Q22 - Microbiologist: Because heavy metals

[ohthatpatrick]

Question Type:
Strengthen

Stimulus Breakdown:
Conclusion: The bacteria's exposure to heavy metals in the sludge has promoted their resistance to antibiotics.
Evidence: Bacteria that survive in heavy-metal-filled sludge have evolved unusual ability to resist heavy-metal poisoning, and they show a strong resistance to antibiotics.

Answer Anticipation:
In abstract terms, this author seems to think that since X (bacteria) now shows trait A (resistance to heavy-metal poisoning) and trait B (resistance to antibiotics), it's probably the case that trait A caused trait B. This is quite dubious. Since the conclusion is causal, we should go to our two causal pressure points:
1. Is there some other way to explain the same evidence?
2. What additional info could impact the plausibility of the author's explanation?

For #1, we could say trait A and B are simply coincidental. Neither causes the other. We might also say that trait B causes trait A (resistance to antibiotics is what provides resistance to heavy-metal poisoning). Or perhaps it's simply some other factor, for example the ammonia in sewage sludge, that transforms the bacteria into being both trait A and B. Correct strengthen answers can simply rule out an alternative explanations.

#2 answers could sound like Covariation (cause/effect or no-cause/no-effect). It could sound like "bacteria in sludge that DOESN'T contain heavy metals, does NOT develop resistance to antibiotics". It could simply verify that supposed-cause comes before supposed-effect, "The bacteria did NOT have a resistance to antibiotics UNTIL it was subjected to heavy metal exposure". It could also provide other examples of this connection between heavy metals and antibiotic resistance, or it could explain the causal mechanism of how this would work, i.e. "the heavy metals ionize some of the ingredients in antibiotics, rendering them ineffective".

Correct Answer:
B

Answer Choice Analysis:
(A) Maybe. It sounds like a "no cause, no effect" type answer. Ultimately, this doesn't lean in either way to whether the antibiotic resistance or the heavy-metal resistance comes first. We want to think that heavy-metal resistance comes first, if we're calling it the cause of the eventual antibiotic resistance.

(B) Yes, this looks like a stronger version of the "no cause, no effect" answer. When not exposed to heavy metals, we generally don't see antibiotic resistance. This is a helpful way of making it seem more plausible that "exposure to heavy metals" makes a causal difference. It also indirectly plays a #1 role .. it rules out the idea that "maybe it's just some chemical, like ammonia, in the sludge that is causing these effects."

(C) This weakens by providing a Reverse Causality explanation.

(D) Irrelevant. We weren't saying that sewage sludge normally has antibiotics in it.

(E) This seems to weaken a tad by giving us a covariation mismatch. These bacteria are "no cause, effect". They're not exposed to the sewage sludge, but they still have the same observed traits.

Takeaway/Pattern: We're more likely to see #1 alternative explanations show up on Weaken / Flaw / Necessary Assumption. We're slightly more likely to see #2 plausibility answers show up on Strengthen. The most common type of answer that increases the plausibility of the author's causal story is a Covariation answer: evidence that cause/effect appear and disappear in tandem. When bacteria is in sludge but NOT exposed to heavy metals, it doesn't have these effects. That makes our scientific brain believe that "exposure to heavy metals" is a causal difference maker. This answer is essentially 'the control group'. If you want to figure out whether heavy metals make a difference, keep the rest of the scenario the same (still study bacteria in sewage sludge) and see if the observed traits of A and B are still present.

#officialexplanation

[irenewerwerwer]

I was really nervous during preptest and lost this one. I reread it and analyze the question as follows, please help confirm whether my analysis to the point, thanks!

premise:
expose to heavy metal--> resist metal poison ("because")
show: resist antibio (the argument did not suggest any obivious relation between resist anbitio & expose to metal)

conclusion:
expose to heavy metal--> resist antibio

I prephrase the correct answer should convey:
resist metal poison--> resist anbio

C,D,E are obviously wrong. Narrow down to A and B:
A: ~resist antibio--> ~ resist metal poison
= resist metal poison --> resist antibio
the same as prephrase
B: ~expose--> ~resist metal poison + ~ resist antibio
= resist metal poison / resist antibio --> expose
seems within the scope but does not help strengthen the gap between premise and conclusion, therefore incorrect.

Any thought would be appreciated!

[jennifer]

I got this answer correct through the process of elimination, but I also think I was lucky. Why is answer choice A correct? Does A strenghten because it explains that both bacteria are similar?

B. is out of scope
C. Is a premise booster
D. Made no sense why does the sludge have antibiotics.
E. Out of Scope.

Thank you.

[chike_eze]

I got this answer correct through the process of elimination, but I also think I was lucky. Why is answer choice A correct? Does A strenghten because it explains that both bacteria are similar?

B. is out of scope
C. Is a premise booster
D. Made no sense why does the sludge have antibiotics.
E. Out of Scope.

Thank you.

Correct answer here is actually B. I would appreciate a full explanation in support of B. For some reason, I thought (A) provided support similar to how I've read that (B) provides support for the argument. (a bit confused)

[americano1990]

The conclusion is causal. Heavy metal contributes to resistence to antibiotics.
Make this simpler:
Heavy Metal---> (causal arrow) Resist. to Antibio

There are several ways to strengthen a causal relationship that i cant regurgitate here (need Lsat GEEKS for that !!) but the one that applies in this question is: absence of cause leads to absence of effect

thats what (B) does: if not exposed to heavy metals, bacteria dont develop resistence to antibio. It doesnt prove, but still implies to a certain extent that heavy metal exposure may at least be playing some role.

Contrast that with (A). All it tells us is that there is a correlation between heavy metal and antibio, but its not enough to support our claim that heavy metal--> (causal) resistence to antibio.
(A) is perfectly compatible with the arrow going in the opposite direction.

Hope this helps.

[vik]

To strengthen a causal claim, show that when the cause does not occur, the effect does not occur. B does this.

Never take the contra-positive (which A does) becuase in a causal claim, the cause is the necessary element, not the effect.

[giladedelman]

Yep, I agree with those of you who chimed in with answers.

We can take an important lesson away from this question. As you guys pointed out, one way to strengthen a causal argument is to say, When you don't have the cause, you don't have the effect. That's why answer (B) is correct, and you're going to see that a lot on strengthen/weaken questions that involve causal arguments.

Interestingly, answer (D) would weaken the argument by suggesting an alternative explanation: maybe it's not the heavy metals concentration, maybe it's the fact that there's also a high antibiotics concentration.

Vik, nice explanation on (A); good point about how the cause is actually the necessary condition. In general, let's not get too gung-ho about diagramming everything out when we're not actually dealing with conditional statements.

(C) doesn't really affect the argument, because it doesn't impact where this resistance to antibiotics comes from.

(E) would, if anything, weaken the argument by saying you can have this result even without the cause ... but it doesn't really do much since "many" is so vague.

Good job!

[dean.won]

Yep, I agree with those of you who chimed in with answers.

We can take an important lesson away from this question. As you guys pointed out, one way to strengthen a causal argument is to say, When you don't have the cause, you don't have the effect. That's why answer (B) is correct, and you're going to see that a lot on strengthen/weaken questions that involve causal arguments.

Interestingly, answer (D) would weaken the argument by suggesting an alternative explanation: maybe it's not the heavy metals concentration, maybe it's the fact that there's also a high antibiotics concentration.

Vik, nice explanation on (A); good point about how the cause is actually the necessary condition. In general, let's not get too gung-ho about diagramming everything out when we're not actually dealing with conditional statements.

(C) doesn't really affect the argument, because it doesn't impact where this resistance to antibiotics comes from.

(E) would, if anything, weaken the argument by saying you can have this result even without the cause ... but it doesn't really do much since "many" is so vague.

Good job!

thx for explanation.

so D is an alternate cause b/c its NOT exposure to HM that causes resistance to AB but direct exposure to AB that makes them resistant to it?

[Dkrajewski30]

In a moment of overconfidence, I selected A and moved on, despite no need to rush through the question or section. I thought I'd write the following to give a better idea to any others who may have selected A, as to why it's wrong.

The cause the argument posits is sludge with heavy metals in it. What do its effects appear to be? The ability (through evolutionary means) to resist heavy-metal poisoning as well as the ability to resist antibiotics. So here was my way of thinking about this causal relationship: Sludge causes two abilities. Why? Because it enabled bacteria to have ability 1, and the same bacteria have developed ability 2. So might it be reasonable to suspect that because sludge caused ability 1, that it caused ability 2 as well? After all, the argument hasn't suggested any other possible causal explanations, or anything else with potential causal power, other than the two effects of the alleged cause (the sludge). But that's just it, isn't it? On the LSAT, if a causal relationship is posited, of course the argument fails to consider possible other causal explanations. Maybe ability 1 (the resistance to heavy metal poisoning) is causing the resistance to antibiotics, or ability 2. So it's not the sludge that has causal power as it pertains to ability 2. It's one of the products of the sludge that has the causal power, if we grant, anyway, the assumption that the sludge did indeed cause ability 1. So that's interesting. We can grant that the sludge has some causal power, but we can still deliver a decisive blow to the argument by pointing out that it's the resistance to poisoning that actually caused the resistance to antibiotics, as opposed to the cause that the argument posits (the sludge).

Anyhow, A is wrong because it doesn't address what the argument claims to have all the causal power - the sludge! The sludge just isn't mentioned at all in this answer, and so for that reason, you can quickly eliminate it. So what if bacteria without ability 1 don't have ability 2? Are these bacteria contained in heavy metal sludge or not?

On a general note, it seems to help the argument if we suppose that when we have the sludge, we get both abilities 1 and 2, as we want to strengthen the claim that the sludge causes both abilities. If neither abilities are there when the sludge is, then then the effects are absent when the alleged cause is present, so that's a problem, and that consideration would significantly weaken the argument. If, however, both abilities are there when the sludge is, then the effects are there when the alleged cause is, and that would strengthen the causal relationship. Answer choice B actually does something similar. But instead of going the 'positive' direction of proof (showing the effects with the cause), it goes the 'negative' direction, by showing that without the effects, there's no cause. And that's another consideration that strengthens. Anyway, I'm getting carried away. A. is wrong because it doesn't address the alleged cause. Plain and simple.

[austindyoung]

If we imagine the stimulus to be conditional and not causal, (A) would still be wrong because you can't take the contrapositive of a "most" statement. Tricky.

[vanessa.m.leigh]

To strengthen a causal claim, show that when the cause does not occur, the effect does not occur. B does this.

Never take the contra-positive (which A does) becuase in a causal claim, the cause is the necessary element, not the effect.

The conclusion is causal. Heavy metal contributes to resistence to antibiotics.
Make this simpler:
Heavy Metal---> (causal arrow) Resist. to Antibio

There are several ways to strengthen a causal relationship that i cant regurgitate here (need Lsat GEEKS for that !!) but the one that applies in this question is: absence of cause leads to absence of effect

thats what (B) does: if not exposed to heavy metals, bacteria dont develop resistence to antibio. It doesnt prove, but still implies to a certain extent that heavy metal exposure may at least be playing some role.

Contrast that with (A). All it tells us is that there is a correlation between heavy metal and antibio, but its not enough to support our claim that heavy metal--> (causal) resistence to antibio.
(A) is perfectly compatible with the arrow going in the opposite direction.

Hope this helps.

Could someone please explain why the cause would be the necessary element? I'm confused as to how this would be diagrammed. Resistance to antibiotics --> resistance to heavy metal poisoning seems counterintuitive to me

[tommywallach]

Hey Vanessa,

I'm not sure I understand your question. Causation is not inherently a necessary condition:

X --> Y means that X causes Y, not that X is necessary to get Y.

Anyway, this question has been diagrammed already, as in the post you quote.

-t

[vanessa.m.leigh]

Hi Tommy,

Thanks for the reply. I'm still confused though - I took Vik's post to mean that a cause is the necessary element in a causal relationship (sufficient --> necessary) i.e. Effect --> Cause, or in this case Resistance to antibiotics (effect) --> Resistance to heavy metal poisoning (cause). I also don't understand why we can't take the contrapositive of a causal claim ... can we treat causal relationships the same as conditional statements?

Many thanks

[tommywallach]

Hey Vanessa,

Ignore Vik. : )

I still don't understand what sufficient --> necessary means. Sufficient and necessary conditions are TOTALLY different issues, whereas an arrow implies a conditional relationship. Anyway, if a passage says that X always causes Y (and requires nothing else to cause Y), then you could say that X --> Y, and the contrapositive would be -Y --> -X. However, you can't say Y --> X, because we have no reason to believe that Y can only be caused by X. Make sense?

-t

[ttunden]

Microbiologist is implying causation

one way to strengthen causation is showing no cause + no effect

answer choice B does this

JENNIFER please next time do not post the wrong answer as correct. Manhattan is infamous for doing this. You're about to give a young male a heart attack!

[selimazing]

Here is my explanation.

The argument is as follows:

Because there is a high concentration of heavy metals in the sewage the bacteria that live there have developed the ability to resist heavy-metal poisoning.

That same bacteria (that is resistant to heavy-metal poisoning) ALSO shows a strong resistance to antibiotics.

Conclusion: Bacteria's exposure to the heavy metals promoted (caused/responsible for/) their resistance to antibiotics.

Basically, its saying that there is a causal connection between exposure to heavy metals----->resistance to antibiotics.

Think about how to strengthen any argument. Here are some of the ways you can do that with this question.

(1) Demonstrate that when there are no heavy metals present the bacteria do not develop resistance to heavy metal poisoning and thus no antibiotic resistance [no cause ----> no effect --in other words, if you remove the heavy-metal resistance then you don't get antibiotic resistance.

(2) the relationship between heavy-metal poisoning resistance and antibiotic resistance is NOT a coincidence (coincidental link).

(3) the antibiotic resistance that is NOT promoting the resistance to heavy-metal poisoning (relationship is NOT reversed)

The correct answer choice plays on the first possible way to strengthen the argument. If you don't have heavy metals present then these bacteria do not develop heavy metal poisoning which leads to no resistance to antibiotics either.

Always focus on the conclusion!!

[mkd000]

I'm still a bit confused as to why (A) is incorrect. This is the reasoning I have come to reach in terms of why (A) is incorrect: (A) is about "Most bacteria" (in general), and the stimulus is not about "most bacteria" - the stimulus is speaking about those bacteria that survive in the sludge and are resistant to heavy metal poisoning. In this sense, this answer choice is out of scope.

Can a Geek please address my reasoning so that I know whether or not my thought process is going in the right direction?

Thanks.

[rinagoldfield]

Tough question!
(B) strengthens because it knocks out a very specific possibility the author overlooked.
Let’s check back in with the argument core:

Bacteria in high-metal sewage develop both metal resistance and antibacterial resistance
-->
Exposure to the metals causes the antibacterial resistance

The author overlooks here that the antibacterial resistance may have caused the metal resistance, or, crucially, that the sewage itself caused the antibacterial resistance!

(B) knocks out the possibility that the sewage itself caused the antibacterial resistance. (B) thus strengthens.

(A) strengthens the correlation between metal resistance and antibacterial resistance, but it does not address the causal argument. We still don’t know what caused what, and (A) doesn’t narrow it down at all.

Here’s an analogy:

Babies who were played Mozart did better in school than those who did not
-->
Playing Mozart to babies causes them to do better in school.

The author overlooks that parents who play Mozart to their babies may generally value school more than other parents, or that these parents are generally wealthier than other parents. Perhaps the values, or the wealth, caused the kids to do well in school.

An analogous answer choice to (B) would say “Kids who grew up in circumstances very similar to those of the kids who listened to Mozart, but without Mozart, do badly in school.” This knocks out the specific possibilities outlined above.

(A), on the other hand, would say “Most kids who do badly in school did not listen to Mozart.” This strengthens the correlation in the premise, but it tells us nothing about what caused what!

Hope this helps!