Q20

[yoohoo081]

Could somebody explain why c is the answer for this question? I had hard time understanding why b is not the answer.

Thank you

[demetri.blaisdell]

Good question. I think (B) looks good at first, but let's take a deeper look.

I see two problems with (B). The first is "top from bottom." The passage does not mention determining this kind of orientation. It only discusses front/back orientation. The other problem is that the passage doesn't really discuss the difference between simple and complex creatures. In fact, simple creatures like fruit flies and nematodes have different methods of determining polarity. Lines 35-39 discuss differences in complexity of vertebrates; it doesn't compare all organisms in terms of how complex they are.

(C) brings in the similarity of the third paragraph with the differences discussed in the second paragraph. Animals are genetically very similar, but they determine polarity in different ways.

Let me know if you have any follow-up questions about this. I'm happy to go through other answer choices.

Demetri

[yoohoo081]

I see two problems with (B). The first is "top from bottom." The passage does not mention determining this kind of orientation. It only discusses front/back orientation. The other problem is that the passage doesn't really discuss the difference between simple and complex creatures. In fact, simple creatures like fruit flies and nematodes have different methods of determining polarity. Lines 35-39 discuss differences in complexity of vertebrates; it doesn't compare all organisms in terms of how complex they are.

Thank you for the explanation!
I see why C is the better choice, but I'm still little confused on B.
Lines 3-4 states must set up a way to distinguish its top from its bottom and its back from its front. Also, I thought it's different for complex and simple because of the examples given (human being more xomplex, still mystery, fruitfly- simpler etc)

Please clarify B please

[demetri.blaisdell]

Caught in a lie! I missed the reference to top/bottom polarity. The more important reason why (B) is wrong still stands, however. The problem is that the passage doesn't say that the method of determining polarity depends "on whether the organism is simple or complex." Fruit flies are clearly a simple organism yet they have a different mechanism than nematodes, another simple organism. There is a contrast between frogs and more complex vertebrates such as mammals (lines 35-39) but look closer: researchers don't know how mammals develop polarity.

The fruit fly vs. nematode problem and the fact that we don't actually know how complex organisms develop polarity make (B) an incorrect answer choice. Let me know if you buy that explanation.

Demetri

[callmejinny]

Hi,

Can someone tell me why (A) is a wrong?
Specifically, can someone clarify the difference between "overall genetic makeup" in (A) and "sets of essential genes" in line 46?



Thanks in advance.

[maryadkins]

I am not sure where you would get support for (A). I don't see anywhere in the passage that the author states that species differ MORE in embryonic mechanisms than in their overall genetic makeup. Even in lines 45-47, which state that once the embryo develops polarity, it relies on "essential genes" that are similar across species doesn't mean that OVERALL the species' entire genetic makeups are the same. It just means these few, essential genes are the same. Apart from these genes, we could still have very different genetic makeups, overall!

As for the other wrong answer choices that haven't yet been discussed on this thread:

(D) makes it way too specific, about the cytoplasm of the egg versus the p-granules of the sperm. This is definitely not a main point.

(E) is contradicted. Mechanisms are different across organisms.

Hope this helps clarify.