It is understood from the passage that.......

All plants and animals depend on oxygen to grow and live. This gas is taken in during the process known as breathing or external respiration. Simple organisms are able to absorb oxygen through the surface of their bodies, but most larger animals require a special area, which in mammals, for example, is situated in the lungs. Fish are equipped with gills, where oxygen is extracted from the water taken in and passed into the bloodstream. Some other animals which live in or near water, such as frogs, have moist skin through which the gas is able to permeate. Whichever way it is absorbed, the use made of oxygen taken in is known as internal or chemical respiration.