* Single celled organisms have a relatively large surface area to volume ratio so all necassary exchanges with the enviroment take place over this surface.
* In multicellular organisims, many organisims are specialised with effective exchange surfaces.
* Exchange surfaces usally have a large surface area and thin walls, which give short diffusion distances. In animals,exchange surfaces will have an efficent blood supply or, for gaseous exchange, be ventitalted.
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