#22 - Biologist: When bacteria of a particular species are

[Administrator]

Please post below with any questions!

[MrMola]

I guessed A unfortunately Please explain how D is the correct answer.

[Adam Tyson]

Happy to help, MrMola! This argument is causal - the author presumes that the cause of the bacteria moving to the red zone is that it detects the highest level of energy production there. Energy production is the cause, movement to that area is the effect.

Answer D weakens that argument by showing that when the cause is present, the effect is absent - one of the five classic ways to attack a causal argument. In answer D, the same cause is present (energy production in an especially bright blue area is just as high as in a red area) but the effect is absent (the bacteria don't move to that area). Thus, energy production cannot, by itself, be the cause of the movement. It must be some other cause, or some combination of causes beyond just energy production.

When faced with a causal argument, if you are asked to weaken it, look for one of five things in the answer choices:

1. An alternate cause
2. The cause without the effect
3. The effect without the cause
4. A possible reversal of the cause and effect (the purported cause is really the effect, and the purported effect is really the cause)
5. Some problem with the data on which the author relied

[ser219]

I was stuck between D and E on this one and ended up choosing E.

I decided against D because of the line "the bacteria contain chlorophyll, a chemical that allows them to produce energy more effectively from this color of light than from any other. Use of the term effective lead me to think that D does not actually weaken the causal relationship because even if blue produces as much energy as red, it does not do so as effectively.

I liked E because I thought it showed an example where the effect was there but the cause was not. I am having trouble seeing why this is wrong.

Is a problem with my interpretation of D that the conclusion does not mention effectiveness? I am starting to see that now...

Thank you for the help!

[KelseyWoods]

Hi Ser219!

In this case, "more effectively" means basically the same thing as producing the more energy. Basically, the author has said that this shade of red is more effective than the other colors, but answer choice (D) says that the brightness of the light also affects energy production. So this brightly lit blue allows the bacteria to produce as much energy as it could from the more dimly lit shade of red. If the colors were equally lit, red would be better. The brighter light, however, allows the blue area to compensate. So, if bacteria are truly moving into areas only because they allow them to produce more energy (or produce energy most effectively), they shouldn't show a preference for dimmer red over brighter blue. Answer choice (D) weakens the argument by showing the cause (area that allows them to produce most energy) without the effect (moving into that area).

Answer choice (E) doesn't quite give us the effect without the cause. It removes the chlorophyll so you're correct that it removes the cause (no chlorophyll, no ability to produce energy more effectively from certain colors) but we don't know if the effect is still there. It just tells us that the bacteria move toward particular colors, but it doesn't tell us what these colors are. So we don't know if the bacteria are moving toward colors that would normally allow them to produce the most energy (like that shade of red) or if they're moving toward colors that wouldn't normally allow them to produce much energy. Answer choice (E) doesn't give us enough information to weaken this argument.

Hope this helps!

Best,
Kelsey

[OneSeventy2019]

PowerScore,

I had chosen C because I identified it as a "defender" argument - potentially warmth (and not energy produced by the shade of red) is what is "monitored" by the bacteria. Is that a fair assessment? Or am I missing something?

If choice C is in fact a defender argument? Can you explain the rationale for why we should chose a choice D over it? Does it have something to do with the fact that this is a causal argument?

Thanks!

[James Finch]

Hi One Seventy,

Could you explain what you mean by a "defender" argument? We use "defender" as a type of Assumption question, where the argument seems to be sound on it's (no clear logical holes) and so the correct assumption must come from outside the argument in the stimulus, but still affect its viability.

However, this question is a Weaken question, so we need to use a different set of tools to answer it correctly. That begins with seeing whether the stimulus contains causal reasoning: it does, as it infers a cause for why the bacteria move only to areas with the red light. So we have to use our causal weakening tools to attack the conclusion here, in order of most-to-least common:

1) An alternate cause for the effect, or;

2) Showing the same purported cause without the effect, or;

3) Showing the effect without the purported cause, or;

4) Show reverse causation (the purported cause is actually an effect of the purported effect), or;

5) An issue with the data or evidence used in the stimulus

Here the purported cause is the monitoring of the energy produced by chlorophyll, which leads to the effect of the bacteria moving to areas with more red light, where their chlorophyll is most effective at producing energy. Given that the cause isn't really supported by much evidence in the stimulus, I would Prephrase an alternate cause as the correct answer choice here, although Cause/No Effect or Effect/No Cause are also viable options.

(D) gives us a scenario where we have the same purported cause (energy produced) without the effect (bacteria moving), making it the correct answer.

Hope this clears things up!