Both aquatic and terrestrial organisms must have across which gas exchange can take place.

Both aquatic and terrestrial organisms must have a respiratory system across which gas exchange can take place

A respiratory system is a biological system which consists of definite organs and structures used for gas exchange in animals and plants. In most aquatic organisms such as fish, the respiratory system consist of gills in which gas exchange takes place. The gills is immersed in a watery environment and water flows over it by a variety of active or passive means. In terrestrial organisms, gas exchange takes place in the lungs.

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