Properties of Water

Water is so important because of its molecular structure. Without its unique characteristics, water would not be able to serve the functions it does. The molecular formula of water is H2O. A central oxygen atoms shares two of the electrons floating in its outer layer with one electron each from two hydrogen atoms.

Buoyancy

Buoyancy is the upward force that water exerts. It is what keeps ice cubes, which are less dense than liquid water, floating in a glass. Density is the mass of an object per unit of volume, and buoyancy is the ability of water to let objects (or liquids) that are less dense float in it. This is important because it provides physical support in aquatic environments. The fish and other organisms have developed structures based on the fact that water reduces the pull of gravity. This also minimizes the need for large supporting structures in order to move around. Organisms move through water differently than they move on land, and their outer appearances reflect this. Buoyancy also plays a role in helping animals move vertically. Because these creatures are surrounded by water, they can move in any direction in three dimensions, including vertically. On land, this can only be accomplished with wings or especially strong legs (for short periods of time). Fish only need to develop fins (no need for wings) to take advantage of increased mobility.

Heat capacity

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Heat capacity is the capability of water to absorb heat without undergoing an increase in temperature. Water has a high heat capacity of ---. This means that even though heat energy is entering a body of water, that energy will not be reflected in the measured temperature of the water until more heat has been added. High heat capacity plays a vital role in regulating global climate. A good example of this is that coastal regions typically have cooler climates than regions that are further in land. This is because the ocean water absorbs heat from the land, which has a lower heat capacity, and the temperatures increase at a slower rate. This effect of water is extended across the globe because 78%--? of Earth is made up of water. In addition to a widespread effect on the planet, water’s heat capacity helps animals regulate their internal temperatures, which must be sustained within a certain range. For aquatic organisms, the external environment is subject to fewer extreme temperature changes, so internal heat is easier to maintain constant.

Surface tension

Surface tension helps water molecules hold together. This allows the formation of rain, which dissolves nutrients in soil.

Filtration

Water filters ultraviolet rays that penetrate the Earth's atmosphere in the form of sunlight.

Polarity

A polar molecule is one in which the electric charge is not evenly distributed between the atoms. The oxygen atom in a molecule of water attracts electrons with a negative charge more strongly than the two hydrogen atoms. This means that one end of the molecule has a slightly negative charge while the other end has a slightly positive charge. Therefore, water is a good solvent, meaning that many substances can dissolve in water since nonpolar substances tend to dissolve in nonpolar solvents. Because of this, aquatic plants can obtain nutrients directly from the water (unlike terrestrial plants, which must obtain them from a combination of air and soil). Water can also transport molecules throughout organisms and throughout the Earth, and it dilutes and dissolves pollutants.

Thinkquest Team "Fish," March 2005, Disclaimer and copyright information
Image source: Scott Van Bramer