PrepTest 113, Section 2, Question 20
Antarctic seals dive to great depths and stay(39 more words not shown)
Each of the following, if(9 more words not shown)
- AHorses are known(11 more words not shown)
- BMany species of(9 more words not shown)
- CThe oxygen contained(17 more words not shown)
- DThe spleen is(16 more words not shown)
- EThe spleens of(17 more words not shown)
Reading the argument
How do these seals have enough oxygen to stay underwater for hours? The passage gives us part of an answer: they use oxygen in their blood as well as their lungs. Then the researchers propose an additional store of oxygenated blood in the spleen. Why the spleen? I'd want evidence connecting that organ to the long dives.
What we’re looking for
Four choices strengthen that proposal, and we need the exception. They don't each have to prove the hypothesis. A fact that makes it more plausible can help; the odd one out won't supply that support.
Working the answers
- A
Horses provide an example of another animal using its spleen to store oxygenated blood for exertion. Horses and seals are different, so this doesn't prove the seal hypothesis. Still, it shows that the proposed use of a spleen occurs in another animal. That makes the suggestion more plausible than if we had no reason to think a spleen could serve that function. A offers limited support, which is enough to keep it from being the exception.
- BCorrect
Oxygen stored directly in muscle tissue doesn't support oxygenated blood being stored in a spleen. It's a different location and a different proposed store. We also aren't told that the many species mentioned include the Antarctic seals in question.
Even if those seals could use muscle storage, that would explain another possible supply of oxygen, not establish the particular spleen hypothesis. B might point toward an alternative contribution to their diving ability. It gives us no added reason to think the spleen stores oxygenated blood, so this is the exception.
- C
If the lungs and bloodstream alone don't provide enough oxygen, some additional supply is needed to account for the dives. That gives a reason to investigate the proposed extra store. C doesn't identify the spleen on its own, but it supports the need that the spleen hypothesis is meant to fill. Strengthening can be partial.
- D
A larger spleen in these long-diving seals, compared with aquatic mammals that don't make long dives, connects the organ with the ability we're explaining. Perhaps the larger organ provides more storage. That's a possible explanation of the size difference, not something D proves, but the association gives the researchers' hypothesis some support.
- E
A high concentration of blood vessels gives a reason to think the spleen is well suited to a role involving blood. It doesn't establish that the blood is stored there, or that its oxygen actually supports a dive. But it adds a relevant feature of the proposed organ, making the blood-storage idea more plausible. That's support for the hypothesis, unlike B's fact about muscle tissue.
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