Reading ComprehensionDifficulty: Hard

PT121 S3 P4 Q21 Explanation

Embryo Polarity

A free, expert breakdown of this official LSAT Reading Comprehension question.

TopicsAuthor OpinionScience

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Passage

The first thing any embryo must do before it can develop into an organism is establish early polarity—that is, it must set up a way to distinguish its top from its bottom and its back from its front. The mechanisms that establish the earliest spatial configurations in an embryo are far less to be quite different from the polarity signals in the development of humans and other mammals.

In the fruit fly, polarity is established by signals inscribed in the yolklike cytoplasm of the egg before fertilization, so that when the sperm contributes its genetic material, everything is already set to go. Given all the positional information that must be distributed throughout the cell, it takes a fruit fly a among cells. Yet how polarity is established in mammals is currently a tempting mystery to researchers.

Once an embryo establishes polarity, it relies on sets of essential genes that are remarkably similar among all life forms for elaboration of its parts. There is an astonishing conservation of mechanism in this process: the genes that help make eyes in flies are similar to the genes that make eyes in or extremities and become identifiable as distinct species, the developmental mechanisms they use are remarkably similar.

What this question is testing

Author Opinion

Your task

Pin down exactly what the question asks about the passage — a detail, the author's view, the structure, or the main point — before looking at the choices.

Common trap

Answers that restate a true detail from the passage but don't answer the specific question being asked.

Winning move

Anticipate the answer in your own words from the passage, then find the choice that matches that prediction.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
21.

The passage suggests that the author would be most likely to agree with which one of

Answer choices

  1. Too Strong: more X, more Y11% picked this

    The simpler the organism, the greater the speed at which it develops from fertilized

    This Volume Dial formulation (the more X, the more Y) is the most extreme type of claim there is, because it extends infinitely in both directions. A 20-celled organism's embryo develops faster than a 21-celled organism's embryo does. An organism with 10 million cells develops faster than an organism with 11 million cells. There's nothing in the passage that lets us say that for all life forms (that go from egg to embryo), the simpler it is, the faster it develops.

  2. Too Strong: most10% picked this

    Scientists have determined how polarity is established in most

    The word "most" is one of the most frequent killers of answer choices in Reading Comp, Inference, and Necessary Assumption. Do we really have this specificity anywhere in the passage? We were told that scientists have figured out polarity for at least 51% of simple vertebrates? The only time we hear about "simple vertebrates", in paragraph 2, we hear that: A similar sperm-driven mechanism is thought to establish body orientation in some comparatively simple vertebrates such as frogs.

  3. Correct64% picked this

    Scientists will try to determine how polarity is established

    Why this is right

    This feels pretty strong on a first pass (scientists will try to determine?). It's pretty extreme to be so sure about the future. However, the end of the 2nd paragraph does say that, "How polarity is established in mammals is currently a tempting mystery to researchers". If an author thinks that X is a tempting mystery to researchers, then it's not a crazy rephrasing to think the author would agree that "some researchers will attempt to solve the mystery".

    Skill tested: Author Opinion · how this choice captures the passage's function is the move to repeat next time.

  4. Contradicted12% picked this

    Very few observations of embryonic development after polarity is established are generalizable to more than

    The final paragraph is saying the opposite of this. Very few observations of establishing polarity are generalizable. When it comes to the early stage of establishing polarity, species tend to vary widely. Yet for the later stages of development, once polarity is established, there are sets of "essential genes that are remarkably similar among all life forms for elaboration of parts" (such as building a pair of eyes).

  5. Unsupported Comparison Contradicted, if anything3% picked this

    Simpler organisms take longer to establish polarity than do more

    The passage never makes any broad comparison between the length of time that simple organisms take to establish polarity vs. the length of time that more complex organisms do. However, we have a simple organism like a fruit fly in which polarity is established before the egg is even fertilized, and we have more complex organisms like mammals in which many stages of cell division transpire before polarity is established. So from the tiny examples we do know, this comparison is backwards.

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