It most CERTAINLY IS NOT cellular respiration!! I would probably go with passive diffusion. Cell respiration is when eurkaruotuc organisms convert oxygen into carbon dioxide essentially
I'm presuming you mean the three different subcatagories or taxa as there around 25/26 mammalian orders. The three taxa are - Prototheria or Monotreme = Mammals that lay eggs Metatheria Marsupial = Mammals with external development pouches.
