The Pan-American land bridge, or isthmus, connecting North and South

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

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

Yet the two oceans had
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

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?



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?

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

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:



Cheers!

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.

We can’t tell about the overall number of species as we don’t know how many species each region had before the migration.

Also, we don’t know about the extinction of any old / birth of any new species since the exchange, this answer can’t be correct.

B. The number of terrestrial animal species in South America today exceeds the number prior to the formation of the Pan-American isthmus.

We can’t tell about the overall number of species as we don’t know how many species each region had before the migration.

Also, we don’t know about the extinction of any old / birth of any new species since the exchange, this answer can’t be correct.

C. Of the indigenous North American species that migrated south across the Pan-American isthmus, more than three survive to this day.




The correct answer is C.

The second paragraph provides ample support for this inference. The author states that the terrestrial species migrating south were “better colonizers” than the ones migrating north, that more than half of those in the south today came from the north, and that only three animal species migrating north across the isthmus survive today. It is readily inferable, then, that more than three species that migrated south across the isthmus survive today.

D. Since the formation of the Pan-American isthmus, fewer terrestrial animals have traveled north across the isthmus than south.

We have the information about the number of animals that survived but not the number of animals that travelled. It may be that one million animals travelled and only three survided.

E. As the Pan-American isthmus began to form, most (avoid superlative … surely incorrect) pistol shrimp migrated west to what is now the Pacific Ocean.

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