Sharks have a unique respiratory system that allows them to breathe underwater. They have five to seven gill slits on either side of their head, and each of these slits is lined with filaments that are covered in tiny blood vessels. As water passes over the gills, the oxygen in the water is absorbed by the blood vessels and transported throughout the shark's body.
Dolphins
Dolphins are mammals, and as such, they have lungs that they use to breathe air. However, dolphins can also hold their breath for long periods of time, thanks to a number of adaptations that allow them to conserve oxygen. These adaptations include:
* A large lung capacity: Dolphins have lungs that are about twice the size of human lungs, which allows them to store a large amount of oxygen.
* A slow metabolic rate: Dolphins have a slow metabolic rate, which means that they do not use oxygen as quickly as other animals.
* The ability to hold their breath for long periods of time: Dolphins can hold their breath for up to 20 minutes, and some species can even hold their breath for up to 30 minutes.
When a dolphin surfaces to breathe, it will take a quick breath of air and then immediately dive back underwater. The dolphin's lungs are located at the top of its body, so when it surfaces, it can take a breath without having to raise its head out of the water.