heavy metals in sludge (cause) -> Resistance to antibiotics (effect)

(A) Most bacteria that are not resistant to antibiotics are not resistant to heavy-metal poisoning either.

We have to establish that exposure to heavy metals leads to resistance to antibiotics.
The fact that 'no resistance to antibiotics' and 'no resistance to heavy metal poisoning' co-exist doesn't help in establishing that heavy metals resistance leads to antibiotic resistance. It might show that there may be a relation between 'resistance to antibiotics' and 'resistance to heavy metal poisoning' but it does not show that 'resistance to heavy metal poisoning' is the cause of 'resistance to antibiotics'.

(B) Bacteria that live in sewage sludge that is free of heavy metals, but is in other respects similar to normal sewage, are generally resistant to neither heavy-metal poisoning nor antibiotics.

Imp point here - Bacteria that live is sewage sludge similar to this one but without heavy metals. So the distinction is heavy metals. These bacteria are not resistant to antibiotics. Then it does seem that resistance to heavy metals is the cause of resistance to antibiotics. It does strengthen our conclusion.

(C) Antibiotic resistance of bacteria that survive in sewage sludge in which heavy metals are concentrated contributes to their resistance to heavy-metal poisoning.

Incorrect. This establishes the opposite relation - that 'antibiotic resistance' causes 'resistance to heavy-metal poisoning'. Our conclusion establishes the opposite relation.

(D) Sewage sludge that contains high concentrations of heavy metals almost always contains significant concentrations of antibiotics.

Irrelevant. If anything, it may weaken our conclusion. If presence of heavy metals and presence of antibiotics happens together, it may be that the bacteria are developing resistance of antibiotics because they are exposed to them. Then heavy metal resistance may not be leading to antibiotic resistance.

(E) Many kinds of bacteria that do not live in sewage sludge are resistant to both heavy-metal poisoning and antibiotics.

Doesn't help. We don't know what is the cause and what is the effect. It just tells us that the two co-exist. Doesn't help our conclusion that 'resistance to heavy metal poisoning' is the cause of 'resistance to antibiotics'.

Answer (B)

Microbiologist's argument: The bacteria’s exposure to the heavy metals in the sewage sludge has somehow promoted their resistance to antibiotics.

So we're looking for an answer choice that can explain the connection between exposure to heavy metals and resistance to antibiotics. The microbiologist believes:

Exposure to heavy metals --> resistance to antibiotics

Let's go through the choices:

(A) Most bacteria that are not resistant to antibiotics are not resistant to heavy-metal poisoning either.

We're not concerned with bacteria that are not resistant to antibiotics -- we're looking for the group that is resistant to antibiotics.

(B) Bacteria that live in sewage sludge that is free of heavy metals, but is in other respects similar to normal sewage, are generally resistant to neither heavy-metal poisoning nor antibiotics.

If bacteria that live in sewage sludge that is free of heavy metals are generally resistant to neither heavy-metal poisoning nor antibiotics, perhaps the bacteria’s exposure to the heavy metals in the sewage sludge does lead to their resistance to antibiotics. Let's keep this one.

(C) Antibiotic resistance of bacteria that survive in sewage sludge in which heavy metals are concentrated contributes to their resistance to heavy-metal poisoning.

This choice suggests that antibiotic resistance --> resistance to heavy-metal poisoning. The order here is reversed. C is out.

(D) Sewage sludge that contains high concentrations of heavy metals almost always contains significant concentrations of antibiotics.

This doesn't strengthen the idea that exposure to heavy metals --> resistance to antibiotics. D is out.

(E) Many kinds of bacteria that do not live in sewage sludge are resistant to both heavy-metal poisoning and antibiotics.

Out of scope -- we're looking for bacteria that do live in sewer sludge.

B is the answer.

Source: PowerScore Forum

Strengthen—CE. The correct answer choice is (B)

The microbiologist argues that since bacteria that live in sewage sludge that contains heavy metals are resistant to both heavy metal poisoning as well as to antibiotics. The microbiologist then concludes that the exposure to heavy metals has caused the resistance to antibiotics. The causal indicator word is “promoted,” which the author uses to indicate that the exposure caused the resistance. We can diagram the relationship as follows:

Cause ..... ..... ..... ..... ..... ..... Effect

Exposure to heavy metals ..... :arrow: ..... Resistance to antibiotics

The author does not provide much information to support the existence of a causal relationship between exposure and the resistance. It does support a correlation; that the two occur together. To strengthen this argument, we need to strengthen the causal relationship by (1) reducing the likelihood of an alternate cause, (2) reducing the likelihood that the cause occurs without the effect, (3) reducing the likelihood that the effect occurs without the cause, or (4) reducing the likelihood that the cause and effect are reversed.

Answer choice (A): Though this answer choice looks tempting, as it seems to connect heavy metal resistance to antibiotic resistance, it does not connect exposure to heavy metals with resistance to antibiotics. The idea of exposure is central to the causal relationship, and since this answer choice just connects resistance to heavy metals to resistance to antibiotics, it does not strengthen the causal relationship in the stimulus.

Answer choice (B): This is the correct answer choice. It states that without exposure to heavy metals, bacteria generally are not resistance to heavy metals or antibiotics. It strengthens the argument by saying that when the cause does not occur, the effect also does not occur. Thus, by reducing the likelihood of the effect occurring without the cause, it is correct.

Answer choice (C): This answer choice does not support the causal relationship. Remember that causal relationships only go in one direction, with the cause occurring prior to the effect. This answer choice suggests that the antibiotic resistance itself caused heavy metal poison resistance, which is not the causal relationship concluded by the microbiologist.

Answer choice (D): Even if the sludge contains antibiotics, it does not support that the resistance to antibiotics came from the exposure to the heavy metals. In fact, if the sludge contained both heavy metals and antibiotics, it would be more difficult to determine if the resistance came from exposure to heavy metals, antibiotics, or some combination.

Answer choice (E): Bacteria can be exposed to heavy metal other than in sludge. The causal relationship is not specifically limited to situations where the exposure to heavy metals occurred in sludge. This answer choice actually has no impact on the argument, because we do not know if the bacteria were exposed to heavy metal or not.