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605-655 Level|   Non-Math Related|               
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Cause: An increase in phytoplankton so that sea star population increased

Effect: An increase in crown-of-thorns sea stars,making the consumption of more coral reefs

Posted from my mobile device
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I think there are 2 pairs of answers:

1st as the OA: increase of phy; increase of sea stars

2nd: increase of shrimp, decrease of sea stars.

What is the base to reject the 2nd?
In my opinion the cause-and-effect relation of the shrimp and sea stars are closer (clearly stated that the shrimp decrease THEN stars increase.) than that of the OPTIONAL food choice (phytoplankton, because the stars feed on both phy AND coral polyps) and sea stars.
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parkhydel

Naturalist: The decline of coral reefs has various causes. One contributing factor is predation on coral by organisms such as the crown-of-thorns sea star, whose preferred food source is coral polyps. Human fishing practices have decreased the sea star's predators, such as the harlequin shrimp. It is also possible that runoff containing nutrients for phytoplankton has resulted in larger phytoplankton blooms: the crown-of-thorns sea star gladly eats phytoplankton.

Indicate in the table which cause-and-effect sequence would most likely, according to the naturalist, result in coral reef decline. Make only two selections, one in each column.

CauseEffectStatements
An increase in phytoplankton
A decrease in phytoplankton
An increase in crown-of-thorns sea stars
A decrease in crown-of-thorns sea stars
An increase in harlequin shrimp

Cause: An increase in phytoplankton

Effect: An increase in crown-of-thorns sea stars
Dear Experts, KarishmaB

Why An increase in harlequin shrimp (Cause) does not affect A decrease in crown-of-thorns sea stars (Effect) ?­
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Tanchat

parkhydel

Naturalist: The decline of coral reefs has various causes. One contributing factor is predation on coral by organisms such as the crown-of-thorns sea star, whose preferred food source is coral polyps. Human fishing practices have decreased the sea star's predators, such as the harlequin shrimp. It is also possible that runoff containing nutrients for phytoplankton has resulted in larger phytoplankton blooms: the crown-of-thorns sea star gladly eats phytoplankton.

Indicate in the table which cause-and-effect sequence would most likely, according to the naturalist, result in coral reef decline. Make only two selections, one in each column.

CauseEffectStatements
An increase in phytoplankton
A decrease in phytoplankton
An increase in crown-of-thorns sea stars
A decrease in crown-of-thorns sea stars
An increase in harlequin shrimp

Cause: An increase in phytoplankton

Effect: An increase in crown-of-thorns sea stars
Dear Experts, KarishmaB

Why An increase in harlequin shrimp (Cause) does not affect A decrease in crown-of-thorns sea stars (Effect) ?
An increase in shrimp will cause a decrease in sea stars but will it cause the coral reef to decline? No. We need a cause-effect which will ultimately lead to decline of coral reef. Since sea stars eat coral polyps, a decline in their number will let coral polyps thrive and hence coral reefs should do well.­
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parkhydel
Official Explanation

We are asked to provide a sequence of cause and effect that would (according to the naturalist) result in coral reef decline. The question suggests that the answers will be dependent on one another, in that the correct answer for Cause will depend on the correct answer for Effect, and vice versa.

The passage states that one factor contributing to coral reef decline is predation on coral by organisms such as the crown-of-thorns sea star. The preferred food source for this organism is coral polyps, and so a causal sequence that has as its effect an increase in crown-of-thorns sea stars may be likely to produce a decline in coral reefs. This suggests that the third option may be the correct response for Effect. However, this depends on whether one of the other statements in the table describes a cause suggested by the naturalist to produce this effect.

The last sentence of the naturalist’s statement indeed suggests, in the context of the passage, that an increase in phytoplankton blooms would result in greater numbers of crown-of-thorns sea stars. This suggests that the first option may be the correct response for Effect. And indeed, according to the naturalist, the crown-of-thorns sea star’s preferred food source is coral polyps. All of the naturalist’s statement is about possible explanations of the decline of coral reefs. The passage therefore indicates that the naturalist would take an increase in phytoplankton to produce an increase in crown-of-thorns sea stars, and that this causal sequence would result in coral reef decline.

The correct answer is An increase in phytoplankton.
The correct answer is An increase in crown-of-thorns sea stars.
How did you draw the correlation between phytoplankton(phytop) and crown-of-thorns sea stars(COT)? Since COT gladly eats phytop, apart from coral reefs, if phytop increases, coral reefs should also increase as COT would be more likely to eat COT instead of preying upon coral reefs.­
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­Isn't it the case that decrease in polyplankton --> Sea stars feeding on more coral reefs --> result in coral reef decline?
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Sahana3115
­Isn't it the case that decrease in polyplankton --> Sea stars feeding on more coral reefs --> result in coral reef decline?
­You have to think from the perspective of the Naturalist. He nowhere mentions the sequence of decrease in pp, resulting in sea star feeding on coral reef.

So, we have to stick to what has been mentioned in the argument, as the argument gives the thought process of the naturalist. The Naturalist talks of larger pp blooms, so more food, resulting in more sea stars, who in turn feed on coral polyps, the preferred foof source.
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this question has a faulty understanding. it is notfull proof.
author is two directional in his reasoning and contradicting is line of reasoning
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Can anyone explain this?, Same confusion.
maikikiuu
I think there are 2 pairs of answers:

1st as the OA: increase of phy; increase of sea stars

2nd: increase of shrimp, decrease of sea stars.

What is the base to reject the 2nd?
In my opinion the cause-and-effect relation of the shrimp and sea stars are closer (clearly stated that the shrimp decrease THEN stars increase.) than that of the OPTIONAL food choice (phytoplankton, because the stars feed on both phy AND coral polyps) and sea stars.
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IMO, if 2nd case is true, then that would affect the fact that corals are declining

maikikiuu
I think there are 2 pairs of answers:

1st as the OA: increase of phy; increase of sea stars

2nd: increase of shrimp, decrease of sea stars.

What is the base to reject the 2nd?
In my opinion the cause-and-effect relation of the shrimp and sea stars are closer (clearly stated that the shrimp decrease THEN stars increase.) than that of the OPTIONAL food choice (phytoplankton, because the stars feed on both phy AND coral polyps) and sea stars.
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We are asked to find the cause and effect that would show a decline in coral reef health. As sea stars are a predator of coral, their numbers declining would not cause a decline in coral, rather an increase.
maikikiuu
I think there are 2 pairs of answers:

1st as the OA: increase of phy; increase of sea stars

2nd: increase of shrimp, decrease of sea stars.

What is the base to reject the 2nd?
In my opinion the cause-and-effect relation of the shrimp and sea stars are closer (clearly stated that the shrimp decrease THEN stars increase.) than that of the OPTIONAL food choice (phytoplankton, because the stars feed on both phy AND coral polyps) and sea stars.
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Hello GMATCoachBen, Could you please explain this?
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The explainations fail to explain why an increase of phytoplankton will cause a decrease in coral reef . As CoT star will gladly eats phytoplankton instead of coral reef.
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"preferred food source" is coral reefs.
MohdZaidKhan
The explainations fail to explain why an increase of phytoplankton will cause a decrease in coral reef . As CoT star will gladly eats phytoplankton instead of coral reef.
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MohdZaidKhan
The explainations fail to explain why an increase of phytoplankton will cause a decrease in coral reef . As CoT star will gladly eats phytoplankton instead of coral reef.

I feel this is a slightly weird question. I misunderstood it as well.

The key with TPA's is that the answer choices are super important, so you have to make the answer choices work and fit the question. Here the ideal answer would have been:
Decrease in shrimp predator --> Increase in Sea Stars --> More reef gets eaten up

But this is not one of the options, so we have to look for what makes the most sense after that, which makes this question difficult. You have to recognize that you have pick an imperfect answer combination.

  1. We know that the effect has to be (sort of has to be) the increase in the sea star population, so the effect is fixed.
  2. Now we have to find the cause out of 3 remaining options (since increase/decrease of seastars would not play)
    1. The Shrimp increase has the opposite effect
    2. Decrease in phytoplankton would drive the sea stars to eat the corral reef so it would decrease corral reef but it would probably not increase the sea star population if it decreased
    3. Increase in phytoplankton would on the other hand increase the sea star population but would not potentially increase the reef damange/eating with exception that the sea stars prefer the reefs, so perhaps it would - this is scraping at the bottom of the barrel to get methodically to something.

At this point, you could guess between these 2. I sort of had to as it felt too weak to make the whole question judgement to be based on it.
I am personally not thrilled with the question - not a very black and white one it seems and not very cause-effect so to speak. Just something you would need to print out and diagram out so you remember the marker patterns and the importance of the word preferred.
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