Hot answers tagged underwater
Yes, according to calculations presented here and here the conclusion is that: The O2 diffusion coefficient in saturated air (15% oxygen) is 5,700 to 10,800 times greater than in water (60°C and 20°C respectively). And here is a paper using this difference to investigate the transfer of O2 through the tracheal system of a click beetle.
I'd say that unihemispheric sleep and adaptations like it really are sleep - the brain activity on one side of the brain gives a characteristic sleep pattern. It certainly must satisfy the needs of an aquatic mammal like a dolphin or a whale since they have to be partially conscious to breathe by surfacing regularly. It does seem to affect the brain ...
I suppose that it depends on how sleep is defined. If we define it a a mechanism by which the brain repairs itself in an altered state, then, yes they do indeed sleep. Just not with all of their brain at once.
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