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# The two claws of the mature American lobster are decidedly different f

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The two claws of the mature American lobster are decidedly different f  [#permalink]

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Updated on: 25 Jan 2020, 05:14
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1994 02 SECTION B 21-27

The two claws of the mature American lobster are decidedly different from each other. The crusher claw is short and stout; the cutter claw is long and slender. Such bilateral asymmetry, in which the right side of the body is, in all other respects, a mirror image of the left side, is not unlike handedness in humans. But where the majority of humans are right-handed, in lobsters the crusher claw appears with equal probability on either the right or left side of the body.

Bilateral asymmetry of the claws comes about gradually. In the juvenile fourth and fifth stages of development, the paired claws are symmetrical and cutterlike. Asymmetry begins to appear in the juvenile sixth stage of development, and the paired claws further diverge toward well-defined cutter and crusher claws during succeeding stages. An intriguing aspect of this development was discovered by Victor Emmel. He found that if one of the paired claws is removed during the fourth or fifth stage, the intact claw invariably becomes a crusher, while the regenerated claw becomes a cutter. Removal of a claw during a later juvenile stage or during adulthood, when asymmetry is present, does not alter the asymmetry; the intact and the regenerate claws retain their original structures.

These observations indicate that the conditions that trigger differentiation must operate in a random manner when the paired claws are intact but in a nonrandom manner when one of the claws is lost. One possible explanation is that differential use of the claws determines their asymmetry. Perhaps the claw that is used more becomes the crusher. This would explain why, when one of the claws is missing during the fourth or fifth stage, the intact claw always becomes a crusher. With two intact claws, initial use of one claw might prompt the animal to use it more than the other throughout the juvenile fourth and fifth stages, causing it to become a crusher.

To test this hypothesis, researchers raised lobsters in the juvenile fourth and fifth stages of development in a laboratory environment in which the lobsters could manipulate oyster chips. (Not coincidentally, at this stage of development lobsters typically change from a habitat where they drift passively, to the ocean floor where they have the opportunity to be more active by burrowing in the substrate.) Under these conditions, the lobsters developed asymmetric claws, half with crusher claws on the left, and half with crusher claws on the right. In contrast, when juvenile lobsters were reared in a smooth tank without the oyster chips, the majority developed two cutter claws. This unusual configuration of symmetrical cutter claws did not change when the lobsters were subsequently placed in a manipulatable environment or when they lost and regenerated one or both claws.

1. ​The passage is primarily concerned with

(A) drawing an analogy between asymmetry in lobsters and handedness in humans
(B) developing a method for predicting whether crusher claws in lobsters will appear on the left or right side
(C) explaining differences between lobsters’ crusher claws and cutter claws
(D) discussing a possible explanation for the way bilateral asymmetry is determined in lobsters
(E) summarizing the stages of development of the lobster

2. Each of the following statements about the development of a lobster’s crusher claw is supported by information in the passage EXCEPT:

(A) It can be stopped on one side and begun on the other after the juvenile sixth stage.
(B) It occurs gradually over a number of stages.
(C) It is initially apparent in the juvenile sixth stage.
(D) It can occur even when a prospective crusher claw is removed in the juvenile sixth stage.
(E) It is less likely in the absence of a manipulatable environment.

3. Which of the following experimental results, if observed, would most clearly contradict the findings of Victor Emmel?

(A) A left cutterlike claw is removed in the fifth stage and a crusher claw develops on the right side.
(B) A left cutterlike claw is removed in the fourth stage and a crusher claw develops on the left side.
(C) A left cutterlike claw is removed in the sixth stage and a crusher claw develops on the right side.
(D) Both cutterlike claws are removed in the fifth stage and a crusher claw develops on the left side.
(E) Both cutterlike claws are removed in the fourth stage and a crusher claw develops on the right side.

4. ​It can be inferred that of the two laboratory environments mentioned in the passage, the one with oyster chips was designed to

(A) prove that the presence of oyster chips was not necessary for the development of a crusher claw
(B) prove that the relative length of time that the lobsters were exposed to the oyster-chip environment had little impact on the development of a crusher claw
(C) eliminate the environment as a possible influence in the development of a crusher claw
(D) control on which side the crusher claw develops
(E) simulate the conditions that lobsters encounter in their natural environmen

5. ​​​It can be inferred from the passage that one difference between lobsters in the earlier stages of development and those in the juvenile fourth and fifth stages is that lobsters in the early stages are

(A) likely to be less active
(B) likely to be less symmetrical
(C) more likely to lose a claw
(D) more likely to replace a crusher claw with a cutter claw
(E) more likely to regenerate a lost claw

6. ​​Which of the following conditions does the passage suggest is a possible cause for the failure of a lobster to develop a crusher claw?

(A) The loss of a claw during the third or earlier stage of development
(B) The loss of a claw during the fourth or fifth stage of development
(C) The loss of a claw during the sixth stage of development
(D) Development in an environment devoid of material that can be manipulated
(E) Development in an environment that changes frequently throughout the stages of development

7. ​​​The author regards the idea that differentiation is triggered randomly when paired claws remain intact as

(A) irrefutable considering the authoritative nature of Emmel’s observations
(B) likely in view of present evidence
(C) contradictory to conventional thinking on lobster-claw differentiation
(D) purely speculative because it is based on scattered research and experimentation
(E) unlikely because of apparent inconsistencies with theories on handedness in humans

Originally posted by pathy on 17 Jan 2020, 19:39.
Last edited by pathy on 25 Jan 2020, 05:14, edited 5 times in total.
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Joined: 31 Jan 2019
Posts: 362
Location: Switzerland
Concentration: General Management
GPA: 3.9
Re: The two claws of the mature American lobster are decidedly different f  [#permalink]

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31 Jan 2020, 05:01
Hi everyone,
Got 6/7 correct in 16:40 minutes, including 5:50 minutes to read.

--------------------------------------------------------------------------------------------

P1

In paragraph one we are given that the American lobster can have 2 kind of claws, their description, a comparison with relation to humans and the fact that such lobsters can have either of the two claws on the right or left side of their body.

Purpose: To present the claws of the American lobster.

P2

Here we are given that the asymmetry starts at the 6th stage of development of the American lobster. Plus the author tells us that VE found out that if a claw is removed before the 6th stage and after the 3rd stage, that claw will always become a cutter like claw and the other a crusher claw.

Purpose: The purpose of this paragraph is to describe the development of asymmetry and highlight an interesting discovery.

P3

Here the author points out that when a claw is removed we certainly know the outcome, but when a claw is not removed we don't. An explanation is given: maybe the claw that is used more frequently becomes a crusher.

Purpose: The purpose of this paragraph is to present a possible explanation for the seemingly rather rate of differentiation among the American lobsters

P4

Here we are presented with an experimented intended to test the validity of the explanation presented in P3. Apparently if lobsters use their claws, they develop randomly a crusher claw but if they don't use their claws, the majority develops 2 cutter claws.

Purpose: The purpose of this paragraph is to test the validity of the explanation previously presented.

Main point

The main point is to understand why American lobsters develop a crusher or a cutter claw in a seemingly random way.

--------------------------------------------------------------------------------------------

1. ​The passage is primarily concerned with

Pre-thinking

Main point question

The main point is to understand why American lobsters develop a crusher or a cutter claw in a seemingly random way.

(A) drawing an analogy between asymmetry in lobsters and handedness in humans
partial scope

(B) developing a method for predicting whether crusher claws in lobsters will appear on the left or right side
out of scope

(C) explaining differences between lobsters’ crusher claws and cutter claws
partial scope

(D) discussing a possible explanation for the way bilateral asymmetry is determined in lobsters
In line with pre-thinking

(E) summarizing the stages of development of the lobster
partial scope

--------------------------------------------------------------------------------------------

2. Each of the following statements about the development of a lobster’s crusher claw is supported by information in the passage EXCEPT:

Pre-thinking

Detail question

Let's evaluate each option

(A) It can be stopped on one side and begun on the other after the juvenile sixth stage.
The passage clearly states that after the 6th stage this scenario cannot occur

(B) It occurs gradually over a number of stages.
Supported

(C) It is initially apparent in the juvenile sixth stage.
supported

(D) It can occur even when a prospective crusher claw is removed in the juvenile sixth stage.
Yes, supported

(E) It is less likely in the absence of a manipulatable environment.
supported in the last paragraph

--------------------------------------------------------------------------------------------

3. Which of the following experimental results, if observed, would most clearly contradict the findings of Victor Emmel?

Pre-thinking

Weaken question

VE discovered an interesting finding about the claws. When one claw is cut during the 4th/5th stage of development, that claw becomes a cutter and the there a crusher.

(A) A left cutterlike claw is removed in the fifth stage and a crusher claw develops on the right side.
Strengthener

(B) A left cutterlike claw is removed in the fourth stage and a crusher claw develops on the left side.
Weakener

(C) A left cutterlike claw is removed in the sixth stage and a crusher claw develops on the right side.
Could happen

(D) Both cutterlike claws are removed in the fifth stage and a crusher claw develops on the left side.
could happen

(E) Both cutterlike claws are removed in the fourth stage and a crusher claw develops on the right side.
Could happen

--------------------------------------------------------------------------------------------

4. ​It can be inferred that of the two laboratory environments mentioned in the passage, the one with oyster chips was designed to

Pre-thinking

Inference/Function question

From the last paragraph: "Not coincidentally, at this stage of development lobsters typically change from a habitat where they drift passively, to the ocean floor where they have the opportunity to be more active by burrowing in the substrate."

(A) prove that the presence of oyster chips was not necessary for the development of a crusher claw
Not in line with pre-thinking

(B) prove that the relative length of time that the lobsters were exposed to the oyster-chip environment had little impact on the development of a crusher claw
Not in line with pre-thinking

(C) eliminate the environment as a possible influence in the development of a crusher claw
Not in line with pre-thinking

(D) control on which side the crusher claw develops
Not in line with pre-thinking

(E) simulate the conditions that lobsters encounter in their natural environmen
in line with pre-thinking

--------------------------------------------------------------------------------------------

5. ​​​It can be inferred from the passage that one difference between lobsters in the earlier stages of development and those in the juvenile fourth and fifth stages is that lobsters in the early stages are

Pre-thinking

Inference question

From the last paragraph: "Not coincidentally, at this stage of development lobsters typically change from a habitat where they drift passively, to the ocean floor where they have the opportunity to be more active by burrowing in the substrate."

(A) likely to be less active
[b]in line with pre-thinking[/b]

(B) likely to be less symmetrical
Not in line with pre-thinking

(C) more likely to lose a claw
Not in line with pre-thinking

(D) more likely to replace a crusher claw with a cutter claw
Not in line with pre-thinking

(E) more likely to regenerate a lost claw
Not in line with pre-thinking

--------------------------------------------------------------------------------------------

6. ​​Which of the following conditions does the passage suggest is a possible cause for the failure of a lobster to develop a crusher claw?

Pre-thinking

Inference question

There are different possibilities: the lobster does not use his claw a lot; the lobster loses the cutter claw after the 6th stage....

(A) The loss of a claw during the third or earlier stage of development
we don't know that

(B) The loss of a claw during the fourth or fifth stage of development
Cannot be inferred

(C) The loss of a claw during the sixth stage of development
cannot be inferred

(D) Development in an environment devoid of material that can be manipulated
in line with what the experiment done in the last paragraph proves

(E) Development in an environment that changes frequently throughout the stages of development
cannot be inferred

--------------------------------------------------------------------------------------------

7. ​​​The author regards the idea that differentiation is triggered randomly when paired claws remain intact as

Pre-thinking

Detail question

The author seems to believe such theory

(A) irrefutable considering the authoritative nature of Emmel’s observations
Not in line with pre-thinking

(B) likely in view of present evidence
in line with pre-thinking

(C) contradictory to conventional thinking on lobster-claw differentiation
Not in line with pre-thinking

(D) purely speculative because it is based on scattered research and experimentation
Not in line with pre-thinking

(E) unlikely because of apparent inconsistencies with theories on handedness in humans
Not in line with pre-thinking

--------------------------------------------------------------------------------------------

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Re: The two claws of the mature American lobster are decidedly different f  [#permalink]

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31 Jan 2020, 09:24
All correct in 14 mins 50 seconds, including 5mins 30 seconds to read
Para 1- bilateral asymmetry in American lobster
Para 2- Asymmetry begins to appear in the juvenile sixth stage of development; Victor Emmel's discovery
Para 3- inferences based on VE's discovery; explanation
Para 4- Testing of hypothesis

1. ​The passage is primarily concerned with
(D) discussing a possible explanation for the way bilateral asymmetry is determined in lobsters- Correct

2. Each of the following statements about the development of a lobster’s crusher claw is supported by information in the passage EXCEPT:
(A) It can be stopped on one side and begun on the other after the juvenile sixth stage.- Correct
(B) It occurs gradually over a number of stages.- incorrect; Asymmetry begins to appear in the juvenile sixth stage of development, and the paired claws further diverge toward well-defined cutter and crusher claws during succeeding stages.
(C) It is initially apparent in the juvenile sixth stage.- - incorrect; Asymmetry begins to appear in the juvenile sixth stage of development, and the paired claws further diverge toward well-defined cutter and crusher claws during succeeding stages.
(D) It can occur even when a prospective crusher claw is removed in the juvenile sixth stage.- incorrect, if one of the paired claws is removed during the fourth or fifth stage, the intact claw invariably becomes a crusher, while the regenerated claw becomes a cutter.
(E) It is less likely in the absence of a manipulatable environment.- incorrect; In contrast, when juvenile lobsters were reared in a smooth tank without the oyster chips, the majority developed two cutter claws.

3. Which of the following experimental results, if observed, would most clearly contradict the findings of Victor Emmel?
(B) A left cutterlike claw is removed in the fourth stage and a crusher claw develops on the left side.- Correct; this is opposite of VE's discovery
He found that if one of the paired claws is removed during the fourth or fifth stage, the intact claw invariably becomes a crusher, while the regenerated claw becomes a cutter.

4. ​It can be inferred that of the two laboratory environments mentioned in the passage, the one with oyster chips was designed to
(E) simulate the conditions that lobsters encounter in their natural environment
To test this hypothesis, researchers raised lobsters in the juvenile fourth and fifth stages of development in a laboratory environment in which the lobsters could manipulate oyster chips. (Not coincidentally, at this stage of development lobsters typically change from a habitat where they drift passively, to the ocean floor where they have the opportunity to be more active by burrowing in the substrate.)

5. ​​​It can be inferred from the passage that one difference between lobsters in the earlier stages of development and those in the juvenile fourth and fifth stages is that lobsters in the early stages are
(A) likely to be less active
Not coincidentally, at this stage of development lobsters typically change from a habitat where they drift passively, to the ocean floor where they have the opportunity to be more active by burrowing in the substrate

6. ​​Which of the following conditions does the passage suggest is a possible cause for the failure of a lobster to develop a crusher claw?
(D) Development in an environment devoid of material that can be manipulated
Under these conditions, the lobsters developed asymmetric claws, half with crusher claws on the left, and half with crusher claws on the right. In contrast, when juvenile lobsters were reared in a smooth tank without the oyster chips, the majority developed two cutter claws.

7. ​​​The author regards the idea that differentiation is triggered randomly when paired claws remain intact as
(B) likely in view of present evidence

These observations indicate that the conditions that trigger differentiation must operate in a random manner when the paired claws are intact but in a nonrandom manner when one of the claws is lost.
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Re: The two claws of the mature American lobster are decidedly different f   [#permalink] 31 Jan 2020, 09:24
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