Bottlenose dolphins breathe air but can sleep in the ocean because ________.
A) they sleep for only 30 minutes at a time, which is the maximum interval they can cease breathing
B) they fill their swim bladder with air to keep their blowholes above the surface of the water while they sleep
C) they move to shallow water to sleep, so they do not need to swim to keep their blowholes above the surface of the water
D) they alternate which half of their brain is asleep and which half is awake

Question

Quizplus · Accepted Answer

Bottlenose dolphins have the ability to rest one half of their brain at a time while the other half remains awake to control breathing, keep the dolphin swimming slowly to the surface for air, and watch for predators. This is called unihemispheric sleep, which allows them to sleep in the ocean without suffocating. Therefore, choice (D) is the correct answer. Choice (A) is not entirely true because dolphins can actually sleep for up to two hours at a time, but they still use unihemispheric sleep. Choice (B) and (C) are also not correct since bottlenose dolphins do not have a swim bladder and they do not always move to shallow water to sleep.

Bottlenose Dolphins Breathe Air but Can Sleep in the Ocean