Without oxygen. mammals could not breathe, move or turn foThe primary purpose of the respiratory system is to bring oxygen to the lungs and remove any unnecessary gases. Without oxygen. mammals could not breathe, move or tum food into energy. All animals need oxygen to live. This is true whether it is humans who breathe through their mouths, fish who breathe through their gills or reptiles who breathe through their skin. In each case, there is an exchange of gases in the body. The respiratory system in mammals has a passageway that goes from the mouth to the lungs for breathing. It is most commonly called the windpipe.od into energy. All animals need oxygen to live. This is true whether it is humans who breathe through their mouths, fish who breathe through their gills or reptiles who breathe through their skin. In each case, there is an exchange of gases in the body. The respiratory system in mammals has a passageway that goes from the mouth to the lungs for breathing. It is most commonly called the windpipe.