breathing is a process in animal respiration & animals require respiration to survive / use energy ->  animals must breath to survive  animals must breath to survive & breathing is when animals convert oxygen into carbon dioxide ->  an animal requires oxygen for survival / to breathe  an animal requires oxygen for survival / to breathe & if something is required by something else then that something must be provided to that somethign else ->  oxygen must be provided to animals in order for them to breathe / survive  some environments contain waste & waste must be removed ->  waste must be removed from environments that contain waste  breathing out is when animals expel carbon dioxide from their lungs into the air & if something is expelled in a process, then that something is a waste product of that process ->  carbon dioxide is a waste product of the breathing process  carbon dioxide is a waste product of the breathing process & breathing is a process in animal respiration ->  in the animal respiration process carbon dioxide is a waste product  waste must be removed from environments that contain waste & in the animal respiration process carbon dioxide is a waste product ->  carbon dioxide must be removed from an environment where animals are performing respiration  oxygen must be provided to animals in order for them to breathe / survive & carbon dioxide must be removed from an environment where animals are performing respiration -> in an environment where animals are breathing / performing respiration, oxygen must be provided and carbon dioxide must be removed