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 Post subject: GMAT Verbal
PostPosted: Wed Aug 22, 2012 8:50 am 
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The environment of the lower ocean depths differs markedly from other aquatic environments. Chief among these differences are elevated pressure and lack of light. These conditions cause difficulties in the locating of food, avoidance of predators and even finding a mate for the denizens of the ocean depths, sometimes referred to as deep sea creatures. Pressure increases by roughly one atmosphere for every ten meters of depth and may be as high as 1,000 atmospheres at the ocean floor. The near-total lack of sunlight renders photosynthesis impossible and has given rise to the term "sub-photic zone" as synonymous with the lower ocean depths. These factors place certain restrictions upon the characteristics of lower-ocean-dwelling organisms and have forced a variety of adaptations onto them, allowing them to cope better with their harsh and unusual environment.

Several generalized adaptations to the elevated pressure are seen. Most deep sea organisms are rather small, rarely exceeding 25 cm in length. Additionally, the deeper a creature lives, the more gelatinous its flesh and the more minimal its skeletal structure. Deep sea dwellers have also totally eliminated or minimized the size of excess cavities that would collapse under the pressure, such as swim bladders.

One adaptation to the near total lack of light can be seen in eye morphology. Most deep sea species have very large eyes with retinas constructed only of cones, which increases the amount of light entering the eyes. Another adaptation is seen in the large number of bioluminescent organisms present in the ocean depths. Bioluminescence is a process whereby organisms generate light through the reaction of the compound luciferin with the enzyme luciferase. An extreme reliance on bioluminescence can be found in the vampire squid. The highly sensitive eyes of deep sea predators are able to distinguish the silhouettes of their prey as they swim above or beneath them. To combat this, the vampire squid generates its own bluish light, masking its silhouette in a strategy called counterillumination. The vampire squid is also covered with bioluminescent light-producing organs called photophores, which are capable of producing disorienting flashes of light for as long as several minutes, allowing the vampire squid time to escape from closer encounters with its predators.


All of the following are characteristics of deep sea creatures that reflect adaptations to the sub-photic zone EXCEPT
A. large eyes
B. limited skeletal structure
C. decreased photosynthesis
D. small size
E. photophores



(C) The second and third paragraphs list many adaptations, so there's a lot of material to work with. (B) and (D) are discussed in the second paragraph as adaptations to elevated pressure, so neither of those is correct. Large eyes are mentioned early in the third paragraph, and photophores are the organs that allow vampire squid to produce light. That leaves us only with choice (C), which is a characteristic of the environment, not of the creatures themselves.
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I would argue E is the answer.

Photosynthesis is mentioned in the text at the top and it states that is rendered impossible in deep waters. So creatures can't perform it there (e.g. corals that are actually creatures and not plants. Not mentioned in the text but it does not actually need to be mentioned. Just proving it's plausible).

The text just states the vampire squid has photophores. It does not state that photophores are exclusively found in deep waters. So maybe different creature may have photophores in shallow water, we don't know.

So E seems more safe of answer to me.


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 Post subject: Re: GMAT Verbal
PostPosted: Wed Aug 22, 2012 8:53 am 
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Joined: Thu Jul 05, 2012 11:55 am
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questioner wrote:
I would argue E is the answer.

Photosynthesis is mentioned in the text at the top and it states that is rendered impossible in deep waters. So creatures can't perform it there (e.g. corals that are actually creatures and not plants. Not mentioned in the text but it does not actually need to be mentioned. Just proving it's plausible).

The text just states the vampire squid has photophores. It does not state that photophores are exclusively found in deep waters. So maybe different creature may have photophores in shallow water, we don't know.

So E seems more safe of answer to me.
Photophores are mentioned in relation to the increased use of bioluminescence that is one adaption of deep sea creatures. Photophores need not be found exclusively in deep waters for them to be one adaption of deep sea creatures. Decreased photosynthesis (choice C), is the only option that is a characteristic of the environment, not of the creatures, and therefore it is the only correct choice.


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