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# The Pan-American land bridge, or isthmus, connecting

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The Pan-American land bridge, or isthmus, connecting [#permalink]

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08 Nov 2013, 03:23
6
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8
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BOOKMARKED
Question 1
00:00

Question Stats:

34% (01:35) correct 66% (01:30) wrong based on 119

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Question 2
00:00

Question Stats:

30% (00:48) correct 70% (00:54) wrong based on 113

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Question 3
00:00

Question Stats:

27% (01:05) correct 73% (01:03) wrong based on 100

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The Pan-American land bridge, or isthmus, connecting North
and South America was formed volcanically long after
dinosaurs became extinct. The isthmus cleaved populations of
marine organisms, creating sister species. These twin species,
called “geminates,” then evolved independently. Scientists
observe, for example, that Pacific pistol shrimp no longer mate
with those from the Atlantic Ocean. Yet the two oceans had
already begun to form their distinctive personalities long before
the is thmus was fully formed. As the seabed rose, Pacific
waters grew cooler, their up-swelling currents carrying rich
nutrients, while the Atlantic side grew shallower, warmer, and
nutrient poor. In fact, it was these new conditions, and not so
much the fully-formed isthmus, that spawned changes in the
shrimp population.

For terrestrial life, the impact of the isthmus was more
immediate. Animals traversed the newly formed bridge in both
directions, although North American creatures proved better
colonizers—more than half of South America’s mammals trace
direct lineage to this so-called Great American Biotic
Exchange. Only three animals—the armadillo, opossum, and
hedgehog—survive as transplants in the north today.

1. Which of the following statements finds the LEAST
support in the passage?

A. Population divergences resulting from the formation of the
Pan-American isthmus were more a process than an
event.
B. The divergence in ocean temperature during the formation
of the Pan-American isthmus resulted in a divergence in
the ocean’s nutrient value.
C. Genetic differences among pistol shrimp have grown to the
point that there are now at least two distinct species of
these shrimp.
D. The part of ocean which is now the Pacific grew deeper
due to the geologic forces that created the Pan-American
isthmus.
E. Not until the Pan-American isthmus was fully formed did
geminate marine organisms begin to develop in that area
of the ocean.

[Reveal] Spoiler:
D

2. Which of the following statements is most readily
inferable from the information in the passage?

A. Species of marine organisms in the Atlantic Ocean number
fewer today than before the formation of the Pan-American
isthmus.
B. The number of terrestrial animal species in South America
today exceeds the number prior to the formation of the
Pan-American isthmus.
C. Of the indigenous North American species that migrated
south across the Pan-American isthmus, more than three
survive to this day.
D. Since the formation of the Pan-American isthmus, fewer
terrestrial animals have traveled north across the isthmus
than south.
E. As the Pan-American isthmus began to form, most pistol
shrimp migrated west to what is now the Pacific Ocean.

[Reveal] Spoiler:
C

3. The author mentions the mating habits of pistol shrimp
in order to show that

A. Some species of marine organism inhabiting the Pacific Ocean
are now entirely distinct from those in the Atlantic Ocean.
B. Twin species of marine organisms can each survive even though
one species can no longer mate with the other.
C. Since the formation of the Pan-American isthmus, some marine
germinates no longer mate with their sister species.
D. Germinate species that do not mate with one another are
considered separate species.
E. The evolutionary impact of the Pan-American isthmus was
greater for marine organisms than for land animals.

[Reveal] Spoiler:
A

[Reveal] Spoiler: Question #1 OA
[Reveal] Spoiler: Question #2 OA
[Reveal] Spoiler: Question #3 OA

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Last edited by Juz2play on 03 Dec 2013, 23:29, edited 3 times in total.

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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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01 Dec 2013, 23:27
The second question buzzed me but on close second reading - I got it.

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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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13 Jan 2014, 04:49
8 minutes and got only 1 correct (3rd question) out of 3.

The 2nd question was very much in deep in the second paragraph.

Animals traversed the newly formed bridge in both directions, although North American creatures proved better colonizers—more than half of South America’s mammals trace direct lineage to this so-called Great American Biotic Exchange. Only three animals—the armadillo, opossum, and hedgehog—survive as transplants in the north today.

Since 3 animals (which migrated from south to north) survive in north today, the animals that migrated from north to south would have been more than 3 (because North American creatures proved better colonizers).

Can anyone help me explain the first question as I am still unable to understand it?
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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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13 Jan 2014, 05:42
1
KUDOS
First of all, we need just paragraph 1 to solve question 1.
(A) can be supported by "Yet the two oceans had already begun to form their distinctive personalities long before the is thmus was fully formed."
(B) can be supported by "As the seabed rose, Pacific waters grew cooler, their up-swelling currents carrying rich nutrients, while the Atlantic side grew shallower, warmer, and nutrient poor."
(C) can be supported by "The isthmus cleaved populations of marine organisms, creating sister species. These twin species, called “geminates,” then evolved independently. Scientists observe, for example, that Pacific pistol shrimp no longer mate with those from the Atlantic Ocean."
(E) can be supported by "The isthmus cleaved populations of marine organisms, creating sister species. These twin species, called “geminates,” then evolved independently."
So, (D) IS NOT SUPPORTED BY THE PASSAGE.
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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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14 Jan 2014, 10:11
sahilchaudhary wrote:
8 minutes and got only 1 correct (3rd question) out of 3.

The 2nd question was very much in deep in the second paragraph.

Animals traversed the newly formed bridge in both directions, although North American creatures proved better colonizers—more than half of South America’s mammals trace direct lineage to this so-called Great American Biotic Exchange. Only three animals—the armadillo, opossum, and hedgehog—survive as transplants in the north today.

Since 3 animals (which migrated from south to north) survive in north today, the animals that migrated from north to south would have been more than 3 (because North American creatures proved better colonizers).

Can anyone help me explain the first question as I am still unable to understand it?

when you see THE least means, in other words, that all choices but one must be true

Do you see D and its elements mentioned in the passage somowhere ?? NO. So D is out and therefore is the correct answer
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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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17 Feb 2014, 12:54
Got it as BCA. I am not very sure why B is wrong for the first question. There is no causality mentioned anywhere.

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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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17 Feb 2014, 20:44
I have doubts with first and third questions

For 1st I marked E and for 3rd I marked C

Q.11. Which of the following statements finds the LEAST
support in the passage?
A. Population divergences resulting from the formation of the
Pan-American isthmus were more a process than an
event.
B. The divergence in ocean temperature during the formation
of the Pan-American isthmus resulted in a divergence in
the ocean’s nutrient value.
C. Genetic differences among pistol shrimp have grown to the
point that there are now at least two distinct species of
these shrimp.
D. The part of ocean which is now the Pacific grew deeper
due to the geologic forces that created the Pan-American
isthmus.

here is support for D As the seabed rose, Pacific
waters grew cooler, their up-swelling currents carrying rich
nutrients, while the Atlantic side grew shallower, warmer, and
nutrient poor.

Atlantic grew shallower and pacific grew deeper

E. Not until the Pan-American isthmus was fully formed did
geminate marine organisms begin to develop in that area
of the ocean.

and opposite for E

already begun to form their distinctive personalities long before
the isthmus was fully formed.

So Geminate Organishms begin developing before isthmus was formed by process explained after this line .

for Q.3 . The author mentions the mating habits of pistol shrimp
in order to show that
A. Some species of marine organism inhabiting the Pacific Ocean
are now entirely distinct from those in the Atlantic Ocean.
B. Twin species of marine organisms can each survive even though
one species can no longer mate with the other.
C. Since the formation of the Pan-American isthmus, some marine
germinates no longer mate with their sister species.
D. Germinate species that do not mate with one another are
considered separate species.
E. The evolutionary impact of the Pan-American isthmus was
greater for marine organisms than for land animals.

The isthmus cleaved populations of
marine organisms, creating sister species. These twin species,
called “geminates,” then evolved independently.

The 2 species are not entirely different they are sister species , almost similar but do not mate.

C is what the authors intends to show.
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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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17 Feb 2014, 21:26
1
KUDOS
PUNEETSCHDV wrote:
I have doubts with first and third questions

For 1st I marked E and for 3rd I marked C

Q.11. Which of the following statements finds the LEAST
support in the passage?
A. Population divergences resulting from the formation of the
Pan-American isthmus were more a process than an
event.
B. The divergence in ocean temperature during the formation
of the Pan-American isthmus resulted in a divergence in
the ocean’s nutrient value.
C. Genetic differences among pistol shrimp have grown to the
point that there are now at least two distinct species of
these shrimp.
D. The part of ocean which is now the Pacific grew deeper
due to the geologic forces that created the Pan-American
isthmus.

here is support for D As the seabed rose, Pacific
waters grew cooler, their up-swelling currents carrying rich
nutrients, while the Atlantic side grew shallower, warmer, and
nutrient poor.

Atlantic grew shallower and pacific grew deeper

E. Not until the Pan-American isthmus was fully formed did
geminate marine organisms begin to develop in that area
of the ocean.

and opposite for E

already begun to form their distinctive personalities long before
the isthmus was fully formed.

So Geminate Organishms begin developing before isthmus was formed by process explained after this line .

for Q.3 . The author mentions the mating habits of pistol shrimp
in order to show that
A. Some species of marine organism inhabiting the Pacific Ocean
are now entirely distinct from those in the Atlantic Ocean.
B. Twin species of marine organisms can each survive even though
one species can no longer mate with the other.
C. Since the formation of the Pan-American isthmus, some marine
germinates no longer mate with their sister species.
D. Germinate species that do not mate with one another are
considered separate species.
E. The evolutionary impact of the Pan-American isthmus was
greater for marine organisms than for land animals.

The isthmus cleaved populations of
marine organisms, creating sister species. These twin species,
called “geminates,” then evolved independently.

The 2 species are not entirely different they are sister species , almost similar but do not mate.

C is what the authors intends to show.

For the first question, the option E has support in the passage. Please refer to the below sentences from the Paragraph 1.

The isthmus cleaved populations of
marine organisms, creating sister species. These twin species,
called “geminates,” then evolved independently.

Option E is specific to 'geminates', and from the above sentences 'geminates' evolved only after the formation of the isthmus.

For the third question, please read the below sentences from Paragraph 1.

These twin species,
called “geminates,” then evolved independently. Scientists
observe, for example, that Pacific pistol shrimp no longer mate
with those from the Atlantic Ocean.

Mating of Pistol shrimp is mentioned as an example in the passage. What is this example for? This is an example for the aforementioned behavior that twin species evolved independently (without mating).

Option C is true, but it is not the point why the author mentions mating of the pistol shrimp

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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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17 Feb 2014, 21:42
Quote:
1. Which of the following statements finds the LEAST
support in the passage?

B. The divergence in ocean temperature during the formation
of the Pan-American isthmus resulted in a divergence in
the ocean’s nutrient value.

I thought the answer is B for the first question because I didn't see any form of causality in the below sentences from Paragraph 1. The answer option mentions 'resulted' indicating causation. But, when I re-read the sentences carefully, I got a doubt if I am missing something here.

Can you guys help me interpret the below sentence?

Quote:
As the seabed rose, Pacific
waters grew cooler, their up-swelling currents carrying rich
nutrients, while the Atlantic side grew shallower, warmer, and
nutrient poor.

In the above sentence, what is the role of 'their up-swelling currents carrying rich nutrients' ?

In my view, it is a modifier modifying the clause 'Pacific waters grew cooler'.
So, it makes a meaning that it is the up-swelling currents carrying rich nutrients that made the Pacific waters cooler.

But, this meaning is still the opposite of B.

Can somebody help me understand how you found support for option B?

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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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18 Feb 2014, 04:20
1. Which of the following statements finds the LEAST
support in the passage?
A. Population divergences resulting from the formation of the
Pan-American isthmus were more a process than an
event. --- The first para is talking compltely about this. As we can see, there were changes in nutrient, temperature and everything mentioned in para. Note that isthmus didn't form by that time. Everything after the line - Yet.... are useful to evaluate this.
Eliminate A

B. The divergence in ocean temperature during the formation
of the Pan-American isthmus resulted in a divergence in
the ocean’s nutrient value. --- As the seabed rose, Pacific
waters grew cooler, their up-swelling currents carrying rich
nutrients,
Eliminate B

C. Genetic differences among pistol shrimp have grown to the
point that there are now at least two distinct species of
these shrimp. --- The isthmus cleaved populations of
marine organisms, creating sister species. These twin species,....
...that Pacific pistol shrimp no longer mate
with those from the Atlantic Ocean...
Eliminate C

D. The part of ocean which is now the Pacific grew deeper
due to the geologic forces that created the Pan-American
isthmus. --- wait a minute.. As the seabed rose, Pacific
waters grew cooler, their up-swelling currents

E. Not until the Pan-American isthmus was fully formed did
geminate marine organisms begin to develop in that area
of the ocean. ---
The isthmus cleaved populations of
marine organisms, creating sister species

In fact, it was these new conditions, and not so
much the fully-formed isthmus, that spawned changes in the
shrimp population
Eliminate E

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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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15 Apr 2017, 23:02
Could any expert please explain how the answer of third question is A
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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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15 Apr 2017, 23:53
daboo343 wrote:
Could any expert please explain how the answer of third question is A

Hey Daboo,

I have quoted below (and underlined relevant portions) a suitable response from the previous replies (gmatter0913). Please do go through it (once more if you have already), and let me know if you are not clear with respect to any particular portion:

Quote:
For the third question, please read the below sentences from Paragraph 1.

These twin species, called “geminates,” then evolved independently. Scientists
observe, for example, that Pacific pistol shrimp no longer mate
with those from the Atlantic Ocean.

Mating of Pistol shrimp is mentioned as an example in the passage. What is this example for? This is an example for the aforementioned behavior that twin species evolved independently (without mating).

Cheers!

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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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18 Apr 2017, 11:40
i got all three wrong a tough passage for me!

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Re: The Pan-American land bridge, or isthmus, connecting [#permalink]

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18 Apr 2017, 21:12
goforgmat wrote:
i got all three wrong a tough passage for me!

Hi Please point out, if you did not understand any specific thing out of this passage.. Happy to help..

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Re: The Pan-American land bridge, or isthmus, connecting   [#permalink] 18 Apr 2017, 21:12
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