The first thing any embryo must do before it can develop into

Question

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
  (5)   mechanisms that establish the earliest spatial
configurations in an embryo are far less similar across
life forms than those relied on for later development,
as in the formation of limbs or a nervous system: for
example, the signals that the developing fruit fly uses
  (10)   to know its front end from its back end turn out to be
radically different from those that the nematode, a
type of worm, relies on, and both appear to be quite
different from the polarity signals in the development
of humans and other mammals.

(15)   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
  (20)   distributed throughout the cell, it takes a fruit fly a
week to make an egg, but once that well-appointed
egg is fertilized, it is transformed from a single cell
into a crawling larva in a day. By contrast, in the
embryonic development of certain nematodes, the
  (25)   point where the sperm enters the egg appears to
provide crucial positional information. Once that
information is present, little bundles of proteins called
p-granules, initially distributed uniformly throughout
the cytoplasm, begin to congregate at one end of the
  (30)   yolk; when the fertilized egg divides, one of the
resulting cells gets all the p-granules. The presence or
absence of these granules in cells appears to help
determine whether their subsequent divisions will
lead to the formation of the worm’s front or back
  (35)   half. A similar sperm-driven mechanism is also
thought to establish body orientation in some
comparatively simple vertebrates such as frogs,
though apparently not in more complex vertebrates
such as mammals. Research indicates that in human
  (40)   and other mammalian embryos, polarity develops
much later, as many stages of cell division occur with
no apparent asymmetries among cells. Yet how
polarity is established in mammals is currently a
tempting mystery to researchers.

(45)   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
  (50)   are similar to the genes that make eyes in mice or
humans. So a seeming paradox arises: when embryos
of different species are at the one- or few-cell stage
and still appear almost identical, the mechanisms of
development they use are vastly different; yet when
  (55)   they start growing brains or extremities and become
identifiable as distinct species, the developmental
mechanisms they use are remarkably similar.    1 
 1. Which one of the following most accurately expresses the main point of the passage?

(A) Species differ more in the mechanisms that determine the spatial orientation in an embryo than they do in their overall genetic makeup.
(B) Embryos determine their front from their back and top from bottom by different methods, depending on whether the organism is simple or more complex.
(C) While very similar genes help determine the later embryonic development of all organisms, the genetic mechanisms by which embryos establish early polarity vary dramatically from one organism to the next.
(D) The mechanisms by which embryos establish early polarity differ depending on whether the signals by which polarity is achieved are inscribed in the cytoplasm of the egg or the p-granules of the sperm.
(E) Despite their apparent dissimilarity from species to species, the means by which organisms establish polarity rely on essentially the same genetic mechanisms.

2 
 2. The passage suggests that the author would be most likely to agree with which one of the following statements?

(A) The simpler the organism, the greater the speed at which it develops from fertilized egg to embryo.
(B) Scientists have determined how polarity is established in most simple vertebrates.
(C) Scientists will try to determine how polarity is established in humans.
(D) Very few observations of embryonic development after polarity is established are generalizable to more than a single species.
(E) Simpler organisms take longer to establish polarity than do more complex organisms.

3 
 3. The passage provides information to suggest that which one of the following relationships exists between the development of humans and the development of fruit flies?

(A) Since humans and fruit flies use similar genetic material in their development, analogies from fruit fly behavior can be useful in explaining human behavior.
(B) For the elaboration of parts, human development relies on genetic material quite different in nature, though not in quantity, from that of a fruit fly.
(C) Positional information for establishing polarity in a human embryo, as in that of the fruit fly, is distributed throughout the egg prior to fertilization.
(D) A study of the development of the fruit fly’s visual system would more likely be applicable to questions of human development than would a study of the mechanisms that establish the fruit fly’s polarity.
(E) While the fruit fly egg becomes a larva in a single day, a human embryo takes significantly longer to develop because humans cannot develop limbs until they have established a nervous system.

4 
 4. According to the passage, polarity is established in a human embryo

(A) after more stages of cell division than in frogs
(B) before the sperm enters the egg
(C) after positional information is provided by the massing of p-granules
(D) by the same sperm-driven mechanism as in the nematode
(E) in the same way as in simpler vertebrates

5 
 5. By “conservation of mechanism” (line 48) the author is probably referring to

(A) how the same mechanism can be used to form different parts of the same organism
(B) the fact that no genetic material is wasted in development
(C) how few genes a given organism requires in order to elaborate its parts
(D) a highly complex organism’s requiring no more genetic material than a simpler one
(E) the fact that analogous structures in different species are brought about by similar genetic means

6 
 6. Which one of the following most accurately states the main purpose of the second paragraph?

(A) to illustrate the diversity of processes by which organisms establish early polarity
(B) to elaborate on the differences between embryonic formation in the fruit fly and in the nematode
(C) to suggest why the process of establishing early polarity in humans is not yet understood
(D) to demonstrate the significance and necessity for genetic development of establishing polarity
(E) to demonstrate that there are two main types of mechanism by which early polarity is established

7 
 7. According to the passage, which one of the following is a major difference between the establishment of polarity in the fruit fly and in the nematode?

(A) The fruit fly embryo takes longer to establish polarity than does the nematode embryo.
(B) The mechanisms that establish polarity are more easily identifiable in the nematode than in the fruit fly.
(C) Polarity signals for the fruit fly embryo are inscribed entirely in the egg and these signals for the nematode embryo are inscribed entirely in the sperm.
(D) Polarity in the fruit fly takes more stages of cell division to become established than in the nematode.
(E) Polarity is established for the fruit fly before fertilization and for the nematode through fertilization.

8 
 8. The author’s primary purpose in the passage is to

(A) articulate a theory of how early polarity is established and support the theory by an analysis of data
(B) describe a phase in the development of organisms in which the genetic mechanisms used are disparate and discuss why this disparity is surprising
(C) provide a classification of the mechanisms by which different life forms establish early polarity
(D) argue that a certain genetic process must occur in all life forms, regardless of their apparent dissimilarity
(E) explain why an embryo must establish early polarity before it can develop into an organism

Sajjad1994 · Answer

Explanation

1. Which one of the following most accurately expresses the main point of the passage?

Explanation

This question and question #8 are both Globals, which are best answered immediately after you finish the passage. Here, the Main Idea must pick up on the author’s neutral tone, but it also must connect the different elements of the passage. Those different elements are the mechanisms for developing polarity, and the mechanisms for development once polarity has been established. Only  (C)  encompasses the scope of the entire passage with the appropriate tone.

(A)  distorts the paradox in  paragraph 3 ; species are similar in the sets of genes that allow them to develop once polarity is established, not in their overall genetic makeup.

(B)  is a real Train Wreck—it uses a detail from paragraph 1, but adds an out-of-scope connection between the method of determining polarity and the complexity of the organism, and fails to mention paragraph 3’s paradox.

(D)  makes Faulty Use of a Detail from  paragraph 2.

(E)  reverses the essential paradox. The similar genetic mechanisms are used after polarity is established, not to establish it in the first place.

Answer: C

8. The author’s primary purpose in the passage is to

Explanation

Even though this question was the last one in the passage, it would have been easiest to answer immediately after finishing the passage. This is when you’re still thinking about the passage as a whole, which helps you eliminate wrong answer choices that are too focused on the details. A quick scan of the initial verbs in each choice will help us eliminate many of the choices in this question. Only  (B)  matches the author’s neutral tone and includes the entire scope of the passage.

(A)  The author does not  “articulate a theory.”  Instead, she discusses the different mechanisms for establishing polarity and the paradox that arises from them.

(C) “Provide a classification”  captures the author’s neutral tone, but ignores paragraph 3’s discussion of embryonic development after polarity is established.

(D) “Argue”  is too harsh a tone for this neutral passage.

(E)  The author never tries to  “explain why an embryo must establish early polarity,”  but takes this idea for granted and discusses how polarity is established.

Answer: B

glagad · Answer

GMATNinja   MartyMurray   Sajjad1994  - This got to be a very difficult passage for me with least accuracy and least comprehension despite following the key techniques for RCs.

My question is, is this a passage to be worried about since I am taking GMAT and this is an LSAT passage?
I don't want to over-spend time on GMAT prep right now.

GMATNinja · Answer

It's worth remembering that you don't need to be perfect to get a great score on the GMAT. It's remarkably common to miss 8-10 questions and still score in the low 80s on the verbal section. Even students scoring in the mid-80s are likely to miss several questions.

The last thing you want to do on the GMAT is let the questions that are hardest for you take up all of your time and energy. So if you're feeling pretty good about ~80% of the LSAT passages you see -- but you get slapped in the face by a passage here and there -- you're probably doing just fine. If you're scoring close to your target on official GMAT practice exams, you're in good shape -- don't stress about the gnarliest LSAT passages.

siddhantvarma · Answer

7. According to the passage, which one of the following is a major difference between the establishment of polarity in the fruit fly and in the nematode?

Let's take a look at answer choice C:

(C) Polarity signals for the fruit fly embryo are inscribed entirely in the egg and these signals for the nematode embryo are inscribed entirely in the sperm.

We know that while polarity signals in fruit flies are inscribed in the egg (lines 15-17), the passage does not state that polarity signals in nematodes are inscribed entirely in the sperm.
 
Instead, the sperm provides crucial positional information, and the p-granules within the egg play a key role in establishing polarity (lines 25-30).
 
Hope that helps! Let me know if you need further clarification.

egmat · Answer

Question Type: Author Agreement/Inference

Question stem:  "The passage suggests that the author would be most likely to agree with which one of the following statements?"

What This Question Type Demands:

This is an  inference question  asking for what the author would agree with based on passage content. Key requirements:

1.  Must be supported by passage evidence  - not just plausible speculation
2.  Author's perspective  - what the author believes/would believe, not what others think
3.  "Suggests"  - can be implied, but must be a necessary/logical inference
4.  "Most likely"  - we need the BEST supported option, even if multiple seem reasonable

Critical Strategy: 
- Look for direct statements or clear logical implications
- Avoid answers that go beyond passage scope
- Avoid answers that contradict passage language (certainty vs. uncertainty)
- The correct answer often connects to the author's explicit commentary or conclusions

ANSWER CHOICE ANALYSIS

(A) ❌ "The simpler the organism, the greater the speed at which it develops from fertilized egg to embryo."

Passage Evidence: 
- Lines 20-23: Fruit fly makes egg in a week, but "once that well-appointed egg is fertilized, it is transformed from a single cell into a crawling larva in a day"
- Lines 24-35: Nematode development described, but  no timeline given 
- Lines 39-42: Mammalian embryos have "many stages of cell division" before polarity established

Analysis: 
- We have ONE example of fast development (fruit fly: 1 day from fertilization to larva)
- We have ZERO comparative data for nematodes
- We have VAGUE information for mammals (many stages, but no timeframe)
- The passage discusses polarity establishment timing, NOT overall development speed

Fatal Flaw:  This overgeneralizes from a single data point. The passage provides  no systematic comparison  of development speeds across different organism complexities. The fruit fly example shows speed AFTER fertilization, but the passage emphasizes it takes a week to MAKE the egg - so total process isn't necessarily faster.

Verdict: ❌ UNSUPPORTED  - extrapolates beyond evidence

(B) ❌ "Scientists have determined how polarity is established in most simple vertebrates."

Passage Evidence: 
- Lines 35-39: "A similar sperm-driven mechanism is  also thought to  establish body orientation in  some  comparatively simple vertebrates such as frogs, though apparently not in more complex vertebrates such as mammals."

Analysis - Word by Word:

"thought to"  = hypothesis/theory, NOT determination/proven fact
- This signals  UNCERTAINTY , not established knowledge
- Scientists think this might be how it works, but haven't definitively determined it

"some" ≠ "most" 
- "Some simple vertebrates" is explicitly  LIMITED scope 
- "Most simple vertebrates" would require evidence about the majority
- The passage gives ONE example: frogs

Fatal Flaw:  The answer choice claims  CERTAINTY  ("determined") where passage shows  UNCERTAINTY  ("thought to"), and claims  BREADTH  ("most") where passage shows  LIMITATION  ("some").

Verdict: ❌ WRONG  - contradicts passage's language of uncertainty and limited scope

(C) ✅ "Scientists will try to determine how polarity is established in humans."

Passage Evidence: 
- Lines 39-44: "Research indicates that in human and other mammalian embryos, polarity develops much later, as many stages of cell division occur with no apparent asymmetries among cells. Yet  how polarity is established in mammals is currently a tempting mystery to researchers. "

Analysis:

"tempting mystery"  = something that attracts/draws interest
 "to researchers"  = specifically to scientists who investigate such questions

Logical Chain: 
1. EXPLICIT: The mechanism is unknown ("mystery")
2. EXPLICIT: It attracts researchers ("tempting")
3. IMPLIED: What do researchers do with tempting mysteries? They investigate them
4. CONCLUSION: Scientists will try to determine how this works

Why This Must Be True: 
- The author wouldn't call something "tempting to researchers" if believing researchers won't pursue it
- That would be contradictory - like saying "this dessert is tempting to hungry people who won't try to eat it"
- The phrase "tempting mystery to researchers"  NECESSARILY implies future investigation attempts

Strength of Support:  STRONG - directly follows from author's explicit characterization

Verdict: ✅ CORRECT  - logically necessary inference from explicit statement

(D) ❌ "Very few observations of embryonic development after polarity is established are generalizable to more than a single species."

Passage Evidence: 
- Lines 45-51: "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 mice or humans."

Analysis:

This is the  OPPOSITE  of what the passage says.

The passage explicitly states: 
- Mechanisms AFTER polarity are "remarkably similar among all life forms"
- There is "astonishing conservation of mechanism"
- Eye-formation genes are similar across flies, mice, and humans

"Very few observations... generalizable"  directly contradicts  "remarkably similar among all life forms"

Fatal Flaw:  This reverses the passage's main point about post-polarity development. The entire thrust of lines 45-55 is that  MANY observations  about post-polarity development  ARE generalizable  across species - that's what makes it "astonishing" and creates the "paradox."

Verdict: ❌ WRONG  - directly contradicts passage

(E) ❌ "Simpler organisms take longer to establish polarity than do more complex organisms."

Passage Evidence: 
- Lines 15-23: Fruit fly - polarity established BEFORE fertilization (during egg formation, takes a week)
- Lines 24-35: Nematode - polarity begins establishing when sperm enters, then p-granules congregate
- Lines 39-44: Mammals - polarity develops "much later" after "many stages of cell division"

Analysis:

Timeline comparison: 
- Fruit fly: Polarity pre-set during egg formation
- Nematode: Polarity begins at fertilization and develops during early divisions
- Mammals: Polarity develops after many cell divisions ("much later")

The passage indicates:  More complex organisms (mammals) take  LONGER  to establish polarity than simpler ones (fruit fly has it ready immediately at fertilization).

Fatal Flaw:  This gets the relationship  BACKWARDS . The passage suggests mammals (complex) take longer than fruit flies (simple), not the reverse.

Verdict: ❌ WRONG  - reverses the relationship shown in passage

SUMMARY

Answer Choice Breakdown:

(A) ❌  Overgeneralizes from insufficient data

(B) ❌  Changes "thought to" → "determined" and "some" → "most"

(C) ✅ CORRECT  Logical necessity from "tempting mystery to researchers"

(D) ❌  Directly contradicts "remarkably similar among all life forms"

(E) ❌  Reverses the actual relationship described

Only (C)  is a necessary logical inference that the author must agree with based on explicit passage content.

The first thing any embryo must do before it can develop into

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The first thing any embryo must do before it can develop into

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