sentences: the respiratory system takes in oxygen from the air & the respiratory system is a part of the body ->  the respiratory system takes oxygen from the air into the body  the respiratory system takes oxygen from the air into the body & air is a part of the environment ->  the respiratory system takes oxygen from the environment into the body  the lungs are a part of the respiratory system & the lungs are a part of the body of an animal used for breathing air ->  the respiratory system is used for breathing  the respiratory system is used for breathing & breathing is when animals convert oxygen into carbon dioxide ->  the respiratory system is used for converting oxygen into carbon dioxide by breathing  the respiratory system takes oxygen from the environment into the body & the respiratory system is used for converting oxygen into carbon dioxide by breathing ->  the respiratory system takes oxygen from the environment into the body and converts it to carbon dioxide by breathing  breathing out is when animals exhale / expel carbon dioxide from their lungs into the air & air is a part of the environment ->  breathing out is when animals expel carbon dioxide from their lungs into the environment  breathing out is when animals expel carbon dioxide from their lungs into the environment & lungs are a part of the body ->  breathing out is when animals expel carbon dioxide from their body into the environment  the respiratory system takes oxygen from the environment into the body and converts it to carbon dioxide by breathing & breathing out is when animals expel carbon dioxide from their body into the environment ->  the respiratory system takes oxygen from the environment into the body and expels carbon dioxide from the body into the environment by breathing  the respiratory system takes oxygen from the environment into the body and expels carbon dioxide from the body into the environment by breathing & to exchange things between something and something else means that something takes in one kind of thing from that something else and expels another kind of thing into that something else -> the respiratory system is used for exchanging oxygen and carbon dioxide between the body and the environment