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Which of the following does the author suggest about endotherms' responses to heat and cold?
This answer choice incorrectly presumes that excess cold cannot have a drastic and detrimental effect on endotherms. However, although endotherms have more trouble coping with excess heat than excess cold, there is no information in the passage to suggest that detrimental effects on endotherms are necessarily caused only by excess heat.
The second sentence of the first paragraph tells us that an endotherm raises its metabolic rate to produce heat. However, we have no information to suggest that it does the obverse to dissipate heat.It is possible that the endotherm may maintain the same metabolic rate, and dissipate its excess heat by other means; the passage does imply otherwise.
Since endotherms produce some heat as they dissipate it, the process of dissipating heat is less effective than its counterpart. Thus, an endotherm will be better able to react to a temperature which requires heating than to a temperature which requires heat dissipation (since the animal would be heated more efficiently than it would be cooled).
Although it is true that an endotherm responds to excess heat less efficiently than it responds to excess cold, the relative amount of heat and cold matter. It would not be correct to make a blanket statement, as this answer choice does, that any amount of excess heat (even a small amount) has a greater effect on an endotherm than any amount of excess cold.
The fact that the dissipation of heat is not as efficient a process as its production only means that an endotherm must spend more energy dissipating heat than it would producing it. Moreover, if endotherms really could not dissipate heat, the author would not say in the first sentence of the passage that endotherms' internal temperatures do not vary by more than a few degrees centigrade over the animals' lifetimes.