Water is essential for life. This is why astronomers search for the presence of water on distant planets, even in the form of ice. There is a potential for life on Jupiter's moon, Europa, because water is found not only in its solid form, but as a liquid as well. Ice coats the moon's surface and liquid water is suspected to be beneath the ice. This is an important phenomenon because water serves many purposes to organisms.
Chemical Reactions
Water is necessary for the chemical reactions that occur within the body because those reactions must take place in a liquid environment. Cellular metabolism is a collection of important reactions in which molecules are either broken down or created for use by the body or for excretion.
Structural Support
Many animals have skeletons that maintain their shape. Plants, however, do not contain a skeleton that supports their structure. Turgidity, or turgor pressure, occurs when a plant's cells are filled with water. This increases the pressure of one cell against another and stiffens the plant structure allowing it to stand upright. This occurs because water is not compressible and maintains the same volume. Inadequate water volume results in little pressure among the cells and the plant wilts.
Cooling the Body through Sweating
Sweat is largely made up of water. Many animals sweat when their body temperatures become too high. The sweat is excreted to the surface of the skin where it draws heat from the body. When the sweat becomes warm enough, it evaporates and carries the heat away.
Lubrication
Lubrication is necessary for many of the body's processes. Saliva is largely composed of water and is a lubricant that allows food to be swallowed. Fluids are found within membrane layers to allow the body's organs to freely slide with movement. Many joints, including the knee, contain serous fluid that allows the joint cartilage to freely move.
Cohesion and Adhesion
Cohesion is the attraction of water molecules to other molecules. It is the result of hydrogen bonding – the attraction of the hydrogen atoms in water to the oxygen atoms in water. It is the property that allows water droplets to form. Cohesion is responsible for surface tension. This property allows some insects to walk across water.
Adhesion is the ability of water to stick to other surfaces. For example, water forms on mirrors in a steamy bathroom. Adhesion is a property that causes water to be drawn up through soil and into paper towel. When water is drawn up through small spaces, it is called capillary action.
Water is an amazing substance that is critical to life. It serves a purpose in various processes such as cellular metabolism, heat transfer, and structural support. For these reasons and more, the presence of water is a good indicator that life may be sustainable in certain environments, such as the Jovian moon of Europa.
Reference
Brooker, Robert J., Widmaier, Eric P., Graham, Linda E., and Stiling, Peter D. Biology. New York: McGraw-Hill, 2008.
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