Dolphins are able to sleep without drowning because they have gills, like fish do. have a special opening that allows air in but not water. sleep on just one side of their brain at a time. inflate their bodies before sleep, which maintains them floating upright so they can breathe without taking in any water.

They sleep on just one side of their brain at a time

Explanation:

Dolphins are different from fishes that can breathe underwater.

It is necessary for them to get to the surface of the water at intervals to breathe air.

While sleeping, dolphins allows one hemisphere of their brains fall asleep while the other half is fully conscious. This means that If the left brain is sleeping, the right eye stays open and if the right brain is sleeping, the left eye stays open.

This happens so they always know when it's time to surface and breathe and when to escape when there is trouble.

sleep on just one side of their brain at a time

Explanation: While sleeping, the dolphin shuts down only half of its brain together with the opposite eye while the other half of the brain stays awake at a minimum level of alertness. It uses its attentive side to watch for predators or obstacles. The dolphin also reverses this process to rest the active side of the brain and awake the rested half.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!