1. Water Intake: Sharks open their mouths and take in water while swimming. Water enters the shark's mouth and passes through the pharynx (throat).
2. Filtration: The pharynx contains gill slits, which are covered by gill filaments. The gill filaments are thin, feathery structures that filter out suspended particles, such as plankton and small organisms, from the water. The filtered water continues to pass over the gills.
3. Oxygen Exchange: The gill filaments are lined with tiny blood vessels called capillaries. As water flows over the gill filaments, oxygen from the water diffuses across the capillaries and enters the bloodstream. At the same time, carbon dioxide, a waste product of cellular respiration, diffuses out of the bloodstream and into the water.
4. Water Expulsion: After the exchange of oxygen and carbon dioxide, the water is expelled through the gill slits. The shark expels the water forcefully by contracting muscles around the gill chamber.
5. Continuous Breathing: Sharks must continuously move water over their gills to obtain oxygen and expel carbon dioxide. Therefore, they are obligate ram ventilators, meaning they must keep swimming to breathe. Even while resting, sharks maintain a low level of swimming activity to ensure a constant flow of water over their gills.
It's important to note that sharks have multiple pairs of gill slits, typically five to seven on each side of their head. This arrangement of gills allows for a large surface area for efficient gas exchange. Additionally, some shark species have specialized adaptations, such as spiracles (small openings on the top of the head), which help them breathe while resting on the sea floor.
The efficient鳃of sharks enable them to extract oxygen from water and respire effectively in their aquatic environment.