​

Amphibians

 

Amphibians use three types of respiration throughout their lifespan. When they are tadpoles at the beginning of their lives, they breathe much like fish - using gills. Once they grow up and transform into land animals, they can breathe either through their skin or using their lungs.

While many other chordates use negative pressure for respiration, amphibians instead use positive pressure to breathe. When using their lungs, they actively move their throats to push air into their lungs. There, in small sacs called the alveoli, oxygen diffuses into the bloodstream and carbon dioxide diffuses out of it. When breathing through their skin, oxygen diffuses directly through their skin into their blood and carbon dioxide diffuses out (Chordata Respiratory System).

​

Reptiles, Birds and Mammals

 

Animals like reptiles, birds, and mammals use negative pressure breathing. This type of breathing occurs when certain muscles in an organism expand the lungs. Humans, reptiles, and birds all take in oxygen through their nose and mouth. Air goes from the pharynx, located behind the tongue, into the trachea, or windpipe. For mammals and reptiles, the trachea branches into right and left bronchi, which continue to branch into alveoli, the place where gas exchange occurs (Chordate Circulatory).

 

Reptiles use the muscles that are attached directly to the rib cage to expand their lungs, limiting sizable movement during breathing. Mammals however, use a muscle called the diaphragm. The lungs start to expand as the diaphragm contracts, creating the negative pressure necessary for breathing to occur. The diaphragm is not connected to any other skeletal muscle, allowing for long periods of movement.

​

​

​

​

The phylum Chordata has the most evolved respiratory systems out of all of the phyla that have been researched on this particular site. They have multiple organs and have distinct but intertwined systems, which allows organisms in the Chordata phylum to maximize their ability to respire effectively, which can effectively reduce the amount of energy and time required to maintain homeostasis. Thus by having a more evolved respiratory system, organisms can free up energy and time, which allows the organism to focus on other tasks and become ultimately more complex when compared to previous phyla.