PT146.S2.Q1

PrepTest 146 - Section 2 - Question 1

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For the first few weeks after birth, the dunnart has such poor control over its respiratory muscles that it cannot use them to breathe. Instead, this tiny marsupial breathes through its thin skin, which gradually thickens as the dunnart matures inside its mother's pouch. The dunnart is unique among warm-blooded animals, the rest of which need thick skin throughout their lives to maintain body temperature and reduce water loss.

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1.

Which one of the following, if true, most helps explain how newborn dunnarts manage to survive despite their thin skins?

a

The dunnart's respiratory muscles begin to develop a few days after birth.

We know that baby dunnarts breathe through their thin skin because they cannot yet control their respiratory muscles. But (A) does not explain how they maintain their body temperature and reduce water loss before those respiratory muscles develop.

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b

The dunnart's body temperature is higher than that of many other warm-blooded animals.

Having a higher body temperature does not explain how baby dunnarts maintain that body temperature and reduce water loss with thin skin.

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c

Adult dunnarts experience more heat and water loss through their skin than other adult marsupials do.

Dunnarts’ skin gradually thickens as they mature. So we know that adult dunnarts can maintain their body temperature and reduce water loss, even if they don’t do so as efficiently as other adult marsupials. We need an explanation for how baby dunnarts can do this with thin skin.

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d

Its mother's pouch keeps a newborn dunnart warm and reduces water loss through its skin.

This explains the key difference in how young dunnarts maintain body temperature and reduce water loss. While other warm-blooded baby animals need thick skin to survive, its mother’s pouch keeps a baby dunnart warm and reduces water loss, so the baby can survive with thin skin.

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e

Some dunnarts live where daytime temperatures are high and the climate is dry.

This does not help to explain how baby dunnarts can survive with thin skin. Even if they are in a warmer and drier climate, we still need to know how they are able to maintain their body temperature and reduce water loss.

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