Reading comp PrepTest 121 · Section 3 · Question 20

Topic: Science

Paragraph 1

• Paragraph note
  • Process described; comparisons
• Views, minor Meta-Structures, and the author's attitude
  • Process - Polarity - First thing embryos do - Determine front/back; top/bottom
  • Comparison - Process of polarity is different across organisms; later development (e.g., limbs, brains) much more similar
  • Examples - Fruit flies, nematodes, humans

Paragraph 2

• Paragraph note
  • Examples/Contrasts; Question
• Views, minor Meta-Structures, and the author's attitude
  • Example 1 - Fruit fly - Polarity determined before fertilization, happens quickly after
  • Example 2 - Nematode - Polarity determined by location of fertilization; p-granules form and decide front/back
  • Example 3 - Frogs - Similar to nematodes
  • Example 4 - Humans - Polarity determined much later
  • Question - How is it determined in humans? (“tempting mystery”)

Paragraph 3

• Paragraph note
  • Similarities after polarity determined; Paradox
• Views, minor Meta-Structures, and the author's attitude
  • Post-polarity genes are similar across species
  • Example - Eye genes are similar in flies, mice, humans
  • Paradox - When most similar (embryo), use different mechanisms; when most different (identifiable species), use the same mechanisms

Main Point: While later development of organisms across species relies on similar genes for similar functions/body parts, early embryonic development of polarity shows a variety of different mechanisms across those same species.

Lines 1-4 - Process defined

Lines 4-8 - Process compared between species and to other processes

Lines 42-44 - Question/mystery raised

Lines 45-47 - Lines 45-46 - Shift to discussing similarities

Lines 51 - 57 - A paradox

Phenomenon/Explanation - As with many (if not most) Science passages, this one features a phenomenon - the determination of polarity (Lines 1-4) - that needs an explanation. In this case, the Author offers explanations for how polarity is determined - but these processes are very different between organisms (Lines 4-7), which leads us to our next two Meta-Structures...

Comparisons - The passage includes two sets of comparisons that are directly connected, and they’re summed up in Lines 4-8. The Author says that the mechanisms to determine polarity are far more different between organisms than are the processes for later development. So, in other words, organisms have different processes for determining polarity, and similar processes for later development. Which leads us to...

Generalization/Examples - That comparative statement is a Generalization, and the Author then dives into many examples of the different processes of determining polarity (Paragraph 2), and an example of the similar later processes in Lines 49-51. This generalization and these examples all build to...

Paradox/Resolution - The Author explicitly references a paradox, starting in Line 51. That paradox? When species are most similar (embryos, just a few cells), the processes they use to develop are the most different; when they’re most different (developed enough to tell the different species), the processes they use to develop are the most similar. The Author doesn’t present an explanation or resolution for why this might be so, so the Paradox itself is the point of this discussion!

Meta-Structure Wrap-Up - All of these Meta-Structures are substantial in the passage and relate to each other, so they’re all related to the main point. Phenomenon/Explanation passages tend to have the Author’s explanation serve as the main point. Comparison passages tend to have that type of language featured in the main point. Generalization/Examples passages tend to have the generalization as the main point, and Paradox/Resolution passages tend to have the resolution, when one is offered, as the main point - otherwise, the paradox itself is the main point. All of these Meta-Structures deal with the same central topic - the similarities and differences between processes of various species at different stages of development, and particularly the differences in how polarity is determined. Bringing all of this together leads us to the main point, as we summarized it above (and also see the Last Thoughts? note).

Question/Answer - The Author ends Paragraph 2 with a “tempting mystery,” suggesting a question that researchers will be interested in investigating - how polarity is established in mammals. No answer is presented, and no research is offered to indicate a potential answer. Since this is a small line that doesn’t support a broader view or have an answer provided, it’s likely to show up in only a single question.

Note how we phrased the main point - it reflects the paradox and comparisons, but it puts the information about the similarities later first, and the differences earlier last. That’s because the focus on the passage is on that earlier process of determining polarity - it kicks off the passage, and it serves as the focus of that very long Paragraph 2.

Also, this passage is notoriously difficult, but note that it’s very much based on the comparative generalization - the entire Paragraph 2 is meant just to back up a part of that generalization! While the examples themselves can be tricky, and there’s a lot of science involved (what’s a p-granule?!!?!), we don’t really need to know that science - just that the passage is presenting different ways that polarity is determined in different species. Let’s keep this big-picture in mind as we approach the questions.