The organisms living on the land use oxygen directly from the atmosphere. The different organs absorb this oxygen. These organs have a structure that increases surface area to absorb this oxygen. Marine animals have to use dissolved oxygen. The amount of oxygen in water is fairly low as compared to the atmosphere. Because of this, the breathing rate of aquatic animals increases. The fishes take oxygen from the mouth, and then the oxygen passes through the gills, which are taken up by the blood.