Question

the oceanic whitetip shark and the pacific halibut are ectothermic (cold - blooded) fish, whereas the shortfin mako shark and the yellowfin tuna are regional endotherms—they retain metabolic heat resulting in body temperatures above the ambient water temperature. modeling the effect of falling ambient temperatures on ectotherms indicated to researchers haley r. dolton and colleagues that ectotherms body temperatures inexorably decrease toward the ambient temperature. data from wild basking sharks show that even though their body temperature consistently remains 1.0 to 1.5°c above ambient, it also declines as the ambient temperature falls. this suggests that the body temperatures of the
which choice most logically completes the text?
a) yellowfin tuna and the shortfin mako shark are likely to be more variable than the body temperature of the basking shark.
b) pacific halibut and the basking shark are at least partly determined by the ambient water temperature.
c) basking shark and the shortfin mako shark remain fixed even as ambient water temperature changes, while the body temperature of the pacific halibut changes with variations in the ambient water temperature.
d) basking shark and the yellowfin tuna remain fixed even if the ambient water temperature changes, while the body temperature of the oceanic whitetip shark varies even if the ambient temperature is stable.

Explanation:

• The text states that ectothermic (cold - blooded) fish like the oceanic whitetip shark and Pacific halibut have body temperatures that are affected by ambient temperature. Modeling shows ectotherms' body temperatures decrease toward ambient. Data from basking sharks (which are likely ectotherms as their body temp is related to ambient) shows body temp declines as ambient falls.
• Option B: Pacific halibut (ectotherm) and basking shark (implied ectotherm) have body temps at least partly determined by ambient. This aligns with the text's discussion of ectotherms and their relation to ambient temperature.
• Option A: Yellowfin tuna and shortfin mako shark are regional endotherms. The text focuses on the relationship of ectotherms (like the ones in option B) to ambient, not comparing endotherms to basking shark.
• Option C: Shortfin mako shark is a regional endotherm. The text does not say their body temp remains fixed. Also, it contradicts the idea that basking shark (implied ectotherm) would have a fixed temp as the text shows its temp is related to ambient.
• Option D: Yellowfin tuna is a regional endotherm. The text does not support the claim that their temp remains fixed. Also, it misrepresents the relationship of oceanic whitetip shark (ectotherm) whose temp should be related to ambient, not vary when ambient is stable.

Answer:

B. Pacific halibut and the basking shark are at least partly determined by the ambient water temperature.