Multicellular animals can have larger body surfaces for gaseous exchange than unicellular organisms. However, these organisms too cannot grow beyond a certain size, since the body surface area does not increase as rapidly as body size or volume. Thus, only a few simple multicellular animal carry out gaseous exchange through their body surface es PR skins without using specialized respiratory structures. Such animals are fairly inactive so that their energy requirements and , as a result, their oxygen demands are low.
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