Compare and contrast the ways different animals respond to osmotic challenges

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Compare and contrast the ways different animals respond to osmotic challenges

Water is essential for all forms of life. By having a high specific heat capacity of 4.2 J g-1 K-1, it is able to retain heat efficiently and resist small fluctuations of temperature. It is also a very effective solvent, acting as a transport medium for various substances such as oxygen, amino acids, polysaccharides and other polar molecules. It is therefore important that water levels in organisms can be maintained and controlled. The regulation of water and solutes, and therefore osmotic pressure, is known as osmoregulation.

Osmoregulation is important for cell integrity: if the osmotic pressure inside the cell is too high, the cell swells and eventually bursts due to continued osmotic movement of water into the cell; if the osmotic pressure inside the cell is too low, the cell shrinks. The composition of the extracellular fluid surrounding the cells is different in different animals, thus the cells in different are in different environments. This reflects different animals living in different environments themselves, for example, land animals living in dry or humid conditions and fish living in fresh water or seawater. Thus, animals living in different environments will experience different osmoregulatory challenges and therefore employ different osmoregulatory organs to help maintain their internal environments. This essay will consider the osmoregulatory organs in turn and how they function to allow organisms to survive in their environment.

The most basic osmoregulatory organ in some animals is the integument separating the organisms’ internal environment from the external environment. Amphibians such as frogs have a moist and cool kin, which acts as a free water surface (Schmidt-Nielsen, 1997) where water intake takes place since amphibians do not drink (Withers, 1992). The evaporation rate is high, so amphibians generally live near water and humid environments. Because the body fluids in amphibians living in freshwater are more concentrated than the surrounding water, amphibians gain water and lose salts across the skin. The loss of salts is overcome by channel pumps such as H+ V-ATPase and Na+/K+ P-ATPase, which actively transport ions in to the skin. Aquatic insects, which also have body fluids hyperosmotic to their environment, employ a similar mechanism and so water enters through their body surface. Some frogs and insects also have a waxy layer on their skin to limit water loss. Thus, water can be gained when these animals are in a freshwater environment due to osmotic inflow and water can be lost in terrestrial environments due to evaporation.

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The respiratory organs act as an interface for water exchange and in some cases salt exchange as well. In mammals, an obligatory exchange occurs in the lungs – water is lost from the lungs by evaporation. In fish, the direction of water and ion movement ids dependent on the environment (marine or freshwater) though osmoregulation is achieved through the use of chloride cells. In marine teleosts, water is lost across the gills and Na+ and Cl- are gained across the gills as the body fluids are more dilute than the seawater. The chloride cells secrete Cl- against its gradient through the use ...

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