#25 - Must Be True, Purpose

[jgabalski]

Can someone please explain why answer choice D is stronger than answer choice C? I basically narrowed the question down to those two choices, but I felt answer C was better supported in the text " Seasonal synchrony of Typhlodromus reproduction with the growth of prey....." I felt like the sentences prior t this one on lines 20 - 23 were providing evidence of the synchrony sentence after them, and consequently chose choice C.


Thank you for the help.

[Jonathan Evans]

Hi, jgabalski,

Excellent question and good job narrowing it down to these two "contenders." Let's start with the question task: We are instructed to find the reason why the author introduces the relative egg-laying rate of the two kinds of mites. This "local purpose" type question often leads us to ask the question, "Why?"

Why does the author bring up the relative rate at which the two species of mites lay eggs? Often for these kinds of "why" questions the answer can be found directly above the citation. Why does this work? Because if a quotation serves a specific purpose, it usually (but not always) offers some kind of support for an immediately preceding contention.

For instance, here go back up to the beginning of this topic, around line 15. Beginning here we notice that the author is discussing Typhlodromus's effectiveness as a predator. As we read forward, note that one factor that contributes to this effectiveness is the fact that its "population can increase as rapidly as that of its prey." Now we have the necessary context. The discussion that follows through line 23 backs up this contention about relative rate of population increase.

Let's prephrase an answer for why the author brings up the egg-laying ability of each kind of mite:

The author brings up the egg-laying ability to show a way that the T mites can reproduce at a rate to match that of the C mites.

Now focus on the difference between answer choices (C) and (D). (C) focuses on the concept of "syncronicity" while (D) focuses on matching the rates. With this difference in mind, consider again the task of the question along with the prephrase. Why do we care about the egg-laying stuff? It has to do with the T mites effectiveness as C mite predators. "Syncronicity" might discuss what happens, but it fails to address why it happens.

I hope this helps!

[brcibake]

How is B incorrect? Is it because it is not specific as to what type of predatory mites? Don't the Typhodromus have a longer reproductive spam ( 8-10 days) vs the cyclamen mites (4/5 days)??
Thank you

[Adam Tyson]

Answer B is incorrect, brcibake, because the passage tells us nothing about what typically happens with predatory mites, only what typically happens with a specific type of predatory mite, Typhlodromus. Beware of overgeneralizing! For all we know, a typical predatory mite has a shorter reproductive life span than a cyclamen mite, and Typhlodromus is atypical in that regard.

[lilmissunshine]

Hello,

I just wanted to add on to Jonathan's explanation on why (C) is incorrect. I thought "synchrony" in (C) referred to the seasonal synchrony instead of reproductive rate and that's why it's an inferior answer. Is that right?

[Adam Tyson]

I think that is good additional support for eliminating C, lilmissunshine. Nice!

[HarryK]

2019 Bible Pg. 390 Typhlodromus

Hi,

When you explain question 25 choice (A), you say that this answer choice is incorrect. I assume that you meant: laying three eggs per day over 4~5 days and laying two or three eggs per day over 8~10 days are not laying eggs "at approximately equal rate"). Could you explain to me why these two are not equal rates in more detail? (I thought they were equal rates; but I still eliminated (A) because the passage would then only claim that C and T both reproduce by parthenogenesis and they reproduce at equal rates, which does not amount to "If reproduce by parthenogenesis, they reproduce at equal rates").


Thank you,
Harry

[KelseyWoods]

Hi Harry!

I can tell you're definitely reading your RCB closely! Here are my thoughts on your thoughts:

With the numbers listed in those lines, it does not seem that the two mites reproduce at equal rates. Cyclamen mites lay 3 eggs/day over 4 or 5 days (so 12 or 15 eggs total during the reproductive life span); whereas Typhlodromus lays 2-3 eggs/day over 8-10 days (so 16-30 eggs total during the reproductive life span). Thus, in a given reproductive cycle, it seems that Typhlodromus is somewhat outpacing Cyclamen mites. Of course, you could argue that these are approximately equal rates. But, as you say, it doesn't really matter because the purpose of providing those rates in lines 20-23 is not to support the claim that mites that reproduce by parthenogenesis do so at approximately equal rates. So the answer choice is incorrect regardless.

Best,
Kelsey