Examples of animal adaptation to excess moisture.

Animals in freshwater habitats are faced with the problem of continuous osmosis of water into their bodies because their body is hypotonic compared to their external environment. This means that the water will continue to diffuse into the fish until they are at an isotonic concentration between the two environments. Since fish cannot handle such a high concentration of water in their system, evolutionary adaptations have overcome this problem. In the kidneys, which deal with water absorption and are suitable for their function, the glomerulus of the kidney has a large surface area to reduce the concentration of water in the blood. Because these renal tubules allow large-scale movement of ions from the bloodstream, the body needs to reabsorb some important ions, such as salt, back into the bloodstream through active transport.