A blowhole is the hole at the top of the whales head through which the animal breathes air.
In baleen whales, those whales who do not have teeth, but rather have baleen plates to filter food out of the water , blowholes are in pairs – positioned in a V-shape . It is homologous with the nostril of other mammals, and evolved via gradual movement of the nostrils to the top of the head.
Toothed whales have only one blowhole. The blowhole of a sperm whale, a toothed whale, is located left of center in the frontal area of the snout, and is actually its left nostril, while the right nostril lacks an opening to the surface and its nasal passage is otherwise well developed.
The trachea only connects to the blowhole, and the animal cannot breathe through its mouth. Because of this, there is no risk of food accidentally ending up in the animal’s lungs, so whales have no gag reflex.
Part of their ability to stay underwater so long comes down to the size of their lungs which are, as you can imagine, pretty large (to give you an idea, a blue whale’s lung capacity is 5000 liters, or 1320 gallons). However, it also has to do with the way whales are able to process the air that goes in. It’s estimated that whales use about 90% of the oxygen that enters their lungs, making the most of each breath. In comparison, humans are estimated to use only about 15% of the oxygen we breathe.