Well, an interesting question brought up today in class by David!
Sharks have nostrils but they use gills to breathe in oxygen instead. So...
What's the use of having nostrils then?
Check out the answer below !
Nostrils
You use your nose to breath and smell, but the shark only smells through its nostrils. And its olfactory sense is extremely sensitive: It can detect less than one part blood per million parts seawater. Typically, sharks following a scent will weave back and forth through the water like hounds on a fox hunt, holding to the odor's strongest concentration until they find its source.
Gills
Sharks breath by passing seawater over their gills, which harbor tiny filaments that comb oxygen out of the water and shuttle it to the circulatory system. (The gills also get rid of waste products such as carbon dioxide.) Some sharks actively open and close their mouths, pumping water over the gills; others simply leave their mouths open and keep swimming. This is called ram-jet ventilation.
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