System is to bring oxyten to the lungs and remove anny ynnecsessary gases. Without oxygen, mammals could not breathe, move or turn food into ienergy. All animal 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 mamamals has a passageway that goes from the mouth to the lungs for breathing. It is most commonly called the windpipe