<Tr> <Td> Cnidarians </Td> <Td> Oral arms </Td> <Td> Usually one cell </Td> <Td> Water movement </Td> <Td> None </Td> </Tr> <Tr> <Td> Reptiles </Td> <Td> Many lamellae and filaments per gill </Td> <Td> Alveolus and capillary (two cells) </Td> <Td> Countercurrent flow </Td> <Td> Lungs </Td> </Tr> <Tr> <Td> Amphibians </Td> <Td> Many lamellae and filaments per gill </Td> <Td> Alveolus and capillary (two cells) or one cell </Td> <Td> Countercurrent flow </Td> <Td> Lungs, skin and gills </Td> </Tr> <Tr> <Td> Plants </Td> <Td> High density of stomata; air spaces within leaf </Td> <Td> One cell </Td> <Td> Constant air flow </Td> <Td> Stomata </Td> </Tr>

The diagram shows how gas exchange happens in a specialised structure of the lungs